Commit f47824f24d

Andrew Kelley <andrew@ziglang.org>
2024-05-23 20:25:41
std: restructure child process namespace
1 parent 793f820
lib/compiler/aro/aro/Driver.zig
@@ -803,7 +803,7 @@ pub fn invokeLinker(d: *Driver, tc: *Toolchain, comptime fast_exit: bool) !void
             return d.fatal("unable to dump linker args: {s}", .{errorDescription(er)});
         };
     }
-    var child = std.ChildProcess.init(argv.items, d.comp.gpa);
+    var child = std.process.Child.init(argv.items, d.comp.gpa);
     // TODO handle better
     child.stdin_behavior = .Inherit;
     child.stdout_behavior = .Inherit;
lib/compiler/std-docs.zig
@@ -302,7 +302,7 @@ fn buildWasmBinary(
         "--listen=-",
     });
 
-    var child = std.ChildProcess.init(argv.items, gpa);
+    var child = std.process.Child.init(argv.items, gpa);
     child.stdin_behavior = .Pipe;
     child.stdout_behavior = .Pipe;
     child.stderr_behavior = .Pipe;
@@ -437,7 +437,7 @@ fn openBrowserTabThread(gpa: Allocator, url: []const u8) !void {
         .macos => "open",
         else => "xdg-open",
     };
-    var child = std.ChildProcess.init(&.{ main_exe, url }, gpa);
+    var child = std.process.Child.init(&.{ main_exe, url }, gpa);
     child.stdin_behavior = .Ignore;
     child.stdout_behavior = .Ignore;
     child.stderr_behavior = .Ignore;
lib/std/Build/Step.zig
@@ -275,7 +275,7 @@ pub fn evalChildProcess(s: *Step, argv: []const []const u8) !void {
     try handleChildProcUnsupported(s, null, argv);
     try handleVerbose(s.owner, null, argv);
 
-    const result = std.ChildProcess.run(.{
+    const result = std.process.Child.run(.{
         .allocator = arena,
         .argv = argv,
     }) catch |err| return s.fail("unable to spawn {s}: {s}", .{ argv[0], @errorName(err) });
@@ -313,7 +313,7 @@ pub fn evalZigProcess(
     try handleChildProcUnsupported(s, null, argv);
     try handleVerbose(s.owner, null, argv);
 
-    var child = std.ChildProcess.init(argv, arena);
+    var child = std.process.Child.init(argv, arena);
     child.env_map = &b.graph.env_map;
     child.stdin_behavior = .Pipe;
     child.stdout_behavior = .Pipe;
@@ -480,7 +480,7 @@ pub inline fn handleChildProcUnsupported(
 
 pub fn handleChildProcessTerm(
     s: *Step,
-    term: std.ChildProcess.Term,
+    term: std.process.Child.Term,
     opt_cwd: ?[]const u8,
     argv: []const []const u8,
 ) error{ MakeFailed, OutOfMemory }!void {
lib/std/process/Child.zig
@@ -0,0 +1,1795 @@
+const std = @import("../std.zig");
+const builtin = @import("builtin");
+const unicode = std.unicode;
+const fs = std.fs;
+const process = std.process;
+const File = std.fs.File;
+const windows = std.os.windows;
+const linux = std.os.linux;
+const posix = std.posix;
+const mem = std.mem;
+const EnvMap = std.process.EnvMap;
+const maxInt = std.math.maxInt;
+const assert = std.debug.assert;
+const native_os = builtin.os.tag;
+const ChildProcess = @This();
+
+pub const Id = switch (native_os) {
+    .windows => windows.HANDLE,
+    .wasi => void,
+    else => posix.pid_t,
+};
+
+/// Available after calling `spawn()`. This becomes `undefined` after calling `wait()`.
+/// On Windows this is the hProcess.
+/// On POSIX this is the pid.
+id: Id,
+thread_handle: if (native_os == .windows) windows.HANDLE else void,
+
+allocator: mem.Allocator,
+
+/// The writing end of the child process's standard input pipe.
+/// Usage requires `stdin_behavior == StdIo.Pipe`.
+/// Available after calling `spawn()`.
+stdin: ?File,
+
+/// The reading end of the child process's standard output pipe.
+/// Usage requires `stdout_behavior == StdIo.Pipe`.
+/// Available after calling `spawn()`.
+stdout: ?File,
+
+/// The reading end of the child process's standard error pipe.
+/// Usage requires `stderr_behavior == StdIo.Pipe`.
+/// Available after calling `spawn()`.
+stderr: ?File,
+
+/// Terminated state of the child process.
+/// Available after calling `wait()`.
+term: ?(SpawnError!Term),
+
+argv: []const []const u8,
+
+/// Leave as null to use the current env map using the supplied allocator.
+env_map: ?*const EnvMap,
+
+stdin_behavior: StdIo,
+stdout_behavior: StdIo,
+stderr_behavior: StdIo,
+
+/// Set to change the user id when spawning the child process.
+uid: if (native_os == .windows or native_os == .wasi) void else ?posix.uid_t,
+
+/// Set to change the group id when spawning the child process.
+gid: if (native_os == .windows or native_os == .wasi) void else ?posix.gid_t,
+
+/// Set to change the current working directory when spawning the child process.
+cwd: ?[]const u8,
+/// Set to change the current working directory when spawning the child process.
+/// This is not yet implemented for Windows. See https://github.com/ziglang/zig/issues/5190
+/// Once that is done, `cwd` will be deprecated in favor of this field.
+cwd_dir: ?fs.Dir = null,
+
+err_pipe: ?if (native_os == .windows) void else [2]posix.fd_t,
+
+expand_arg0: Arg0Expand,
+
+/// Darwin-only. Disable ASLR for the child process.
+disable_aslr: bool = false,
+
+/// Darwin-only. Start child process in suspended state as if SIGSTOP was sent.
+start_suspended: bool = false,
+
+/// Set to true to obtain rusage information for the child process.
+/// Depending on the target platform and implementation status, the
+/// requested statistics may or may not be available. If they are
+/// available, then the `resource_usage_statistics` field will be populated
+/// after calling `wait`.
+/// On Linux and Darwin, this obtains rusage statistics from wait4().
+request_resource_usage_statistics: bool = false,
+
+/// This is available after calling wait if
+/// `request_resource_usage_statistics` was set to `true` before calling
+/// `spawn`.
+resource_usage_statistics: ResourceUsageStatistics = .{},
+
+pub const ResourceUsageStatistics = struct {
+    rusage: @TypeOf(rusage_init) = rusage_init,
+
+    /// Returns the peak resident set size of the child process, in bytes,
+    /// if available.
+    pub inline fn getMaxRss(rus: ResourceUsageStatistics) ?usize {
+        switch (native_os) {
+            .linux => {
+                if (rus.rusage) |ru| {
+                    return @as(usize, @intCast(ru.maxrss)) * 1024;
+                } else {
+                    return null;
+                }
+            },
+            .windows => {
+                if (rus.rusage) |ru| {
+                    return ru.PeakWorkingSetSize;
+                } else {
+                    return null;
+                }
+            },
+            .macos, .ios => {
+                if (rus.rusage) |ru| {
+                    // Darwin oddly reports in bytes instead of kilobytes.
+                    return @as(usize, @intCast(ru.maxrss));
+                } else {
+                    return null;
+                }
+            },
+            else => return null,
+        }
+    }
+
+    const rusage_init = switch (native_os) {
+        .linux, .macos, .ios => @as(?posix.rusage, null),
+        .windows => @as(?windows.VM_COUNTERS, null),
+        else => {},
+    };
+};
+
+pub const Arg0Expand = posix.Arg0Expand;
+
+pub const SpawnError = error{
+    OutOfMemory,
+
+    /// POSIX-only. `StdIo.Ignore` was selected and opening `/dev/null` returned ENODEV.
+    NoDevice,
+
+    /// Windows-only. `cwd` or `argv` was provided and it was invalid WTF-8.
+    /// https://simonsapin.github.io/wtf-8/
+    InvalidWtf8,
+
+    /// Windows-only. `cwd` was provided, but the path did not exist when spawning the child process.
+    CurrentWorkingDirectoryUnlinked,
+
+    /// Windows-only. NUL (U+0000), LF (U+000A), CR (U+000D) are not allowed
+    /// within arguments when executing a `.bat`/`.cmd` script.
+    /// - NUL/LF signifiies end of arguments, so anything afterwards
+    ///   would be lost after execution.
+    /// - CR is stripped by `cmd.exe`, so any CR codepoints
+    ///   would be lost after execution.
+    InvalidBatchScriptArg,
+} ||
+    posix.ExecveError ||
+    posix.SetIdError ||
+    posix.ChangeCurDirError ||
+    windows.CreateProcessError ||
+    windows.GetProcessMemoryInfoError ||
+    windows.WaitForSingleObjectError;
+
+pub const Term = union(enum) {
+    Exited: u8,
+    Signal: u32,
+    Stopped: u32,
+    Unknown: u32,
+};
+
+/// Behavior of the child process's standard input, output, and error
+/// streams.
+pub const StdIo = enum {
+    /// Inherit the stream from the parent process.
+    Inherit,
+
+    /// Pass a null stream to the child process.
+    /// This is /dev/null on POSIX and NUL on Windows.
+    Ignore,
+
+    /// Create a pipe for the stream.
+    /// The corresponding field (`stdout`, `stderr`, or `stdin`)
+    /// will be assigned a `File` object that can be used
+    /// to read from or write to the pipe.
+    Pipe,
+
+    /// Close the stream after the child process spawns.
+    Close,
+};
+
+/// First argument in argv is the executable.
+pub fn init(argv: []const []const u8, allocator: mem.Allocator) ChildProcess {
+    return .{
+        .allocator = allocator,
+        .argv = argv,
+        .id = undefined,
+        .thread_handle = undefined,
+        .err_pipe = null,
+        .term = null,
+        .env_map = null,
+        .cwd = null,
+        .uid = if (native_os == .windows or native_os == .wasi) {} else null,
+        .gid = if (native_os == .windows or native_os == .wasi) {} else null,
+        .stdin = null,
+        .stdout = null,
+        .stderr = null,
+        .stdin_behavior = StdIo.Inherit,
+        .stdout_behavior = StdIo.Inherit,
+        .stderr_behavior = StdIo.Inherit,
+        .expand_arg0 = .no_expand,
+    };
+}
+
+pub fn setUserName(self: *ChildProcess, name: []const u8) !void {
+    const user_info = try process.getUserInfo(name);
+    self.uid = user_info.uid;
+    self.gid = user_info.gid;
+}
+
+/// On success must call `kill` or `wait`.
+/// After spawning the `id` is available.
+pub fn spawn(self: *ChildProcess) SpawnError!void {
+    if (!process.can_spawn) {
+        @compileError("the target operating system cannot spawn processes");
+    }
+
+    if (native_os == .windows) {
+        return self.spawnWindows();
+    } else {
+        return self.spawnPosix();
+    }
+}
+
+pub fn spawnAndWait(self: *ChildProcess) SpawnError!Term {
+    try self.spawn();
+    return self.wait();
+}
+
+/// Forcibly terminates child process and then cleans up all resources.
+pub fn kill(self: *ChildProcess) !Term {
+    if (native_os == .windows) {
+        return self.killWindows(1);
+    } else {
+        return self.killPosix();
+    }
+}
+
+pub fn killWindows(self: *ChildProcess, exit_code: windows.UINT) !Term {
+    if (self.term) |term| {
+        self.cleanupStreams();
+        return term;
+    }
+
+    windows.TerminateProcess(self.id, exit_code) catch |err| switch (err) {
+        error.PermissionDenied => {
+            // Usually when TerminateProcess triggers a ACCESS_DENIED error, it
+            // indicates that the process has already exited, but there may be
+            // some rare edge cases where our process handle no longer has the
+            // PROCESS_TERMINATE access right, so let's do another check to make
+            // sure the process is really no longer running:
+            windows.WaitForSingleObjectEx(self.id, 0, false) catch return err;
+            return error.AlreadyTerminated;
+        },
+        else => return err,
+    };
+    try self.waitUnwrappedWindows();
+    return self.term.?;
+}
+
+pub fn killPosix(self: *ChildProcess) !Term {
+    if (self.term) |term| {
+        self.cleanupStreams();
+        return term;
+    }
+    posix.kill(self.id, posix.SIG.TERM) catch |err| switch (err) {
+        error.ProcessNotFound => return error.AlreadyTerminated,
+        else => return err,
+    };
+    try self.waitUnwrapped();
+    return self.term.?;
+}
+
+/// Blocks until child process terminates and then cleans up all resources.
+pub fn wait(self: *ChildProcess) !Term {
+    const term = if (native_os == .windows)
+        try self.waitWindows()
+    else
+        try self.waitPosix();
+
+    self.id = undefined;
+
+    return term;
+}
+
+pub const RunResult = struct {
+    term: Term,
+    stdout: []u8,
+    stderr: []u8,
+};
+
+fn fifoToOwnedArrayList(fifo: *std.io.PollFifo) std.ArrayList(u8) {
+    if (fifo.head > 0) {
+        @memcpy(fifo.buf[0..fifo.count], fifo.buf[fifo.head..][0..fifo.count]);
+    }
+    const result = std.ArrayList(u8){
+        .items = fifo.buf[0..fifo.count],
+        .capacity = fifo.buf.len,
+        .allocator = fifo.allocator,
+    };
+    fifo.* = std.io.PollFifo.init(fifo.allocator);
+    return result;
+}
+
+/// Collect the output from the process's stdout and stderr. Will return once all output
+/// has been collected. This does not mean that the process has ended. `wait` should still
+/// be called to wait for and clean up the process.
+///
+/// The process must be started with stdout_behavior and stderr_behavior == .Pipe
+pub fn collectOutput(
+    child: ChildProcess,
+    stdout: *std.ArrayList(u8),
+    stderr: *std.ArrayList(u8),
+    max_output_bytes: usize,
+) !void {
+    assert(child.stdout_behavior == .Pipe);
+    assert(child.stderr_behavior == .Pipe);
+
+    // we could make this work with multiple allocators but YAGNI
+    if (stdout.allocator.ptr != stderr.allocator.ptr or
+        stdout.allocator.vtable != stderr.allocator.vtable)
+    {
+        unreachable; // ChildProcess.collectOutput only supports 1 allocator
+    }
+
+    var poller = std.io.poll(stdout.allocator, enum { stdout, stderr }, .{
+        .stdout = child.stdout.?,
+        .stderr = child.stderr.?,
+    });
+    defer poller.deinit();
+
+    while (try poller.poll()) {
+        if (poller.fifo(.stdout).count > max_output_bytes)
+            return error.StdoutStreamTooLong;
+        if (poller.fifo(.stderr).count > max_output_bytes)
+            return error.StderrStreamTooLong;
+    }
+
+    stdout.* = fifoToOwnedArrayList(poller.fifo(.stdout));
+    stderr.* = fifoToOwnedArrayList(poller.fifo(.stderr));
+}
+
+pub const RunError = posix.GetCwdError || posix.ReadError || SpawnError || posix.PollError || error{
+    StdoutStreamTooLong,
+    StderrStreamTooLong,
+};
+
+/// Spawns a child process, waits for it, collecting stdout and stderr, and then returns.
+/// If it succeeds, the caller owns result.stdout and result.stderr memory.
+pub fn run(args: struct {
+    allocator: mem.Allocator,
+    argv: []const []const u8,
+    cwd: ?[]const u8 = null,
+    cwd_dir: ?fs.Dir = null,
+    env_map: ?*const EnvMap = null,
+    max_output_bytes: usize = 50 * 1024,
+    expand_arg0: Arg0Expand = .no_expand,
+}) RunError!RunResult {
+    var child = ChildProcess.init(args.argv, args.allocator);
+    child.stdin_behavior = .Ignore;
+    child.stdout_behavior = .Pipe;
+    child.stderr_behavior = .Pipe;
+    child.cwd = args.cwd;
+    child.cwd_dir = args.cwd_dir;
+    child.env_map = args.env_map;
+    child.expand_arg0 = args.expand_arg0;
+
+    var stdout = std.ArrayList(u8).init(args.allocator);
+    var stderr = std.ArrayList(u8).init(args.allocator);
+    errdefer {
+        stdout.deinit();
+        stderr.deinit();
+    }
+
+    try child.spawn();
+    try child.collectOutput(&stdout, &stderr, args.max_output_bytes);
+
+    return RunResult{
+        .term = try child.wait(),
+        .stdout = try stdout.toOwnedSlice(),
+        .stderr = try stderr.toOwnedSlice(),
+    };
+}
+
+fn waitWindows(self: *ChildProcess) !Term {
+    if (self.term) |term| {
+        self.cleanupStreams();
+        return term;
+    }
+
+    try self.waitUnwrappedWindows();
+    return self.term.?;
+}
+
+fn waitPosix(self: *ChildProcess) !Term {
+    if (self.term) |term| {
+        self.cleanupStreams();
+        return term;
+    }
+
+    try self.waitUnwrapped();
+    return self.term.?;
+}
+
+fn waitUnwrappedWindows(self: *ChildProcess) !void {
+    const result = windows.WaitForSingleObjectEx(self.id, windows.INFINITE, false);
+
+    self.term = @as(SpawnError!Term, x: {
+        var exit_code: windows.DWORD = undefined;
+        if (windows.kernel32.GetExitCodeProcess(self.id, &exit_code) == 0) {
+            break :x Term{ .Unknown = 0 };
+        } else {
+            break :x Term{ .Exited = @as(u8, @truncate(exit_code)) };
+        }
+    });
+
+    if (self.request_resource_usage_statistics) {
+        self.resource_usage_statistics.rusage = try windows.GetProcessMemoryInfo(self.id);
+    }
+
+    posix.close(self.id);
+    posix.close(self.thread_handle);
+    self.cleanupStreams();
+    return result;
+}
+
+fn waitUnwrapped(self: *ChildProcess) !void {
+    const res: posix.WaitPidResult = res: {
+        if (self.request_resource_usage_statistics) {
+            switch (native_os) {
+                .linux, .macos, .ios => {
+                    var ru: posix.rusage = undefined;
+                    const res = posix.wait4(self.id, 0, &ru);
+                    self.resource_usage_statistics.rusage = ru;
+                    break :res res;
+                },
+                else => {},
+            }
+        }
+
+        break :res posix.waitpid(self.id, 0);
+    };
+    const status = res.status;
+    self.cleanupStreams();
+    self.handleWaitResult(status);
+}
+
+fn handleWaitResult(self: *ChildProcess, status: u32) void {
+    self.term = self.cleanupAfterWait(status);
+}
+
+fn cleanupStreams(self: *ChildProcess) void {
+    if (self.stdin) |*stdin| {
+        stdin.close();
+        self.stdin = null;
+    }
+    if (self.stdout) |*stdout| {
+        stdout.close();
+        self.stdout = null;
+    }
+    if (self.stderr) |*stderr| {
+        stderr.close();
+        self.stderr = null;
+    }
+}
+
+fn cleanupAfterWait(self: *ChildProcess, status: u32) !Term {
+    if (self.err_pipe) |err_pipe| {
+        defer destroyPipe(err_pipe);
+
+        if (native_os == .linux) {
+            var fd = [1]posix.pollfd{posix.pollfd{
+                .fd = err_pipe[0],
+                .events = posix.POLL.IN,
+                .revents = undefined,
+            }};
+
+            // Check if the eventfd buffer stores a non-zero value by polling
+            // it, that's the error code returned by the child process.
+            _ = posix.poll(&fd, 0) catch unreachable;
+
+            // According to eventfd(2) the descriptor is readable if the counter
+            // has a value greater than 0
+            if ((fd[0].revents & posix.POLL.IN) != 0) {
+                const err_int = try readIntFd(err_pipe[0]);
+                return @as(SpawnError, @errorCast(@errorFromInt(err_int)));
+            }
+        } else {
+            // Write maxInt(ErrInt) to the write end of the err_pipe. This is after
+            // waitpid, so this write is guaranteed to be after the child
+            // pid potentially wrote an error. This way we can do a blocking
+            // read on the error pipe and either get maxInt(ErrInt) (no error) or
+            // an error code.
+            try writeIntFd(err_pipe[1], maxInt(ErrInt));
+            const err_int = try readIntFd(err_pipe[0]);
+            // Here we potentially return the fork child's error from the parent
+            // pid.
+            if (err_int != maxInt(ErrInt)) {
+                return @as(SpawnError, @errorCast(@errorFromInt(err_int)));
+            }
+        }
+    }
+
+    return statusToTerm(status);
+}
+
+fn statusToTerm(status: u32) Term {
+    return if (posix.W.IFEXITED(status))
+        Term{ .Exited = posix.W.EXITSTATUS(status) }
+    else if (posix.W.IFSIGNALED(status))
+        Term{ .Signal = posix.W.TERMSIG(status) }
+    else if (posix.W.IFSTOPPED(status))
+        Term{ .Stopped = posix.W.STOPSIG(status) }
+    else
+        Term{ .Unknown = status };
+}
+
+fn spawnPosix(self: *ChildProcess) SpawnError!void {
+    const pipe_flags: posix.O = .{};
+    const stdin_pipe = if (self.stdin_behavior == StdIo.Pipe) try posix.pipe2(pipe_flags) else undefined;
+    errdefer if (self.stdin_behavior == StdIo.Pipe) {
+        destroyPipe(stdin_pipe);
+    };
+
+    const stdout_pipe = if (self.stdout_behavior == StdIo.Pipe) try posix.pipe2(pipe_flags) else undefined;
+    errdefer if (self.stdout_behavior == StdIo.Pipe) {
+        destroyPipe(stdout_pipe);
+    };
+
+    const stderr_pipe = if (self.stderr_behavior == StdIo.Pipe) try posix.pipe2(pipe_flags) else undefined;
+    errdefer if (self.stderr_behavior == StdIo.Pipe) {
+        destroyPipe(stderr_pipe);
+    };
+
+    const any_ignore = (self.stdin_behavior == StdIo.Ignore or self.stdout_behavior == StdIo.Ignore or self.stderr_behavior == StdIo.Ignore);
+    const dev_null_fd = if (any_ignore)
+        posix.openZ("/dev/null", .{ .ACCMODE = .RDWR }, 0) catch |err| switch (err) {
+            error.PathAlreadyExists => unreachable,
+            error.NoSpaceLeft => unreachable,
+            error.FileTooBig => unreachable,
+            error.DeviceBusy => unreachable,
+            error.FileLocksNotSupported => unreachable,
+            error.BadPathName => unreachable, // Windows-only
+            error.WouldBlock => unreachable,
+            error.NetworkNotFound => unreachable, // Windows-only
+            else => |e| return e,
+        }
+    else
+        undefined;
+    defer {
+        if (any_ignore) posix.close(dev_null_fd);
+    }
+
+    var arena_allocator = std.heap.ArenaAllocator.init(self.allocator);
+    defer arena_allocator.deinit();
+    const arena = arena_allocator.allocator();
+
+    // The POSIX standard does not allow malloc() between fork() and execve(),
+    // and `self.allocator` may be a libc allocator.
+    // I have personally observed the child process deadlocking when it tries
+    // to call malloc() due to a heap allocation between fork() and execve(),
+    // in musl v1.1.24.
+    // Additionally, we want to reduce the number of possible ways things
+    // can fail between fork() and execve().
+    // Therefore, we do all the allocation for the execve() before the fork().
+    // This means we must do the null-termination of argv and env vars here.
+    const argv_buf = try arena.allocSentinel(?[*:0]const u8, self.argv.len, null);
+    for (self.argv, 0..) |arg, i| argv_buf[i] = (try arena.dupeZ(u8, arg)).ptr;
+
+    const envp = m: {
+        if (self.env_map) |env_map| {
+            const envp_buf = try process.createNullDelimitedEnvMap(arena, env_map);
+            break :m envp_buf.ptr;
+        } else if (builtin.link_libc) {
+            break :m std.c.environ;
+        } else if (builtin.output_mode == .Exe) {
+            // Then we have Zig start code and this works.
+            // TODO type-safety for null-termination of `os.environ`.
+            break :m @as([*:null]const ?[*:0]const u8, @ptrCast(std.os.environ.ptr));
+        } else {
+            // TODO come up with a solution for this.
+            @compileError("missing std lib enhancement: ChildProcess implementation has no way to collect the environment variables to forward to the child process");
+        }
+    };
+
+    // This pipe is used to communicate errors between the time of fork
+    // and execve from the child process to the parent process.
+    const err_pipe = blk: {
+        if (native_os == .linux) {
+            const fd = try posix.eventfd(0, linux.EFD.CLOEXEC);
+            // There's no distinction between the readable and the writeable
+            // end with eventfd
+            break :blk [2]posix.fd_t{ fd, fd };
+        } else {
+            break :blk try posix.pipe2(.{ .CLOEXEC = true });
+        }
+    };
+    errdefer destroyPipe(err_pipe);
+
+    const pid_result = try posix.fork();
+    if (pid_result == 0) {
+        // we are the child
+        setUpChildIo(self.stdin_behavior, stdin_pipe[0], posix.STDIN_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
+        setUpChildIo(self.stdout_behavior, stdout_pipe[1], posix.STDOUT_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
+        setUpChildIo(self.stderr_behavior, stderr_pipe[1], posix.STDERR_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
+
+        if (self.stdin_behavior == .Pipe) {
+            posix.close(stdin_pipe[0]);
+            posix.close(stdin_pipe[1]);
+        }
+        if (self.stdout_behavior == .Pipe) {
+            posix.close(stdout_pipe[0]);
+            posix.close(stdout_pipe[1]);
+        }
+        if (self.stderr_behavior == .Pipe) {
+            posix.close(stderr_pipe[0]);
+            posix.close(stderr_pipe[1]);
+        }
+
+        if (self.cwd_dir) |cwd| {
+            posix.fchdir(cwd.fd) catch |err| forkChildErrReport(err_pipe[1], err);
+        } else if (self.cwd) |cwd| {
+            posix.chdir(cwd) catch |err| forkChildErrReport(err_pipe[1], err);
+        }
+
+        if (self.gid) |gid| {
+            posix.setregid(gid, gid) catch |err| forkChildErrReport(err_pipe[1], err);
+        }
+
+        if (self.uid) |uid| {
+            posix.setreuid(uid, uid) catch |err| forkChildErrReport(err_pipe[1], err);
+        }
+
+        const err = switch (self.expand_arg0) {
+            .expand => posix.execvpeZ_expandArg0(.expand, argv_buf.ptr[0].?, argv_buf.ptr, envp),
+            .no_expand => posix.execvpeZ_expandArg0(.no_expand, argv_buf.ptr[0].?, argv_buf.ptr, envp),
+        };
+        forkChildErrReport(err_pipe[1], err);
+    }
+
+    // we are the parent
+    const pid: i32 = @intCast(pid_result);
+    if (self.stdin_behavior == StdIo.Pipe) {
+        self.stdin = File{ .handle = stdin_pipe[1] };
+    } else {
+        self.stdin = null;
+    }
+    if (self.stdout_behavior == StdIo.Pipe) {
+        self.stdout = File{ .handle = stdout_pipe[0] };
+    } else {
+        self.stdout = null;
+    }
+    if (self.stderr_behavior == StdIo.Pipe) {
+        self.stderr = File{ .handle = stderr_pipe[0] };
+    } else {
+        self.stderr = null;
+    }
+
+    self.id = pid;
+    self.err_pipe = err_pipe;
+    self.term = null;
+
+    if (self.stdin_behavior == StdIo.Pipe) {
+        posix.close(stdin_pipe[0]);
+    }
+    if (self.stdout_behavior == StdIo.Pipe) {
+        posix.close(stdout_pipe[1]);
+    }
+    if (self.stderr_behavior == StdIo.Pipe) {
+        posix.close(stderr_pipe[1]);
+    }
+}
+
+fn spawnWindows(self: *ChildProcess) SpawnError!void {
+    var saAttr = windows.SECURITY_ATTRIBUTES{
+        .nLength = @sizeOf(windows.SECURITY_ATTRIBUTES),
+        .bInheritHandle = windows.TRUE,
+        .lpSecurityDescriptor = null,
+    };
+
+    const any_ignore = (self.stdin_behavior == StdIo.Ignore or self.stdout_behavior == StdIo.Ignore or self.stderr_behavior == StdIo.Ignore);
+
+    const nul_handle = if (any_ignore)
+        // "\Device\Null" or "\??\NUL"
+        windows.OpenFile(&[_]u16{ '\\', 'D', 'e', 'v', 'i', 'c', 'e', '\\', 'N', 'u', 'l', 'l' }, .{
+            .access_mask = windows.GENERIC_READ | windows.GENERIC_WRITE | windows.SYNCHRONIZE,
+            .share_access = windows.FILE_SHARE_READ | windows.FILE_SHARE_WRITE | windows.FILE_SHARE_DELETE,
+            .sa = &saAttr,
+            .creation = windows.OPEN_EXISTING,
+        }) catch |err| switch (err) {
+            error.PathAlreadyExists => return error.Unexpected, // not possible for "NUL"
+            error.PipeBusy => return error.Unexpected, // not possible for "NUL"
+            error.FileNotFound => return error.Unexpected, // not possible for "NUL"
+            error.AccessDenied => return error.Unexpected, // not possible for "NUL"
+            error.NameTooLong => return error.Unexpected, // not possible for "NUL"
+            error.WouldBlock => return error.Unexpected, // not possible for "NUL"
+            error.NetworkNotFound => return error.Unexpected, // not possible for "NUL"
+            error.AntivirusInterference => return error.Unexpected, // not possible for "NUL"
+            else => |e| return e,
+        }
+    else
+        undefined;
+    defer {
+        if (any_ignore) posix.close(nul_handle);
+    }
+
+    var g_hChildStd_IN_Rd: ?windows.HANDLE = null;
+    var g_hChildStd_IN_Wr: ?windows.HANDLE = null;
+    switch (self.stdin_behavior) {
+        StdIo.Pipe => {
+            try windowsMakePipeIn(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr);
+        },
+        StdIo.Ignore => {
+            g_hChildStd_IN_Rd = nul_handle;
+        },
+        StdIo.Inherit => {
+            g_hChildStd_IN_Rd = windows.GetStdHandle(windows.STD_INPUT_HANDLE) catch null;
+        },
+        StdIo.Close => {
+            g_hChildStd_IN_Rd = null;
+        },
+    }
+    errdefer if (self.stdin_behavior == StdIo.Pipe) {
+        windowsDestroyPipe(g_hChildStd_IN_Rd, g_hChildStd_IN_Wr);
+    };
+
+    var g_hChildStd_OUT_Rd: ?windows.HANDLE = null;
+    var g_hChildStd_OUT_Wr: ?windows.HANDLE = null;
+    switch (self.stdout_behavior) {
+        StdIo.Pipe => {
+            try windowsMakeAsyncPipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr);
+        },
+        StdIo.Ignore => {
+            g_hChildStd_OUT_Wr = nul_handle;
+        },
+        StdIo.Inherit => {
+            g_hChildStd_OUT_Wr = windows.GetStdHandle(windows.STD_OUTPUT_HANDLE) catch null;
+        },
+        StdIo.Close => {
+            g_hChildStd_OUT_Wr = null;
+        },
+    }
+    errdefer if (self.stdout_behavior == StdIo.Pipe) {
+        windowsDestroyPipe(g_hChildStd_OUT_Rd, g_hChildStd_OUT_Wr);
+    };
+
+    var g_hChildStd_ERR_Rd: ?windows.HANDLE = null;
+    var g_hChildStd_ERR_Wr: ?windows.HANDLE = null;
+    switch (self.stderr_behavior) {
+        StdIo.Pipe => {
+            try windowsMakeAsyncPipe(&g_hChildStd_ERR_Rd, &g_hChildStd_ERR_Wr, &saAttr);
+        },
+        StdIo.Ignore => {
+            g_hChildStd_ERR_Wr = nul_handle;
+        },
+        StdIo.Inherit => {
+            g_hChildStd_ERR_Wr = windows.GetStdHandle(windows.STD_ERROR_HANDLE) catch null;
+        },
+        StdIo.Close => {
+            g_hChildStd_ERR_Wr = null;
+        },
+    }
+    errdefer if (self.stderr_behavior == StdIo.Pipe) {
+        windowsDestroyPipe(g_hChildStd_ERR_Rd, g_hChildStd_ERR_Wr);
+    };
+
+    var siStartInfo = windows.STARTUPINFOW{
+        .cb = @sizeOf(windows.STARTUPINFOW),
+        .hStdError = g_hChildStd_ERR_Wr,
+        .hStdOutput = g_hChildStd_OUT_Wr,
+        .hStdInput = g_hChildStd_IN_Rd,
+        .dwFlags = windows.STARTF_USESTDHANDLES,
+
+        .lpReserved = null,
+        .lpDesktop = null,
+        .lpTitle = null,
+        .dwX = 0,
+        .dwY = 0,
+        .dwXSize = 0,
+        .dwYSize = 0,
+        .dwXCountChars = 0,
+        .dwYCountChars = 0,
+        .dwFillAttribute = 0,
+        .wShowWindow = 0,
+        .cbReserved2 = 0,
+        .lpReserved2 = null,
+    };
+    var piProcInfo: windows.PROCESS_INFORMATION = undefined;
+
+    const cwd_w = if (self.cwd) |cwd| try unicode.wtf8ToWtf16LeAllocZ(self.allocator, cwd) else null;
+    defer if (cwd_w) |cwd| self.allocator.free(cwd);
+    const cwd_w_ptr = if (cwd_w) |cwd| cwd.ptr else null;
+
+    const maybe_envp_buf = if (self.env_map) |env_map| try process.createWindowsEnvBlock(self.allocator, env_map) else null;
+    defer if (maybe_envp_buf) |envp_buf| self.allocator.free(envp_buf);
+    const envp_ptr = if (maybe_envp_buf) |envp_buf| envp_buf.ptr else null;
+
+    const app_name_wtf8 = self.argv[0];
+    const app_name_is_absolute = fs.path.isAbsolute(app_name_wtf8);
+
+    // the cwd set in ChildProcess is in effect when choosing the executable path
+    // to match posix semantics
+    var cwd_path_w_needs_free = false;
+    const cwd_path_w = x: {
+        // If the app name is absolute, then we need to use its dirname as the cwd
+        if (app_name_is_absolute) {
+            cwd_path_w_needs_free = true;
+            const dir = fs.path.dirname(app_name_wtf8).?;
+            break :x try unicode.wtf8ToWtf16LeAllocZ(self.allocator, dir);
+        } else if (self.cwd) |cwd| {
+            cwd_path_w_needs_free = true;
+            break :x try unicode.wtf8ToWtf16LeAllocZ(self.allocator, cwd);
+        } else {
+            break :x &[_:0]u16{}; // empty for cwd
+        }
+    };
+    defer if (cwd_path_w_needs_free) self.allocator.free(cwd_path_w);
+
+    // If the app name has more than just a filename, then we need to separate that
+    // into the basename and dirname and use the dirname as an addition to the cwd
+    // path. This is because NtQueryDirectoryFile cannot accept FileName params with
+    // path separators.
+    const app_basename_wtf8 = fs.path.basename(app_name_wtf8);
+    // If the app name is absolute, then the cwd will already have the app's dirname in it,
+    // so only populate app_dirname if app name is a relative path with > 0 path separators.
+    const maybe_app_dirname_wtf8 = if (!app_name_is_absolute) fs.path.dirname(app_name_wtf8) else null;
+    const app_dirname_w: ?[:0]u16 = x: {
+        if (maybe_app_dirname_wtf8) |app_dirname_wtf8| {
+            break :x try unicode.wtf8ToWtf16LeAllocZ(self.allocator, app_dirname_wtf8);
+        }
+        break :x null;
+    };
+    defer if (app_dirname_w != null) self.allocator.free(app_dirname_w.?);
+
+    const app_name_w = try unicode.wtf8ToWtf16LeAllocZ(self.allocator, app_basename_wtf8);
+    defer self.allocator.free(app_name_w);
+
+    run: {
+        const PATH: [:0]const u16 = process.getenvW(unicode.utf8ToUtf16LeStringLiteral("PATH")) orelse &[_:0]u16{};
+        const PATHEXT: [:0]const u16 = process.getenvW(unicode.utf8ToUtf16LeStringLiteral("PATHEXT")) orelse &[_:0]u16{};
+
+        // In case the command ends up being a .bat/.cmd script, we need to escape things using the cmd.exe rules
+        // and invoke cmd.exe ourselves in order to mitigate arbitrary command execution from maliciously
+        // constructed arguments.
+        //
+        // We'll need to wait until we're actually trying to run the command to know for sure
+        // if the resolved command has the `.bat` or `.cmd` extension, so we defer actually
+        // serializing the command line until we determine how it should be serialized.
+        var cmd_line_cache = WindowsCommandLineCache.init(self.allocator, self.argv);
+        defer cmd_line_cache.deinit();
+
+        var app_buf = std.ArrayListUnmanaged(u16){};
+        defer app_buf.deinit(self.allocator);
+
+        try app_buf.appendSlice(self.allocator, app_name_w);
+
+        var dir_buf = std.ArrayListUnmanaged(u16){};
+        defer dir_buf.deinit(self.allocator);
+
+        if (cwd_path_w.len > 0) {
+            try dir_buf.appendSlice(self.allocator, cwd_path_w);
+        }
+        if (app_dirname_w) |app_dir| {
+            if (dir_buf.items.len > 0) try dir_buf.append(self.allocator, fs.path.sep);
+            try dir_buf.appendSlice(self.allocator, app_dir);
+        }
+        if (dir_buf.items.len > 0) {
+            // Need to normalize the path, openDirW can't handle things like double backslashes
+            const normalized_len = windows.normalizePath(u16, dir_buf.items) catch return error.BadPathName;
+            dir_buf.shrinkRetainingCapacity(normalized_len);
+        }
+
+        windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, &cmd_line_cache, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo) catch |no_path_err| {
+            const original_err = switch (no_path_err) {
+                // argv[0] contains unsupported characters that will never resolve to a valid exe.
+                error.InvalidArg0 => return error.FileNotFound,
+                error.FileNotFound, error.InvalidExe, error.AccessDenied => |e| e,
+                error.UnrecoverableInvalidExe => return error.InvalidExe,
+                else => |e| return e,
+            };
+
+            // If the app name had path separators, that disallows PATH searching,
+            // and there's no need to search the PATH if the app name is absolute.
+            // We still search the path if the cwd is absolute because of the
+            // "cwd set in ChildProcess is in effect when choosing the executable path
+            // to match posix semantics" behavior--we don't want to skip searching
+            // the PATH just because we were trying to set the cwd of the child process.
+            if (app_dirname_w != null or app_name_is_absolute) {
+                return original_err;
+            }
+
+            var it = mem.tokenizeScalar(u16, PATH, ';');
+            while (it.next()) |search_path| {
+                dir_buf.clearRetainingCapacity();
+                try dir_buf.appendSlice(self.allocator, search_path);
+                // Need to normalize the path, some PATH values can contain things like double
+                // backslashes which openDirW can't handle
+                const normalized_len = windows.normalizePath(u16, dir_buf.items) catch continue;
+                dir_buf.shrinkRetainingCapacity(normalized_len);
+
+                if (windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, &cmd_line_cache, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo)) {
+                    break :run;
+                } else |err| switch (err) {
+                    // argv[0] contains unsupported characters that will never resolve to a valid exe.
+                    error.InvalidArg0 => return error.FileNotFound,
+                    error.FileNotFound, error.AccessDenied, error.InvalidExe => continue,
+                    error.UnrecoverableInvalidExe => return error.InvalidExe,
+                    else => |e| return e,
+                }
+            } else {
+                return original_err;
+            }
+        };
+    }
+
+    if (g_hChildStd_IN_Wr) |h| {
+        self.stdin = File{ .handle = h };
+    } else {
+        self.stdin = null;
+    }
+    if (g_hChildStd_OUT_Rd) |h| {
+        self.stdout = File{ .handle = h };
+    } else {
+        self.stdout = null;
+    }
+    if (g_hChildStd_ERR_Rd) |h| {
+        self.stderr = File{ .handle = h };
+    } else {
+        self.stderr = null;
+    }
+
+    self.id = piProcInfo.hProcess;
+    self.thread_handle = piProcInfo.hThread;
+    self.term = null;
+
+    if (self.stdin_behavior == StdIo.Pipe) {
+        posix.close(g_hChildStd_IN_Rd.?);
+    }
+    if (self.stderr_behavior == StdIo.Pipe) {
+        posix.close(g_hChildStd_ERR_Wr.?);
+    }
+    if (self.stdout_behavior == StdIo.Pipe) {
+        posix.close(g_hChildStd_OUT_Wr.?);
+    }
+}
+
+fn setUpChildIo(stdio: StdIo, pipe_fd: i32, std_fileno: i32, dev_null_fd: i32) !void {
+    switch (stdio) {
+        .Pipe => try posix.dup2(pipe_fd, std_fileno),
+        .Close => posix.close(std_fileno),
+        .Inherit => {},
+        .Ignore => try posix.dup2(dev_null_fd, std_fileno),
+    }
+}
+
+fn destroyPipe(pipe: [2]posix.fd_t) void {
+    posix.close(pipe[0]);
+    if (pipe[0] != pipe[1]) posix.close(pipe[1]);
+}
+
+// Child of fork calls this to report an error to the fork parent.
+// Then the child exits.
+fn forkChildErrReport(fd: i32, err: ChildProcess.SpawnError) noreturn {
+    writeIntFd(fd, @as(ErrInt, @intFromError(err))) catch {};
+    // If we're linking libc, some naughty applications may have registered atexit handlers
+    // which we really do not want to run in the fork child. I caught LLVM doing this and
+    // it caused a deadlock instead of doing an exit syscall. In the words of Avril Lavigne,
+    // "Why'd you have to go and make things so complicated?"
+    if (builtin.link_libc) {
+        // The _exit(2) function does nothing but make the exit syscall, unlike exit(3)
+        std.c._exit(1);
+    }
+    posix.exit(1);
+}
+
+fn writeIntFd(fd: i32, value: ErrInt) !void {
+    const file: File = .{ .handle = fd };
+    file.writer().writeInt(u64, @intCast(value), .little) catch return error.SystemResources;
+}
+
+fn readIntFd(fd: i32) !ErrInt {
+    const file: File = .{ .handle = fd };
+    return @intCast(file.reader().readInt(u64, .little) catch return error.SystemResources);
+}
+
+const ErrInt = std.meta.Int(.unsigned, @sizeOf(anyerror) * 8);
+
+/// Expects `app_buf` to contain exactly the app name, and `dir_buf` to contain exactly the dir path.
+/// After return, `app_buf` will always contain exactly the app name and `dir_buf` will always contain exactly the dir path.
+/// Note: `app_buf` should not contain any leading path separators.
+/// Note: If the dir is the cwd, dir_buf should be empty (len = 0).
+fn windowsCreateProcessPathExt(
+    allocator: mem.Allocator,
+    dir_buf: *std.ArrayListUnmanaged(u16),
+    app_buf: *std.ArrayListUnmanaged(u16),
+    pathext: [:0]const u16,
+    cmd_line_cache: *WindowsCommandLineCache,
+    envp_ptr: ?[*]u16,
+    cwd_ptr: ?[*:0]u16,
+    lpStartupInfo: *windows.STARTUPINFOW,
+    lpProcessInformation: *windows.PROCESS_INFORMATION,
+) !void {
+    const app_name_len = app_buf.items.len;
+    const dir_path_len = dir_buf.items.len;
+
+    if (app_name_len == 0) return error.FileNotFound;
+
+    defer app_buf.shrinkRetainingCapacity(app_name_len);
+    defer dir_buf.shrinkRetainingCapacity(dir_path_len);
+
+    // The name of the game here is to avoid CreateProcessW calls at all costs,
+    // and only ever try calling it when we have a real candidate for execution.
+    // Secondarily, we want to minimize the number of syscalls used when checking
+    // for each PATHEXT-appended version of the app name.
+    //
+    // An overview of the technique used:
+    // - Open the search directory for iteration (either cwd or a path from PATH)
+    // - Use NtQueryDirectoryFile with a wildcard filename of `<app name>*` to
+    //   check if anything that could possibly match either the unappended version
+    //   of the app name or any of the versions with a PATHEXT value appended exists.
+    // - If the wildcard NtQueryDirectoryFile call found nothing, we can exit early
+    //   without needing to use PATHEXT at all.
+    //
+    // This allows us to use a <open dir, NtQueryDirectoryFile, close dir> sequence
+    // for any directory that doesn't contain any possible matches, instead of having
+    // to use a separate look up for each individual filename combination (unappended +
+    // each PATHEXT appended). For directories where the wildcard *does* match something,
+    // we iterate the matches and take note of any that are either the unappended version,
+    // or a version with a supported PATHEXT appended. We then try calling CreateProcessW
+    // with the found versions in the appropriate order.
+
+    var dir = dir: {
+        // needs to be null-terminated
+        try dir_buf.append(allocator, 0);
+        defer dir_buf.shrinkRetainingCapacity(dir_path_len);
+        const dir_path_z = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
+        const prefixed_path = try windows.wToPrefixedFileW(null, dir_path_z);
+        break :dir fs.cwd().openDirW(prefixed_path.span().ptr, .{ .iterate = true }) catch
+            return error.FileNotFound;
+    };
+    defer dir.close();
+
+    // Add wildcard and null-terminator
+    try app_buf.append(allocator, '*');
+    try app_buf.append(allocator, 0);
+    const app_name_wildcard = app_buf.items[0 .. app_buf.items.len - 1 :0];
+
+    // This 2048 is arbitrary, we just want it to be large enough to get multiple FILE_DIRECTORY_INFORMATION entries
+    // returned per NtQueryDirectoryFile call.
+    var file_information_buf: [2048]u8 align(@alignOf(windows.FILE_DIRECTORY_INFORMATION)) = undefined;
+    const file_info_maximum_single_entry_size = @sizeOf(windows.FILE_DIRECTORY_INFORMATION) + (windows.NAME_MAX * 2);
+    if (file_information_buf.len < file_info_maximum_single_entry_size) {
+        @compileError("file_information_buf must be large enough to contain at least one maximum size FILE_DIRECTORY_INFORMATION entry");
+    }
+    var io_status: windows.IO_STATUS_BLOCK = undefined;
+
+    const num_supported_pathext = @typeInfo(CreateProcessSupportedExtension).Enum.fields.len;
+    var pathext_seen = [_]bool{false} ** num_supported_pathext;
+    var any_pathext_seen = false;
+    var unappended_exists = false;
+
+    // Fully iterate the wildcard matches via NtQueryDirectoryFile and take note of all versions
+    // of the app_name we should try to spawn.
+    // Note: This is necessary because the order of the files returned is filesystem-dependent:
+    //       On NTFS, `blah.exe*` will always return `blah.exe` first if it exists.
+    //       On FAT32, it's possible for something like `blah.exe.obj` to be returned first.
+    while (true) {
+        const app_name_len_bytes = std.math.cast(u16, app_name_wildcard.len * 2) orelse return error.NameTooLong;
+        var app_name_unicode_string = windows.UNICODE_STRING{
+            .Length = app_name_len_bytes,
+            .MaximumLength = app_name_len_bytes,
+            .Buffer = @constCast(app_name_wildcard.ptr),
+        };
+        const rc = windows.ntdll.NtQueryDirectoryFile(
+            dir.fd,
+            null,
+            null,
+            null,
+            &io_status,
+            &file_information_buf,
+            file_information_buf.len,
+            .FileDirectoryInformation,
+            windows.FALSE, // single result
+            &app_name_unicode_string,
+            windows.FALSE, // restart iteration
+        );
+
+        // If we get nothing with the wildcard, then we can just bail out
+        // as we know appending PATHEXT will not yield anything.
+        switch (rc) {
+            .SUCCESS => {},
+            .NO_SUCH_FILE => return error.FileNotFound,
+            .NO_MORE_FILES => break,
+            .ACCESS_DENIED => return error.AccessDenied,
+            else => return windows.unexpectedStatus(rc),
+        }
+
+        // According to the docs, this can only happen if there is not enough room in the
+        // buffer to write at least one complete FILE_DIRECTORY_INFORMATION entry.
+        // Therefore, this condition should not be possible to hit with the buffer size we use.
+        std.debug.assert(io_status.Information != 0);
+
+        var it = windows.FileInformationIterator(windows.FILE_DIRECTORY_INFORMATION){ .buf = &file_information_buf };
+        while (it.next()) |info| {
+            // Skip directories
+            if (info.FileAttributes & windows.FILE_ATTRIBUTE_DIRECTORY != 0) continue;
+            const filename = @as([*]u16, @ptrCast(&info.FileName))[0 .. info.FileNameLength / 2];
+            // Because all results start with the app_name since we're using the wildcard `app_name*`,
+            // if the length is equal to app_name then this is an exact match
+            if (filename.len == app_name_len) {
+                // Note: We can't break early here because it's possible that the unappended version
+                //       fails to spawn, in which case we still want to try the PATHEXT appended versions.
+                unappended_exists = true;
+            } else if (windowsCreateProcessSupportsExtension(filename[app_name_len..])) |pathext_ext| {
+                pathext_seen[@intFromEnum(pathext_ext)] = true;
+                any_pathext_seen = true;
+            }
+        }
+    }
+
+    const unappended_err = unappended: {
+        if (unappended_exists) {
+            if (dir_path_len != 0) switch (dir_buf.items[dir_buf.items.len - 1]) {
+                '/', '\\' => {},
+                else => try dir_buf.append(allocator, fs.path.sep),
+            };
+            try dir_buf.appendSlice(allocator, app_buf.items[0..app_name_len]);
+            try dir_buf.append(allocator, 0);
+            const full_app_name = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
+
+            const is_bat_or_cmd = bat_or_cmd: {
+                const app_name = app_buf.items[0..app_name_len];
+                const ext_start = std.mem.lastIndexOfScalar(u16, app_name, '.') orelse break :bat_or_cmd false;
+                const ext = app_name[ext_start..];
+                const ext_enum = windowsCreateProcessSupportsExtension(ext) orelse break :bat_or_cmd false;
+                switch (ext_enum) {
+                    .cmd, .bat => break :bat_or_cmd true,
+                    else => break :bat_or_cmd false,
+                }
+            };
+            const cmd_line_w = if (is_bat_or_cmd)
+                try cmd_line_cache.scriptCommandLine(full_app_name)
+            else
+                try cmd_line_cache.commandLine();
+            const app_name_w = if (is_bat_or_cmd)
+                try cmd_line_cache.cmdExePath()
+            else
+                full_app_name;
+
+            if (windowsCreateProcess(app_name_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
+                return;
+            } else |err| switch (err) {
+                error.FileNotFound,
+                error.AccessDenied,
+                => break :unappended err,
+                error.InvalidExe => {
+                    // On InvalidExe, if the extension of the app name is .exe then
+                    // it's treated as an unrecoverable error. Otherwise, it'll be
+                    // skipped as normal.
+                    const app_name = app_buf.items[0..app_name_len];
+                    const ext_start = std.mem.lastIndexOfScalar(u16, app_name, '.') orelse break :unappended err;
+                    const ext = app_name[ext_start..];
+                    if (windows.eqlIgnoreCaseWTF16(ext, unicode.utf8ToUtf16LeStringLiteral(".EXE"))) {
+                        return error.UnrecoverableInvalidExe;
+                    }
+                    break :unappended err;
+                },
+                else => return err,
+            }
+        }
+        break :unappended error.FileNotFound;
+    };
+
+    if (!any_pathext_seen) return unappended_err;
+
+    // Now try any PATHEXT appended versions that we've seen
+    var ext_it = mem.tokenizeScalar(u16, pathext, ';');
+    while (ext_it.next()) |ext| {
+        const ext_enum = windowsCreateProcessSupportsExtension(ext) orelse continue;
+        if (!pathext_seen[@intFromEnum(ext_enum)]) continue;
+
+        dir_buf.shrinkRetainingCapacity(dir_path_len);
+        if (dir_path_len != 0) switch (dir_buf.items[dir_buf.items.len - 1]) {
+            '/', '\\' => {},
+            else => try dir_buf.append(allocator, fs.path.sep),
+        };
+        try dir_buf.appendSlice(allocator, app_buf.items[0..app_name_len]);
+        try dir_buf.appendSlice(allocator, ext);
+        try dir_buf.append(allocator, 0);
+        const full_app_name = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
+
+        const is_bat_or_cmd = switch (ext_enum) {
+            .cmd, .bat => true,
+            else => false,
+        };
+        const cmd_line_w = if (is_bat_or_cmd)
+            try cmd_line_cache.scriptCommandLine(full_app_name)
+        else
+            try cmd_line_cache.commandLine();
+        const app_name_w = if (is_bat_or_cmd)
+            try cmd_line_cache.cmdExePath()
+        else
+            full_app_name;
+
+        if (windowsCreateProcess(app_name_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
+            return;
+        } else |err| switch (err) {
+            error.FileNotFound => continue,
+            error.AccessDenied => continue,
+            error.InvalidExe => {
+                // On InvalidExe, if the extension of the app name is .exe then
+                // it's treated as an unrecoverable error. Otherwise, it'll be
+                // skipped as normal.
+                if (windows.eqlIgnoreCaseWTF16(ext, unicode.utf8ToUtf16LeStringLiteral(".EXE"))) {
+                    return error.UnrecoverableInvalidExe;
+                }
+                continue;
+            },
+            else => return err,
+        }
+    }
+
+    return unappended_err;
+}
+
+fn windowsCreateProcess(
+    app_name: [*:0]u16,
+    cmd_line: [*:0]u16,
+    envp_ptr: ?[*]u16,
+    cwd_ptr: ?[*:0]u16,
+    lpStartupInfo: *windows.STARTUPINFOW,
+    lpProcessInformation: *windows.PROCESS_INFORMATION,
+) !void {
+    // TODO the docs for environment pointer say:
+    // > A pointer to the environment block for the new process. If this parameter
+    // > is NULL, the new process uses the environment of the calling process.
+    // > ...
+    // > An environment block can contain either Unicode or ANSI characters. If
+    // > the environment block pointed to by lpEnvironment contains Unicode
+    // > characters, be sure that dwCreationFlags includes CREATE_UNICODE_ENVIRONMENT.
+    // > If this parameter is NULL and the environment block of the parent process
+    // > contains Unicode characters, you must also ensure that dwCreationFlags
+    // > includes CREATE_UNICODE_ENVIRONMENT.
+    // This seems to imply that we have to somehow know whether our process parent passed
+    // CREATE_UNICODE_ENVIRONMENT if we want to pass NULL for the environment parameter.
+    // Since we do not know this information that would imply that we must not pass NULL
+    // for the parameter.
+    // However this would imply that programs compiled with -DUNICODE could not pass
+    // environment variables to programs that were not, which seems unlikely.
+    // More investigation is needed.
+    return windows.CreateProcessW(
+        app_name,
+        cmd_line,
+        null,
+        null,
+        windows.TRUE,
+        windows.CREATE_UNICODE_ENVIRONMENT,
+        @as(?*anyopaque, @ptrCast(envp_ptr)),
+        cwd_ptr,
+        lpStartupInfo,
+        lpProcessInformation,
+    );
+}
+
+fn windowsMakePipeIn(rd: *?windows.HANDLE, wr: *?windows.HANDLE, sattr: *const windows.SECURITY_ATTRIBUTES) !void {
+    var rd_h: windows.HANDLE = undefined;
+    var wr_h: windows.HANDLE = undefined;
+    try windows.CreatePipe(&rd_h, &wr_h, sattr);
+    errdefer windowsDestroyPipe(rd_h, wr_h);
+    try windows.SetHandleInformation(wr_h, windows.HANDLE_FLAG_INHERIT, 0);
+    rd.* = rd_h;
+    wr.* = wr_h;
+}
+
+fn windowsDestroyPipe(rd: ?windows.HANDLE, wr: ?windows.HANDLE) void {
+    if (rd) |h| posix.close(h);
+    if (wr) |h| posix.close(h);
+}
+
+fn windowsMakeAsyncPipe(rd: *?windows.HANDLE, wr: *?windows.HANDLE, sattr: *const windows.SECURITY_ATTRIBUTES) !void {
+    var tmp_bufw: [128]u16 = undefined;
+
+    // Anonymous pipes are built upon Named pipes.
+    // https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-createpipe
+    // Asynchronous (overlapped) read and write operations are not supported by anonymous pipes.
+    // https://docs.microsoft.com/en-us/windows/win32/ipc/anonymous-pipe-operations
+    const pipe_path = blk: {
+        var tmp_buf: [128]u8 = undefined;
+        // Forge a random path for the pipe.
+        const pipe_path = std.fmt.bufPrintZ(
+            &tmp_buf,
+            "\\\\.\\pipe\\zig-childprocess-{d}-{d}",
+            .{ windows.GetCurrentProcessId(), pipe_name_counter.fetchAdd(1, .monotonic) },
+        ) catch unreachable;
+        const len = std.unicode.wtf8ToWtf16Le(&tmp_bufw, pipe_path) catch unreachable;
+        tmp_bufw[len] = 0;
+        break :blk tmp_bufw[0..len :0];
+    };
+
+    // Create the read handle that can be used with overlapped IO ops.
+    const read_handle = windows.kernel32.CreateNamedPipeW(
+        pipe_path.ptr,
+        windows.PIPE_ACCESS_INBOUND | windows.FILE_FLAG_OVERLAPPED,
+        windows.PIPE_TYPE_BYTE,
+        1,
+        4096,
+        4096,
+        0,
+        sattr,
+    );
+    if (read_handle == windows.INVALID_HANDLE_VALUE) {
+        switch (windows.kernel32.GetLastError()) {
+            else => |err| return windows.unexpectedError(err),
+        }
+    }
+    errdefer posix.close(read_handle);
+
+    var sattr_copy = sattr.*;
+    const write_handle = windows.kernel32.CreateFileW(
+        pipe_path.ptr,
+        windows.GENERIC_WRITE,
+        0,
+        &sattr_copy,
+        windows.OPEN_EXISTING,
+        windows.FILE_ATTRIBUTE_NORMAL,
+        null,
+    );
+    if (write_handle == windows.INVALID_HANDLE_VALUE) {
+        switch (windows.kernel32.GetLastError()) {
+            else => |err| return windows.unexpectedError(err),
+        }
+    }
+    errdefer posix.close(write_handle);
+
+    try windows.SetHandleInformation(read_handle, windows.HANDLE_FLAG_INHERIT, 0);
+
+    rd.* = read_handle;
+    wr.* = write_handle;
+}
+
+var pipe_name_counter = std.atomic.Value(u32).init(1);
+
+// Should be kept in sync with `windowsCreateProcessSupportsExtension`
+const CreateProcessSupportedExtension = enum {
+    bat,
+    cmd,
+    com,
+    exe,
+};
+
+/// Case-insensitive WTF-16 lookup
+fn windowsCreateProcessSupportsExtension(ext: []const u16) ?CreateProcessSupportedExtension {
+    if (ext.len != 4) return null;
+    const State = enum {
+        start,
+        dot,
+        b,
+        ba,
+        c,
+        cm,
+        co,
+        e,
+        ex,
+    };
+    var state: State = .start;
+    for (ext) |c| switch (state) {
+        .start => switch (c) {
+            '.' => state = .dot,
+            else => return null,
+        },
+        .dot => switch (c) {
+            'b', 'B' => state = .b,
+            'c', 'C' => state = .c,
+            'e', 'E' => state = .e,
+            else => return null,
+        },
+        .b => switch (c) {
+            'a', 'A' => state = .ba,
+            else => return null,
+        },
+        .c => switch (c) {
+            'm', 'M' => state = .cm,
+            'o', 'O' => state = .co,
+            else => return null,
+        },
+        .e => switch (c) {
+            'x', 'X' => state = .ex,
+            else => return null,
+        },
+        .ba => switch (c) {
+            't', 'T' => return .bat,
+            else => return null,
+        },
+        .cm => switch (c) {
+            'd', 'D' => return .cmd,
+            else => return null,
+        },
+        .co => switch (c) {
+            'm', 'M' => return .com,
+            else => return null,
+        },
+        .ex => switch (c) {
+            'e', 'E' => return .exe,
+            else => return null,
+        },
+    };
+    return null;
+}
+
+test windowsCreateProcessSupportsExtension {
+    try std.testing.expectEqual(CreateProcessSupportedExtension.exe, windowsCreateProcessSupportsExtension(&[_]u16{ '.', 'e', 'X', 'e' }).?);
+    try std.testing.expect(windowsCreateProcessSupportsExtension(&[_]u16{ '.', 'e', 'X', 'e', 'c' }) == null);
+}
+
+/// Serializes argv into a WTF-16 encoded command-line string for use with CreateProcessW.
+///
+/// Serialization is done on-demand and the result is cached in order to allow for:
+/// - Only serializing the particular type of command line needed (`.bat`/`.cmd`
+///   command line serialization is different from `.exe`/etc)
+/// - Reusing the serialized command lines if necessary (i.e. if the execution
+///   of a command fails and the PATH is going to be continued to be searched
+///   for more candidates)
+const WindowsCommandLineCache = struct {
+    cmd_line: ?[:0]u16 = null,
+    script_cmd_line: ?[:0]u16 = null,
+    cmd_exe_path: ?[:0]u16 = null,
+    argv: []const []const u8,
+    allocator: mem.Allocator,
+
+    fn init(allocator: mem.Allocator, argv: []const []const u8) WindowsCommandLineCache {
+        return .{
+            .allocator = allocator,
+            .argv = argv,
+        };
+    }
+
+    fn deinit(self: *WindowsCommandLineCache) void {
+        if (self.cmd_line) |cmd_line| self.allocator.free(cmd_line);
+        if (self.script_cmd_line) |script_cmd_line| self.allocator.free(script_cmd_line);
+        if (self.cmd_exe_path) |cmd_exe_path| self.allocator.free(cmd_exe_path);
+    }
+
+    fn commandLine(self: *WindowsCommandLineCache) ![:0]u16 {
+        if (self.cmd_line == null) {
+            self.cmd_line = try argvToCommandLineWindows(self.allocator, self.argv);
+        }
+        return self.cmd_line.?;
+    }
+
+    /// Not cached, since the path to the batch script will change during PATH searching.
+    /// `script_path` should be as qualified as possible, e.g. if the PATH is being searched,
+    /// then script_path should include both the search path and the script filename
+    /// (this allows avoiding cmd.exe having to search the PATH again).
+    fn scriptCommandLine(self: *WindowsCommandLineCache, script_path: []const u16) ![:0]u16 {
+        if (self.script_cmd_line) |v| self.allocator.free(v);
+        self.script_cmd_line = try argvToScriptCommandLineWindows(
+            self.allocator,
+            script_path,
+            self.argv[1..],
+        );
+        return self.script_cmd_line.?;
+    }
+
+    fn cmdExePath(self: *WindowsCommandLineCache) ![:0]u16 {
+        if (self.cmd_exe_path == null) {
+            self.cmd_exe_path = try windowsCmdExePath(self.allocator);
+        }
+        return self.cmd_exe_path.?;
+    }
+};
+
+fn windowsCmdExePath(allocator: mem.Allocator) error{ OutOfMemory, Unexpected }![:0]u16 {
+    var buf = try std.ArrayListUnmanaged(u16).initCapacity(allocator, 128);
+    errdefer buf.deinit(allocator);
+    while (true) {
+        const unused_slice = buf.unusedCapacitySlice();
+        // TODO: Get the system directory from PEB.ReadOnlyStaticServerData
+        const len = windows.kernel32.GetSystemDirectoryW(@ptrCast(unused_slice), @intCast(unused_slice.len));
+        if (len == 0) {
+            switch (windows.kernel32.GetLastError()) {
+                else => |err| return windows.unexpectedError(err),
+            }
+        }
+        if (len > unused_slice.len) {
+            try buf.ensureUnusedCapacity(allocator, len);
+        } else {
+            buf.items.len = len;
+            break;
+        }
+    }
+    switch (buf.items[buf.items.len - 1]) {
+        '/', '\\' => {},
+        else => try buf.append(allocator, fs.path.sep),
+    }
+    try buf.appendSlice(allocator, unicode.utf8ToUtf16LeStringLiteral("cmd.exe"));
+    return try buf.toOwnedSliceSentinel(allocator, 0);
+}
+
+const ArgvToCommandLineError = error{ OutOfMemory, InvalidWtf8, InvalidArg0 };
+
+/// Serializes `argv` to a Windows command-line string suitable for passing to a child process and
+/// parsing by the `CommandLineToArgvW` algorithm. The caller owns the returned slice.
+fn argvToCommandLineWindows(
+    allocator: mem.Allocator,
+    argv: []const []const u8,
+) ArgvToCommandLineError![:0]u16 {
+    var buf = std.ArrayList(u8).init(allocator);
+    defer buf.deinit();
+
+    if (argv.len != 0) {
+        const arg0 = argv[0];
+
+        // The first argument must be quoted if it contains spaces or ASCII control characters
+        // (excluding DEL). It also follows special quoting rules where backslashes have no special
+        // interpretation, which makes it impossible to pass certain first arguments containing
+        // double quotes to a child process without characters from the first argument leaking into
+        // subsequent ones (which could have security implications).
+        //
+        // Empty arguments technically don't need quotes, but we quote them anyway for maximum
+        // compatibility with different implementations of the 'CommandLineToArgvW' algorithm.
+        //
+        // Double quotes are illegal in paths on Windows, so for the sake of simplicity we reject
+        // all first arguments containing double quotes, even ones that we could theoretically
+        // serialize in unquoted form.
+        var needs_quotes = arg0.len == 0;
+        for (arg0) |c| {
+            if (c <= ' ') {
+                needs_quotes = true;
+            } else if (c == '"') {
+                return error.InvalidArg0;
+            }
+        }
+        if (needs_quotes) {
+            try buf.append('"');
+            try buf.appendSlice(arg0);
+            try buf.append('"');
+        } else {
+            try buf.appendSlice(arg0);
+        }
+
+        for (argv[1..]) |arg| {
+            try buf.append(' ');
+
+            // Subsequent arguments must be quoted if they contain spaces, tabs or double quotes,
+            // or if they are empty. For simplicity and for maximum compatibility with different
+            // implementations of the 'CommandLineToArgvW' algorithm, we also quote all ASCII
+            // control characters (again, excluding DEL).
+            needs_quotes = for (arg) |c| {
+                if (c <= ' ' or c == '"') {
+                    break true;
+                }
+            } else arg.len == 0;
+            if (!needs_quotes) {
+                try buf.appendSlice(arg);
+                continue;
+            }
+
+            try buf.append('"');
+            var backslash_count: usize = 0;
+            for (arg) |byte| {
+                switch (byte) {
+                    '\\' => {
+                        backslash_count += 1;
+                    },
+                    '"' => {
+                        try buf.appendNTimes('\\', backslash_count * 2 + 1);
+                        try buf.append('"');
+                        backslash_count = 0;
+                    },
+                    else => {
+                        try buf.appendNTimes('\\', backslash_count);
+                        try buf.append(byte);
+                        backslash_count = 0;
+                    },
+                }
+            }
+            try buf.appendNTimes('\\', backslash_count * 2);
+            try buf.append('"');
+        }
+    }
+
+    return try unicode.wtf8ToWtf16LeAllocZ(allocator, buf.items);
+}
+
+test argvToCommandLineWindows {
+    const t = testArgvToCommandLineWindows;
+
+    try t(&.{
+        \\C:\Program Files\zig\zig.exe
+        ,
+        \\run
+        ,
+        \\.\src\main.zig
+        ,
+        \\-target
+        ,
+        \\x86_64-windows-gnu
+        ,
+        \\-O
+        ,
+        \\ReleaseSafe
+        ,
+        \\--
+        ,
+        \\--emoji=๐Ÿ—ฟ
+        ,
+        \\--eval=new Regex("Dwayne \"The Rock\" Johnson")
+        ,
+    },
+        \\"C:\Program Files\zig\zig.exe" run .\src\main.zig -target x86_64-windows-gnu -O ReleaseSafe -- --emoji=๐Ÿ—ฟ "--eval=new Regex(\"Dwayne \\\"The Rock\\\" Johnson\")"
+    );
+
+    try t(&.{}, "");
+    try t(&.{""}, "\"\"");
+    try t(&.{" "}, "\" \"");
+    try t(&.{"\t"}, "\"\t\"");
+    try t(&.{"\x07"}, "\"\x07\"");
+    try t(&.{"๐ŸฆŽ"}, "๐ŸฆŽ");
+
+    try t(
+        &.{ "zig", "aa aa", "bb\tbb", "cc\ncc", "dd\r\ndd", "ee\x7Fee" },
+        "zig \"aa aa\" \"bb\tbb\" \"cc\ncc\" \"dd\r\ndd\" ee\x7Fee",
+    );
+
+    try t(
+        &.{ "\\\\foo bar\\foo bar\\", "\\\\zig zag\\zig zag\\" },
+        "\"\\\\foo bar\\foo bar\\\" \"\\\\zig zag\\zig zag\\\\\"",
+    );
+
+    try std.testing.expectError(
+        error.InvalidArg0,
+        argvToCommandLineWindows(std.testing.allocator, &.{"\"quotes\"quotes\""}),
+    );
+    try std.testing.expectError(
+        error.InvalidArg0,
+        argvToCommandLineWindows(std.testing.allocator, &.{"quotes\"quotes"}),
+    );
+    try std.testing.expectError(
+        error.InvalidArg0,
+        argvToCommandLineWindows(std.testing.allocator, &.{"q u o t e s \" q u o t e s"}),
+    );
+}
+
+fn testArgvToCommandLineWindows(argv: []const []const u8, expected_cmd_line: []const u8) !void {
+    const cmd_line_w = try argvToCommandLineWindows(std.testing.allocator, argv);
+    defer std.testing.allocator.free(cmd_line_w);
+
+    const cmd_line = try unicode.wtf16LeToWtf8Alloc(std.testing.allocator, cmd_line_w);
+    defer std.testing.allocator.free(cmd_line);
+
+    try std.testing.expectEqualStrings(expected_cmd_line, cmd_line);
+}
+
+const ArgvToScriptCommandLineError = error{
+    OutOfMemory,
+    InvalidWtf8,
+    /// NUL (U+0000), LF (U+000A), CR (U+000D) are not allowed
+    /// within arguments when executing a `.bat`/`.cmd` script.
+    /// - NUL/LF signifiies end of arguments, so anything afterwards
+    ///   would be lost after execution.
+    /// - CR is stripped by `cmd.exe`, so any CR codepoints
+    ///   would be lost after execution.
+    InvalidBatchScriptArg,
+};
+
+/// Serializes `argv` to a Windows command-line string that uses `cmd.exe /c` and `cmd.exe`-specific
+/// escaping rules. The caller owns the returned slice.
+///
+/// Escapes `argv` using the suggested mitigation against arbitrary command execution from:
+/// https://flatt.tech/research/posts/batbadbut-you-cant-securely-execute-commands-on-windows/
+fn argvToScriptCommandLineWindows(
+    allocator: mem.Allocator,
+    /// Path to the `.bat`/`.cmd` script. If this path is relative, it is assumed to be relative to the CWD.
+    /// The script must have been verified to exist at this path before calling this function.
+    script_path: []const u16,
+    /// Arguments, not including the script name itself. Expected to be encoded as WTF-8.
+    script_args: []const []const u8,
+) ArgvToScriptCommandLineError![:0]u16 {
+    var buf = try std.ArrayList(u8).initCapacity(allocator, 64);
+    defer buf.deinit();
+
+    // `/d` disables execution of AutoRun commands.
+    // `/e:ON` and `/v:OFF` are needed for BatBadBut mitigation:
+    // > If delayed expansion is enabled via the registry value DelayedExpansion,
+    // > it must be disabled by explicitly calling cmd.exe with the /V:OFF option.
+    // > Escaping for % requires the command extension to be enabled.
+    // > If itโ€™s disabled via the registry value EnableExtensions, it must be enabled with the /E:ON option.
+    // https://flatt.tech/research/posts/batbadbut-you-cant-securely-execute-commands-on-windows/
+    buf.appendSliceAssumeCapacity("cmd.exe /d /e:ON /v:OFF /c \"");
+
+    // Always quote the path to the script arg
+    buf.appendAssumeCapacity('"');
+    // We always want the path to the batch script to include a path separator in order to
+    // avoid cmd.exe searching the PATH for the script. This is not part of the arbitrary
+    // command execution mitigation, we just know exactly what script we want to execute
+    // at this point, and potentially making cmd.exe re-find it is unnecessary.
+    //
+    // If the script path does not have a path separator, then we know its relative to CWD and
+    // we can just put `.\` in the front.
+    if (mem.indexOfAny(u16, script_path, &[_]u16{ mem.nativeToLittle(u16, '\\'), mem.nativeToLittle(u16, '/') }) == null) {
+        try buf.appendSlice(".\\");
+    }
+    // Note that we don't do any escaping/mitigations for this argument, since the relevant
+    // characters (", %, etc) are illegal in file paths and this function should only be called
+    // with script paths that have been verified to exist.
+    try unicode.wtf16LeToWtf8ArrayList(&buf, script_path);
+    buf.appendAssumeCapacity('"');
+
+    for (script_args) |arg| {
+        // Literal carriage returns get stripped when run through cmd.exe
+        // and NUL/newlines act as 'end of command.' Because of this, it's basically
+        // always a mistake to include these characters in argv, so it's
+        // an error condition in order to ensure that the return of this
+        // function can always roundtrip through cmd.exe.
+        if (std.mem.indexOfAny(u8, arg, "\x00\r\n") != null) {
+            return error.InvalidBatchScriptArg;
+        }
+
+        // Separate args with a space.
+        try buf.append(' ');
+
+        // Need to quote if the argument is empty (otherwise the arg would just be lost)
+        // or if the last character is a `\`, since then something like "%~2" in a .bat
+        // script would cause the closing " to be escaped which we don't want.
+        var needs_quotes = arg.len == 0 or arg[arg.len - 1] == '\\';
+        if (!needs_quotes) {
+            for (arg) |c| {
+                switch (c) {
+                    // Known good characters that don't need to be quoted
+                    'A'...'Z', 'a'...'z', '0'...'9', '#', '$', '*', '+', '-', '.', '/', ':', '?', '@', '\\', '_' => {},
+                    // When in doubt, quote
+                    else => {
+                        needs_quotes = true;
+                        break;
+                    },
+                }
+            }
+        }
+        if (needs_quotes) {
+            try buf.append('"');
+        }
+        var backslashes: usize = 0;
+        for (arg) |c| {
+            switch (c) {
+                '\\' => {
+                    backslashes += 1;
+                },
+                '"' => {
+                    try buf.appendNTimes('\\', backslashes);
+                    try buf.append('"');
+                    backslashes = 0;
+                },
+                // Replace `%` with `%%cd:~,%`.
+                //
+                // cmd.exe allows extracting a substring from an environment
+                // variable with the syntax: `%foo:~<start_index>,<end_index>%`.
+                // Therefore, `%cd:~,%` will always expand to an empty string
+                // since both the start and end index are blank, and it is assumed
+                // that `%cd%` is always available since it is a built-in variable
+                // that corresponds to the current directory.
+                //
+                // This means that replacing `%foo%` with `%%cd:~,%foo%%cd:~,%`
+                // will stop `%foo%` from being expanded and *after* expansion
+                // we'll still be left with `%foo%` (the literal string).
+                '%' => {
+                    // the trailing `%` is appended outside the switch
+                    try buf.appendSlice("%%cd:~,");
+                    backslashes = 0;
+                },
+                else => {
+                    backslashes = 0;
+                },
+            }
+            try buf.append(c);
+        }
+        if (needs_quotes) {
+            try buf.appendNTimes('\\', backslashes);
+            try buf.append('"');
+        }
+    }
+
+    try buf.append('"');
+
+    return try unicode.wtf8ToWtf16LeAllocZ(allocator, buf.items);
+}
lib/std/zig/LibCInstallation.zig
@@ -261,7 +261,7 @@ fn findNativeIncludeDirPosix(self: *LibCInstallation, args: FindNativeOptions) F
         dev_null,
     });
 
-    const run_res = std.ChildProcess.run(.{
+    const run_res = std.process.Child.run(.{
         .allocator = allocator,
         .argv = argv.items,
         .max_output_bytes = 1024 * 1024,
@@ -588,7 +588,7 @@ fn ccPrintFileName(args: CCPrintFileNameOptions) ![:0]u8 {
     try appendCcExe(&argv, skip_cc_env_var);
     try argv.append(arg1);
 
-    const run_res = std.ChildProcess.run(.{
+    const run_res = std.process.Child.run(.{
         .allocator = allocator,
         .argv = argv.items,
         .max_output_bytes = 1024 * 1024,
lib/std/Build.zig
@@ -178,7 +178,7 @@ pub const RunError = error{
     ExitCodeFailure,
     ProcessTerminated,
     ExecNotSupported,
-} || std.ChildProcess.SpawnError;
+} || std.process.Child.SpawnError;
 
 pub const PkgConfigError = error{
     PkgConfigCrashed,
@@ -1719,7 +1719,7 @@ pub fn runAllowFail(
     b: *Build,
     argv: []const []const u8,
     out_code: *u8,
-    stderr_behavior: std.ChildProcess.StdIo,
+    stderr_behavior: std.process.Child.StdIo,
 ) RunError![]u8 {
     assert(argv.len != 0);
 
@@ -1727,7 +1727,7 @@ pub fn runAllowFail(
         return error.ExecNotSupported;
 
     const max_output_size = 400 * 1024;
-    var child = std.ChildProcess.init(argv, b.allocator);
+    var child = std.process.Child.init(argv, b.allocator);
     child.stdin_behavior = .Ignore;
     child.stdout_behavior = .Pipe;
     child.stderr_behavior = stderr_behavior;
lib/std/child_process.zig
@@ -1,1880 +0,0 @@
-const std = @import("std.zig");
-const builtin = @import("builtin");
-const unicode = std.unicode;
-const io = std.io;
-const fs = std.fs;
-const process = std.process;
-const File = std.fs.File;
-const windows = std.os.windows;
-const linux = std.os.linux;
-const posix = std.posix;
-const mem = std.mem;
-const math = std.math;
-const debug = std.debug;
-const EnvMap = process.EnvMap;
-const maxInt = std.math.maxInt;
-const assert = std.debug.assert;
-const native_os = builtin.os.tag;
-
-pub const ChildProcess = struct {
-    pub const Id = switch (native_os) {
-        .windows => windows.HANDLE,
-        .wasi => void,
-        else => posix.pid_t,
-    };
-
-    /// Available after calling `spawn()`. This becomes `undefined` after calling `wait()`.
-    /// On Windows this is the hProcess.
-    /// On POSIX this is the pid.
-    id: Id,
-    thread_handle: if (native_os == .windows) windows.HANDLE else void,
-
-    allocator: mem.Allocator,
-
-    /// The writing end of the child process's standard input pipe.
-    /// Usage requires `stdin_behavior == StdIo.Pipe`.
-    /// Available after calling `spawn()`.
-    stdin: ?File,
-
-    /// The reading end of the child process's standard output pipe.
-    /// Usage requires `stdout_behavior == StdIo.Pipe`.
-    /// Available after calling `spawn()`.
-    stdout: ?File,
-
-    /// The reading end of the child process's standard error pipe.
-    /// Usage requires `stderr_behavior == StdIo.Pipe`.
-    /// Available after calling `spawn()`.
-    stderr: ?File,
-
-    /// Terminated state of the child process.
-    /// Available after calling `wait()`.
-    term: ?(SpawnError!Term),
-
-    argv: []const []const u8,
-
-    /// Leave as null to use the current env map using the supplied allocator.
-    env_map: ?*const EnvMap,
-
-    stdin_behavior: StdIo,
-    stdout_behavior: StdIo,
-    stderr_behavior: StdIo,
-
-    /// Set to change the user id when spawning the child process.
-    uid: if (native_os == .windows or native_os == .wasi) void else ?posix.uid_t,
-
-    /// Set to change the group id when spawning the child process.
-    gid: if (native_os == .windows or native_os == .wasi) void else ?posix.gid_t,
-
-    /// Set to change the current working directory when spawning the child process.
-    cwd: ?[]const u8,
-    /// Set to change the current working directory when spawning the child process.
-    /// This is not yet implemented for Windows. See https://github.com/ziglang/zig/issues/5190
-    /// Once that is done, `cwd` will be deprecated in favor of this field.
-    cwd_dir: ?fs.Dir = null,
-
-    err_pipe: ?if (native_os == .windows) void else [2]posix.fd_t,
-
-    expand_arg0: Arg0Expand,
-
-    /// Darwin-only. Disable ASLR for the child process.
-    disable_aslr: bool = false,
-
-    /// Darwin-only. Start child process in suspended state as if SIGSTOP was sent.
-    start_suspended: bool = false,
-
-    /// Set to true to obtain rusage information for the child process.
-    /// Depending on the target platform and implementation status, the
-    /// requested statistics may or may not be available. If they are
-    /// available, then the `resource_usage_statistics` field will be populated
-    /// after calling `wait`.
-    /// On Linux and Darwin, this obtains rusage statistics from wait4().
-    request_resource_usage_statistics: bool = false,
-
-    /// This is available after calling wait if
-    /// `request_resource_usage_statistics` was set to `true` before calling
-    /// `spawn`.
-    resource_usage_statistics: ResourceUsageStatistics = .{},
-
-    pub const ResourceUsageStatistics = struct {
-        rusage: @TypeOf(rusage_init) = rusage_init,
-
-        /// Returns the peak resident set size of the child process, in bytes,
-        /// if available.
-        pub inline fn getMaxRss(rus: ResourceUsageStatistics) ?usize {
-            switch (native_os) {
-                .linux => {
-                    if (rus.rusage) |ru| {
-                        return @as(usize, @intCast(ru.maxrss)) * 1024;
-                    } else {
-                        return null;
-                    }
-                },
-                .windows => {
-                    if (rus.rusage) |ru| {
-                        return ru.PeakWorkingSetSize;
-                    } else {
-                        return null;
-                    }
-                },
-                .macos, .ios => {
-                    if (rus.rusage) |ru| {
-                        // Darwin oddly reports in bytes instead of kilobytes.
-                        return @as(usize, @intCast(ru.maxrss));
-                    } else {
-                        return null;
-                    }
-                },
-                else => return null,
-            }
-        }
-
-        const rusage_init = switch (native_os) {
-            .linux, .macos, .ios => @as(?posix.rusage, null),
-            .windows => @as(?windows.VM_COUNTERS, null),
-            else => {},
-        };
-    };
-
-    pub const Arg0Expand = posix.Arg0Expand;
-
-    pub const SpawnError = error{
-        OutOfMemory,
-
-        /// POSIX-only. `StdIo.Ignore` was selected and opening `/dev/null` returned ENODEV.
-        NoDevice,
-
-        /// Windows-only. `cwd` or `argv` was provided and it was invalid WTF-8.
-        /// https://simonsapin.github.io/wtf-8/
-        InvalidWtf8,
-
-        /// Windows-only. `cwd` was provided, but the path did not exist when spawning the child process.
-        CurrentWorkingDirectoryUnlinked,
-
-        /// Windows-only. NUL (U+0000), LF (U+000A), CR (U+000D) are not allowed
-        /// within arguments when executing a `.bat`/`.cmd` script.
-        /// - NUL/LF signifiies end of arguments, so anything afterwards
-        ///   would be lost after execution.
-        /// - CR is stripped by `cmd.exe`, so any CR codepoints
-        ///   would be lost after execution.
-        InvalidBatchScriptArg,
-    } ||
-        posix.ExecveError ||
-        posix.SetIdError ||
-        posix.ChangeCurDirError ||
-        windows.CreateProcessError ||
-        windows.GetProcessMemoryInfoError ||
-        windows.WaitForSingleObjectError;
-
-    pub const Term = union(enum) {
-        Exited: u8,
-        Signal: u32,
-        Stopped: u32,
-        Unknown: u32,
-    };
-
-    /// Behavior of the child process's standard input, output, and error
-    /// streams.
-    pub const StdIo = enum {
-        /// Inherit the stream from the parent process.
-        Inherit,
-
-        /// Pass a null stream to the child process.
-        /// This is /dev/null on POSIX and NUL on Windows.
-        Ignore,
-
-        /// Create a pipe for the stream.
-        /// The corresponding field (`stdout`, `stderr`, or `stdin`)
-        /// will be assigned a `File` object that can be used
-        /// to read from or write to the pipe.
-        Pipe,
-
-        /// Close the stream after the child process spawns.
-        Close,
-    };
-
-    /// First argument in argv is the executable.
-    pub fn init(argv: []const []const u8, allocator: mem.Allocator) ChildProcess {
-        return .{
-            .allocator = allocator,
-            .argv = argv,
-            .id = undefined,
-            .thread_handle = undefined,
-            .err_pipe = null,
-            .term = null,
-            .env_map = null,
-            .cwd = null,
-            .uid = if (native_os == .windows or native_os == .wasi) {} else null,
-            .gid = if (native_os == .windows or native_os == .wasi) {} else null,
-            .stdin = null,
-            .stdout = null,
-            .stderr = null,
-            .stdin_behavior = StdIo.Inherit,
-            .stdout_behavior = StdIo.Inherit,
-            .stderr_behavior = StdIo.Inherit,
-            .expand_arg0 = .no_expand,
-        };
-    }
-
-    pub fn setUserName(self: *ChildProcess, name: []const u8) !void {
-        const user_info = try std.process.getUserInfo(name);
-        self.uid = user_info.uid;
-        self.gid = user_info.gid;
-    }
-
-    /// On success must call `kill` or `wait`.
-    /// After spawning the `id` is available.
-    pub fn spawn(self: *ChildProcess) SpawnError!void {
-        if (!std.process.can_spawn) {
-            @compileError("the target operating system cannot spawn processes");
-        }
-
-        if (native_os == .windows) {
-            return self.spawnWindows();
-        } else {
-            return self.spawnPosix();
-        }
-    }
-
-    pub fn spawnAndWait(self: *ChildProcess) SpawnError!Term {
-        try self.spawn();
-        return self.wait();
-    }
-
-    /// Forcibly terminates child process and then cleans up all resources.
-    pub fn kill(self: *ChildProcess) !Term {
-        if (native_os == .windows) {
-            return self.killWindows(1);
-        } else {
-            return self.killPosix();
-        }
-    }
-
-    pub fn killWindows(self: *ChildProcess, exit_code: windows.UINT) !Term {
-        if (self.term) |term| {
-            self.cleanupStreams();
-            return term;
-        }
-
-        windows.TerminateProcess(self.id, exit_code) catch |err| switch (err) {
-            error.PermissionDenied => {
-                // Usually when TerminateProcess triggers a ACCESS_DENIED error, it
-                // indicates that the process has already exited, but there may be
-                // some rare edge cases where our process handle no longer has the
-                // PROCESS_TERMINATE access right, so let's do another check to make
-                // sure the process is really no longer running:
-                windows.WaitForSingleObjectEx(self.id, 0, false) catch return err;
-                return error.AlreadyTerminated;
-            },
-            else => return err,
-        };
-        try self.waitUnwrappedWindows();
-        return self.term.?;
-    }
-
-    pub fn killPosix(self: *ChildProcess) !Term {
-        if (self.term) |term| {
-            self.cleanupStreams();
-            return term;
-        }
-        posix.kill(self.id, posix.SIG.TERM) catch |err| switch (err) {
-            error.ProcessNotFound => return error.AlreadyTerminated,
-            else => return err,
-        };
-        try self.waitUnwrapped();
-        return self.term.?;
-    }
-
-    /// Blocks until child process terminates and then cleans up all resources.
-    pub fn wait(self: *ChildProcess) !Term {
-        const term = if (native_os == .windows)
-            try self.waitWindows()
-        else
-            try self.waitPosix();
-
-        self.id = undefined;
-
-        return term;
-    }
-
-    pub const RunResult = struct {
-        term: Term,
-        stdout: []u8,
-        stderr: []u8,
-    };
-
-    fn fifoToOwnedArrayList(fifo: *std.io.PollFifo) std.ArrayList(u8) {
-        if (fifo.head > 0) {
-            @memcpy(fifo.buf[0..fifo.count], fifo.buf[fifo.head..][0..fifo.count]);
-        }
-        const result = std.ArrayList(u8){
-            .items = fifo.buf[0..fifo.count],
-            .capacity = fifo.buf.len,
-            .allocator = fifo.allocator,
-        };
-        fifo.* = std.io.PollFifo.init(fifo.allocator);
-        return result;
-    }
-
-    /// Collect the output from the process's stdout and stderr. Will return once all output
-    /// has been collected. This does not mean that the process has ended. `wait` should still
-    /// be called to wait for and clean up the process.
-    ///
-    /// The process must be started with stdout_behavior and stderr_behavior == .Pipe
-    pub fn collectOutput(
-        child: ChildProcess,
-        stdout: *std.ArrayList(u8),
-        stderr: *std.ArrayList(u8),
-        max_output_bytes: usize,
-    ) !void {
-        debug.assert(child.stdout_behavior == .Pipe);
-        debug.assert(child.stderr_behavior == .Pipe);
-
-        // we could make this work with multiple allocators but YAGNI
-        if (stdout.allocator.ptr != stderr.allocator.ptr or
-            stdout.allocator.vtable != stderr.allocator.vtable)
-        {
-            unreachable; // ChildProcess.collectOutput only supports 1 allocator
-        }
-
-        var poller = std.io.poll(stdout.allocator, enum { stdout, stderr }, .{
-            .stdout = child.stdout.?,
-            .stderr = child.stderr.?,
-        });
-        defer poller.deinit();
-
-        while (try poller.poll()) {
-            if (poller.fifo(.stdout).count > max_output_bytes)
-                return error.StdoutStreamTooLong;
-            if (poller.fifo(.stderr).count > max_output_bytes)
-                return error.StderrStreamTooLong;
-        }
-
-        stdout.* = fifoToOwnedArrayList(poller.fifo(.stdout));
-        stderr.* = fifoToOwnedArrayList(poller.fifo(.stderr));
-    }
-
-    pub const RunError = posix.GetCwdError || posix.ReadError || SpawnError || posix.PollError || error{
-        StdoutStreamTooLong,
-        StderrStreamTooLong,
-    };
-
-    /// Spawns a child process, waits for it, collecting stdout and stderr, and then returns.
-    /// If it succeeds, the caller owns result.stdout and result.stderr memory.
-    pub fn run(args: struct {
-        allocator: mem.Allocator,
-        argv: []const []const u8,
-        cwd: ?[]const u8 = null,
-        cwd_dir: ?fs.Dir = null,
-        env_map: ?*const EnvMap = null,
-        max_output_bytes: usize = 50 * 1024,
-        expand_arg0: Arg0Expand = .no_expand,
-    }) RunError!RunResult {
-        var child = ChildProcess.init(args.argv, args.allocator);
-        child.stdin_behavior = .Ignore;
-        child.stdout_behavior = .Pipe;
-        child.stderr_behavior = .Pipe;
-        child.cwd = args.cwd;
-        child.cwd_dir = args.cwd_dir;
-        child.env_map = args.env_map;
-        child.expand_arg0 = args.expand_arg0;
-
-        var stdout = std.ArrayList(u8).init(args.allocator);
-        var stderr = std.ArrayList(u8).init(args.allocator);
-        errdefer {
-            stdout.deinit();
-            stderr.deinit();
-        }
-
-        try child.spawn();
-        try child.collectOutput(&stdout, &stderr, args.max_output_bytes);
-
-        return RunResult{
-            .term = try child.wait(),
-            .stdout = try stdout.toOwnedSlice(),
-            .stderr = try stderr.toOwnedSlice(),
-        };
-    }
-
-    fn waitWindows(self: *ChildProcess) !Term {
-        if (self.term) |term| {
-            self.cleanupStreams();
-            return term;
-        }
-
-        try self.waitUnwrappedWindows();
-        return self.term.?;
-    }
-
-    fn waitPosix(self: *ChildProcess) !Term {
-        if (self.term) |term| {
-            self.cleanupStreams();
-            return term;
-        }
-
-        try self.waitUnwrapped();
-        return self.term.?;
-    }
-
-    fn waitUnwrappedWindows(self: *ChildProcess) !void {
-        const result = windows.WaitForSingleObjectEx(self.id, windows.INFINITE, false);
-
-        self.term = @as(SpawnError!Term, x: {
-            var exit_code: windows.DWORD = undefined;
-            if (windows.kernel32.GetExitCodeProcess(self.id, &exit_code) == 0) {
-                break :x Term{ .Unknown = 0 };
-            } else {
-                break :x Term{ .Exited = @as(u8, @truncate(exit_code)) };
-            }
-        });
-
-        if (self.request_resource_usage_statistics) {
-            self.resource_usage_statistics.rusage = try windows.GetProcessMemoryInfo(self.id);
-        }
-
-        posix.close(self.id);
-        posix.close(self.thread_handle);
-        self.cleanupStreams();
-        return result;
-    }
-
-    fn waitUnwrapped(self: *ChildProcess) !void {
-        const res: posix.WaitPidResult = res: {
-            if (self.request_resource_usage_statistics) {
-                switch (native_os) {
-                    .linux, .macos, .ios => {
-                        var ru: posix.rusage = undefined;
-                        const res = posix.wait4(self.id, 0, &ru);
-                        self.resource_usage_statistics.rusage = ru;
-                        break :res res;
-                    },
-                    else => {},
-                }
-            }
-
-            break :res posix.waitpid(self.id, 0);
-        };
-        const status = res.status;
-        self.cleanupStreams();
-        self.handleWaitResult(status);
-    }
-
-    fn handleWaitResult(self: *ChildProcess, status: u32) void {
-        self.term = self.cleanupAfterWait(status);
-    }
-
-    fn cleanupStreams(self: *ChildProcess) void {
-        if (self.stdin) |*stdin| {
-            stdin.close();
-            self.stdin = null;
-        }
-        if (self.stdout) |*stdout| {
-            stdout.close();
-            self.stdout = null;
-        }
-        if (self.stderr) |*stderr| {
-            stderr.close();
-            self.stderr = null;
-        }
-    }
-
-    fn cleanupAfterWait(self: *ChildProcess, status: u32) !Term {
-        if (self.err_pipe) |err_pipe| {
-            defer destroyPipe(err_pipe);
-
-            if (native_os == .linux) {
-                var fd = [1]posix.pollfd{posix.pollfd{
-                    .fd = err_pipe[0],
-                    .events = posix.POLL.IN,
-                    .revents = undefined,
-                }};
-
-                // Check if the eventfd buffer stores a non-zero value by polling
-                // it, that's the error code returned by the child process.
-                _ = posix.poll(&fd, 0) catch unreachable;
-
-                // According to eventfd(2) the descriptor is readable if the counter
-                // has a value greater than 0
-                if ((fd[0].revents & posix.POLL.IN) != 0) {
-                    const err_int = try readIntFd(err_pipe[0]);
-                    return @as(SpawnError, @errorCast(@errorFromInt(err_int)));
-                }
-            } else {
-                // Write maxInt(ErrInt) to the write end of the err_pipe. This is after
-                // waitpid, so this write is guaranteed to be after the child
-                // pid potentially wrote an error. This way we can do a blocking
-                // read on the error pipe and either get maxInt(ErrInt) (no error) or
-                // an error code.
-                try writeIntFd(err_pipe[1], maxInt(ErrInt));
-                const err_int = try readIntFd(err_pipe[0]);
-                // Here we potentially return the fork child's error from the parent
-                // pid.
-                if (err_int != maxInt(ErrInt)) {
-                    return @as(SpawnError, @errorCast(@errorFromInt(err_int)));
-                }
-            }
-        }
-
-        return statusToTerm(status);
-    }
-
-    fn statusToTerm(status: u32) Term {
-        return if (posix.W.IFEXITED(status))
-            Term{ .Exited = posix.W.EXITSTATUS(status) }
-        else if (posix.W.IFSIGNALED(status))
-            Term{ .Signal = posix.W.TERMSIG(status) }
-        else if (posix.W.IFSTOPPED(status))
-            Term{ .Stopped = posix.W.STOPSIG(status) }
-        else
-            Term{ .Unknown = status };
-    }
-
-    fn spawnPosix(self: *ChildProcess) SpawnError!void {
-        const pipe_flags: posix.O = .{};
-        const stdin_pipe = if (self.stdin_behavior == StdIo.Pipe) try posix.pipe2(pipe_flags) else undefined;
-        errdefer if (self.stdin_behavior == StdIo.Pipe) {
-            destroyPipe(stdin_pipe);
-        };
-
-        const stdout_pipe = if (self.stdout_behavior == StdIo.Pipe) try posix.pipe2(pipe_flags) else undefined;
-        errdefer if (self.stdout_behavior == StdIo.Pipe) {
-            destroyPipe(stdout_pipe);
-        };
-
-        const stderr_pipe = if (self.stderr_behavior == StdIo.Pipe) try posix.pipe2(pipe_flags) else undefined;
-        errdefer if (self.stderr_behavior == StdIo.Pipe) {
-            destroyPipe(stderr_pipe);
-        };
-
-        const any_ignore = (self.stdin_behavior == StdIo.Ignore or self.stdout_behavior == StdIo.Ignore or self.stderr_behavior == StdIo.Ignore);
-        const dev_null_fd = if (any_ignore)
-            posix.openZ("/dev/null", .{ .ACCMODE = .RDWR }, 0) catch |err| switch (err) {
-                error.PathAlreadyExists => unreachable,
-                error.NoSpaceLeft => unreachable,
-                error.FileTooBig => unreachable,
-                error.DeviceBusy => unreachable,
-                error.FileLocksNotSupported => unreachable,
-                error.BadPathName => unreachable, // Windows-only
-                error.WouldBlock => unreachable,
-                error.NetworkNotFound => unreachable, // Windows-only
-                else => |e| return e,
-            }
-        else
-            undefined;
-        defer {
-            if (any_ignore) posix.close(dev_null_fd);
-        }
-
-        var arena_allocator = std.heap.ArenaAllocator.init(self.allocator);
-        defer arena_allocator.deinit();
-        const arena = arena_allocator.allocator();
-
-        // The POSIX standard does not allow malloc() between fork() and execve(),
-        // and `self.allocator` may be a libc allocator.
-        // I have personally observed the child process deadlocking when it tries
-        // to call malloc() due to a heap allocation between fork() and execve(),
-        // in musl v1.1.24.
-        // Additionally, we want to reduce the number of possible ways things
-        // can fail between fork() and execve().
-        // Therefore, we do all the allocation for the execve() before the fork().
-        // This means we must do the null-termination of argv and env vars here.
-        const argv_buf = try arena.allocSentinel(?[*:0]const u8, self.argv.len, null);
-        for (self.argv, 0..) |arg, i| argv_buf[i] = (try arena.dupeZ(u8, arg)).ptr;
-
-        const envp = m: {
-            if (self.env_map) |env_map| {
-                const envp_buf = try createNullDelimitedEnvMap(arena, env_map);
-                break :m envp_buf.ptr;
-            } else if (builtin.link_libc) {
-                break :m std.c.environ;
-            } else if (builtin.output_mode == .Exe) {
-                // Then we have Zig start code and this works.
-                // TODO type-safety for null-termination of `os.environ`.
-                break :m @as([*:null]const ?[*:0]const u8, @ptrCast(std.os.environ.ptr));
-            } else {
-                // TODO come up with a solution for this.
-                @compileError("missing std lib enhancement: ChildProcess implementation has no way to collect the environment variables to forward to the child process");
-            }
-        };
-
-        // This pipe is used to communicate errors between the time of fork
-        // and execve from the child process to the parent process.
-        const err_pipe = blk: {
-            if (native_os == .linux) {
-                const fd = try posix.eventfd(0, linux.EFD.CLOEXEC);
-                // There's no distinction between the readable and the writeable
-                // end with eventfd
-                break :blk [2]posix.fd_t{ fd, fd };
-            } else {
-                break :blk try posix.pipe2(.{ .CLOEXEC = true });
-            }
-        };
-        errdefer destroyPipe(err_pipe);
-
-        const pid_result = try posix.fork();
-        if (pid_result == 0) {
-            // we are the child
-            setUpChildIo(self.stdin_behavior, stdin_pipe[0], posix.STDIN_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
-            setUpChildIo(self.stdout_behavior, stdout_pipe[1], posix.STDOUT_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
-            setUpChildIo(self.stderr_behavior, stderr_pipe[1], posix.STDERR_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
-
-            if (self.stdin_behavior == .Pipe) {
-                posix.close(stdin_pipe[0]);
-                posix.close(stdin_pipe[1]);
-            }
-            if (self.stdout_behavior == .Pipe) {
-                posix.close(stdout_pipe[0]);
-                posix.close(stdout_pipe[1]);
-            }
-            if (self.stderr_behavior == .Pipe) {
-                posix.close(stderr_pipe[0]);
-                posix.close(stderr_pipe[1]);
-            }
-
-            if (self.cwd_dir) |cwd| {
-                posix.fchdir(cwd.fd) catch |err| forkChildErrReport(err_pipe[1], err);
-            } else if (self.cwd) |cwd| {
-                posix.chdir(cwd) catch |err| forkChildErrReport(err_pipe[1], err);
-            }
-
-            if (self.gid) |gid| {
-                posix.setregid(gid, gid) catch |err| forkChildErrReport(err_pipe[1], err);
-            }
-
-            if (self.uid) |uid| {
-                posix.setreuid(uid, uid) catch |err| forkChildErrReport(err_pipe[1], err);
-            }
-
-            const err = switch (self.expand_arg0) {
-                .expand => posix.execvpeZ_expandArg0(.expand, argv_buf.ptr[0].?, argv_buf.ptr, envp),
-                .no_expand => posix.execvpeZ_expandArg0(.no_expand, argv_buf.ptr[0].?, argv_buf.ptr, envp),
-            };
-            forkChildErrReport(err_pipe[1], err);
-        }
-
-        // we are the parent
-        const pid: i32 = @intCast(pid_result);
-        if (self.stdin_behavior == StdIo.Pipe) {
-            self.stdin = File{ .handle = stdin_pipe[1] };
-        } else {
-            self.stdin = null;
-        }
-        if (self.stdout_behavior == StdIo.Pipe) {
-            self.stdout = File{ .handle = stdout_pipe[0] };
-        } else {
-            self.stdout = null;
-        }
-        if (self.stderr_behavior == StdIo.Pipe) {
-            self.stderr = File{ .handle = stderr_pipe[0] };
-        } else {
-            self.stderr = null;
-        }
-
-        self.id = pid;
-        self.err_pipe = err_pipe;
-        self.term = null;
-
-        if (self.stdin_behavior == StdIo.Pipe) {
-            posix.close(stdin_pipe[0]);
-        }
-        if (self.stdout_behavior == StdIo.Pipe) {
-            posix.close(stdout_pipe[1]);
-        }
-        if (self.stderr_behavior == StdIo.Pipe) {
-            posix.close(stderr_pipe[1]);
-        }
-    }
-
-    fn spawnWindows(self: *ChildProcess) SpawnError!void {
-        var saAttr = windows.SECURITY_ATTRIBUTES{
-            .nLength = @sizeOf(windows.SECURITY_ATTRIBUTES),
-            .bInheritHandle = windows.TRUE,
-            .lpSecurityDescriptor = null,
-        };
-
-        const any_ignore = (self.stdin_behavior == StdIo.Ignore or self.stdout_behavior == StdIo.Ignore or self.stderr_behavior == StdIo.Ignore);
-
-        const nul_handle = if (any_ignore)
-            // "\Device\Null" or "\??\NUL"
-            windows.OpenFile(&[_]u16{ '\\', 'D', 'e', 'v', 'i', 'c', 'e', '\\', 'N', 'u', 'l', 'l' }, .{
-                .access_mask = windows.GENERIC_READ | windows.GENERIC_WRITE | windows.SYNCHRONIZE,
-                .share_access = windows.FILE_SHARE_READ | windows.FILE_SHARE_WRITE | windows.FILE_SHARE_DELETE,
-                .sa = &saAttr,
-                .creation = windows.OPEN_EXISTING,
-            }) catch |err| switch (err) {
-                error.PathAlreadyExists => return error.Unexpected, // not possible for "NUL"
-                error.PipeBusy => return error.Unexpected, // not possible for "NUL"
-                error.FileNotFound => return error.Unexpected, // not possible for "NUL"
-                error.AccessDenied => return error.Unexpected, // not possible for "NUL"
-                error.NameTooLong => return error.Unexpected, // not possible for "NUL"
-                error.WouldBlock => return error.Unexpected, // not possible for "NUL"
-                error.NetworkNotFound => return error.Unexpected, // not possible for "NUL"
-                error.AntivirusInterference => return error.Unexpected, // not possible for "NUL"
-                else => |e| return e,
-            }
-        else
-            undefined;
-        defer {
-            if (any_ignore) posix.close(nul_handle);
-        }
-
-        var g_hChildStd_IN_Rd: ?windows.HANDLE = null;
-        var g_hChildStd_IN_Wr: ?windows.HANDLE = null;
-        switch (self.stdin_behavior) {
-            StdIo.Pipe => {
-                try windowsMakePipeIn(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr);
-            },
-            StdIo.Ignore => {
-                g_hChildStd_IN_Rd = nul_handle;
-            },
-            StdIo.Inherit => {
-                g_hChildStd_IN_Rd = windows.GetStdHandle(windows.STD_INPUT_HANDLE) catch null;
-            },
-            StdIo.Close => {
-                g_hChildStd_IN_Rd = null;
-            },
-        }
-        errdefer if (self.stdin_behavior == StdIo.Pipe) {
-            windowsDestroyPipe(g_hChildStd_IN_Rd, g_hChildStd_IN_Wr);
-        };
-
-        var g_hChildStd_OUT_Rd: ?windows.HANDLE = null;
-        var g_hChildStd_OUT_Wr: ?windows.HANDLE = null;
-        switch (self.stdout_behavior) {
-            StdIo.Pipe => {
-                try windowsMakeAsyncPipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr);
-            },
-            StdIo.Ignore => {
-                g_hChildStd_OUT_Wr = nul_handle;
-            },
-            StdIo.Inherit => {
-                g_hChildStd_OUT_Wr = windows.GetStdHandle(windows.STD_OUTPUT_HANDLE) catch null;
-            },
-            StdIo.Close => {
-                g_hChildStd_OUT_Wr = null;
-            },
-        }
-        errdefer if (self.stdout_behavior == StdIo.Pipe) {
-            windowsDestroyPipe(g_hChildStd_OUT_Rd, g_hChildStd_OUT_Wr);
-        };
-
-        var g_hChildStd_ERR_Rd: ?windows.HANDLE = null;
-        var g_hChildStd_ERR_Wr: ?windows.HANDLE = null;
-        switch (self.stderr_behavior) {
-            StdIo.Pipe => {
-                try windowsMakeAsyncPipe(&g_hChildStd_ERR_Rd, &g_hChildStd_ERR_Wr, &saAttr);
-            },
-            StdIo.Ignore => {
-                g_hChildStd_ERR_Wr = nul_handle;
-            },
-            StdIo.Inherit => {
-                g_hChildStd_ERR_Wr = windows.GetStdHandle(windows.STD_ERROR_HANDLE) catch null;
-            },
-            StdIo.Close => {
-                g_hChildStd_ERR_Wr = null;
-            },
-        }
-        errdefer if (self.stderr_behavior == StdIo.Pipe) {
-            windowsDestroyPipe(g_hChildStd_ERR_Rd, g_hChildStd_ERR_Wr);
-        };
-
-        var siStartInfo = windows.STARTUPINFOW{
-            .cb = @sizeOf(windows.STARTUPINFOW),
-            .hStdError = g_hChildStd_ERR_Wr,
-            .hStdOutput = g_hChildStd_OUT_Wr,
-            .hStdInput = g_hChildStd_IN_Rd,
-            .dwFlags = windows.STARTF_USESTDHANDLES,
-
-            .lpReserved = null,
-            .lpDesktop = null,
-            .lpTitle = null,
-            .dwX = 0,
-            .dwY = 0,
-            .dwXSize = 0,
-            .dwYSize = 0,
-            .dwXCountChars = 0,
-            .dwYCountChars = 0,
-            .dwFillAttribute = 0,
-            .wShowWindow = 0,
-            .cbReserved2 = 0,
-            .lpReserved2 = null,
-        };
-        var piProcInfo: windows.PROCESS_INFORMATION = undefined;
-
-        const cwd_w = if (self.cwd) |cwd| try unicode.wtf8ToWtf16LeAllocZ(self.allocator, cwd) else null;
-        defer if (cwd_w) |cwd| self.allocator.free(cwd);
-        const cwd_w_ptr = if (cwd_w) |cwd| cwd.ptr else null;
-
-        const maybe_envp_buf = if (self.env_map) |env_map| try createWindowsEnvBlock(self.allocator, env_map) else null;
-        defer if (maybe_envp_buf) |envp_buf| self.allocator.free(envp_buf);
-        const envp_ptr = if (maybe_envp_buf) |envp_buf| envp_buf.ptr else null;
-
-        const app_name_wtf8 = self.argv[0];
-        const app_name_is_absolute = fs.path.isAbsolute(app_name_wtf8);
-
-        // the cwd set in ChildProcess is in effect when choosing the executable path
-        // to match posix semantics
-        var cwd_path_w_needs_free = false;
-        const cwd_path_w = x: {
-            // If the app name is absolute, then we need to use its dirname as the cwd
-            if (app_name_is_absolute) {
-                cwd_path_w_needs_free = true;
-                const dir = fs.path.dirname(app_name_wtf8).?;
-                break :x try unicode.wtf8ToWtf16LeAllocZ(self.allocator, dir);
-            } else if (self.cwd) |cwd| {
-                cwd_path_w_needs_free = true;
-                break :x try unicode.wtf8ToWtf16LeAllocZ(self.allocator, cwd);
-            } else {
-                break :x &[_:0]u16{}; // empty for cwd
-            }
-        };
-        defer if (cwd_path_w_needs_free) self.allocator.free(cwd_path_w);
-
-        // If the app name has more than just a filename, then we need to separate that
-        // into the basename and dirname and use the dirname as an addition to the cwd
-        // path. This is because NtQueryDirectoryFile cannot accept FileName params with
-        // path separators.
-        const app_basename_wtf8 = fs.path.basename(app_name_wtf8);
-        // If the app name is absolute, then the cwd will already have the app's dirname in it,
-        // so only populate app_dirname if app name is a relative path with > 0 path separators.
-        const maybe_app_dirname_wtf8 = if (!app_name_is_absolute) fs.path.dirname(app_name_wtf8) else null;
-        const app_dirname_w: ?[:0]u16 = x: {
-            if (maybe_app_dirname_wtf8) |app_dirname_wtf8| {
-                break :x try unicode.wtf8ToWtf16LeAllocZ(self.allocator, app_dirname_wtf8);
-            }
-            break :x null;
-        };
-        defer if (app_dirname_w != null) self.allocator.free(app_dirname_w.?);
-
-        const app_name_w = try unicode.wtf8ToWtf16LeAllocZ(self.allocator, app_basename_wtf8);
-        defer self.allocator.free(app_name_w);
-
-        run: {
-            const PATH: [:0]const u16 = std.process.getenvW(unicode.utf8ToUtf16LeStringLiteral("PATH")) orelse &[_:0]u16{};
-            const PATHEXT: [:0]const u16 = std.process.getenvW(unicode.utf8ToUtf16LeStringLiteral("PATHEXT")) orelse &[_:0]u16{};
-
-            // In case the command ends up being a .bat/.cmd script, we need to escape things using the cmd.exe rules
-            // and invoke cmd.exe ourselves in order to mitigate arbitrary command execution from maliciously
-            // constructed arguments.
-            //
-            // We'll need to wait until we're actually trying to run the command to know for sure
-            // if the resolved command has the `.bat` or `.cmd` extension, so we defer actually
-            // serializing the command line until we determine how it should be serialized.
-            var cmd_line_cache = WindowsCommandLineCache.init(self.allocator, self.argv);
-            defer cmd_line_cache.deinit();
-
-            var app_buf = std.ArrayListUnmanaged(u16){};
-            defer app_buf.deinit(self.allocator);
-
-            try app_buf.appendSlice(self.allocator, app_name_w);
-
-            var dir_buf = std.ArrayListUnmanaged(u16){};
-            defer dir_buf.deinit(self.allocator);
-
-            if (cwd_path_w.len > 0) {
-                try dir_buf.appendSlice(self.allocator, cwd_path_w);
-            }
-            if (app_dirname_w) |app_dir| {
-                if (dir_buf.items.len > 0) try dir_buf.append(self.allocator, fs.path.sep);
-                try dir_buf.appendSlice(self.allocator, app_dir);
-            }
-            if (dir_buf.items.len > 0) {
-                // Need to normalize the path, openDirW can't handle things like double backslashes
-                const normalized_len = windows.normalizePath(u16, dir_buf.items) catch return error.BadPathName;
-                dir_buf.shrinkRetainingCapacity(normalized_len);
-            }
-
-            windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, &cmd_line_cache, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo) catch |no_path_err| {
-                const original_err = switch (no_path_err) {
-                    // argv[0] contains unsupported characters that will never resolve to a valid exe.
-                    error.InvalidArg0 => return error.FileNotFound,
-                    error.FileNotFound, error.InvalidExe, error.AccessDenied => |e| e,
-                    error.UnrecoverableInvalidExe => return error.InvalidExe,
-                    else => |e| return e,
-                };
-
-                // If the app name had path separators, that disallows PATH searching,
-                // and there's no need to search the PATH if the app name is absolute.
-                // We still search the path if the cwd is absolute because of the
-                // "cwd set in ChildProcess is in effect when choosing the executable path
-                // to match posix semantics" behavior--we don't want to skip searching
-                // the PATH just because we were trying to set the cwd of the child process.
-                if (app_dirname_w != null or app_name_is_absolute) {
-                    return original_err;
-                }
-
-                var it = mem.tokenizeScalar(u16, PATH, ';');
-                while (it.next()) |search_path| {
-                    dir_buf.clearRetainingCapacity();
-                    try dir_buf.appendSlice(self.allocator, search_path);
-                    // Need to normalize the path, some PATH values can contain things like double
-                    // backslashes which openDirW can't handle
-                    const normalized_len = windows.normalizePath(u16, dir_buf.items) catch continue;
-                    dir_buf.shrinkRetainingCapacity(normalized_len);
-
-                    if (windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, &cmd_line_cache, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo)) {
-                        break :run;
-                    } else |err| switch (err) {
-                        // argv[0] contains unsupported characters that will never resolve to a valid exe.
-                        error.InvalidArg0 => return error.FileNotFound,
-                        error.FileNotFound, error.AccessDenied, error.InvalidExe => continue,
-                        error.UnrecoverableInvalidExe => return error.InvalidExe,
-                        else => |e| return e,
-                    }
-                } else {
-                    return original_err;
-                }
-            };
-        }
-
-        if (g_hChildStd_IN_Wr) |h| {
-            self.stdin = File{ .handle = h };
-        } else {
-            self.stdin = null;
-        }
-        if (g_hChildStd_OUT_Rd) |h| {
-            self.stdout = File{ .handle = h };
-        } else {
-            self.stdout = null;
-        }
-        if (g_hChildStd_ERR_Rd) |h| {
-            self.stderr = File{ .handle = h };
-        } else {
-            self.stderr = null;
-        }
-
-        self.id = piProcInfo.hProcess;
-        self.thread_handle = piProcInfo.hThread;
-        self.term = null;
-
-        if (self.stdin_behavior == StdIo.Pipe) {
-            posix.close(g_hChildStd_IN_Rd.?);
-        }
-        if (self.stderr_behavior == StdIo.Pipe) {
-            posix.close(g_hChildStd_ERR_Wr.?);
-        }
-        if (self.stdout_behavior == StdIo.Pipe) {
-            posix.close(g_hChildStd_OUT_Wr.?);
-        }
-    }
-
-    fn setUpChildIo(stdio: StdIo, pipe_fd: i32, std_fileno: i32, dev_null_fd: i32) !void {
-        switch (stdio) {
-            .Pipe => try posix.dup2(pipe_fd, std_fileno),
-            .Close => posix.close(std_fileno),
-            .Inherit => {},
-            .Ignore => try posix.dup2(dev_null_fd, std_fileno),
-        }
-    }
-};
-
-/// Expects `app_buf` to contain exactly the app name, and `dir_buf` to contain exactly the dir path.
-/// After return, `app_buf` will always contain exactly the app name and `dir_buf` will always contain exactly the dir path.
-/// Note: `app_buf` should not contain any leading path separators.
-/// Note: If the dir is the cwd, dir_buf should be empty (len = 0).
-fn windowsCreateProcessPathExt(
-    allocator: mem.Allocator,
-    dir_buf: *std.ArrayListUnmanaged(u16),
-    app_buf: *std.ArrayListUnmanaged(u16),
-    pathext: [:0]const u16,
-    cmd_line_cache: *WindowsCommandLineCache,
-    envp_ptr: ?[*]u16,
-    cwd_ptr: ?[*:0]u16,
-    lpStartupInfo: *windows.STARTUPINFOW,
-    lpProcessInformation: *windows.PROCESS_INFORMATION,
-) !void {
-    const app_name_len = app_buf.items.len;
-    const dir_path_len = dir_buf.items.len;
-
-    if (app_name_len == 0) return error.FileNotFound;
-
-    defer app_buf.shrinkRetainingCapacity(app_name_len);
-    defer dir_buf.shrinkRetainingCapacity(dir_path_len);
-
-    // The name of the game here is to avoid CreateProcessW calls at all costs,
-    // and only ever try calling it when we have a real candidate for execution.
-    // Secondarily, we want to minimize the number of syscalls used when checking
-    // for each PATHEXT-appended version of the app name.
-    //
-    // An overview of the technique used:
-    // - Open the search directory for iteration (either cwd or a path from PATH)
-    // - Use NtQueryDirectoryFile with a wildcard filename of `<app name>*` to
-    //   check if anything that could possibly match either the unappended version
-    //   of the app name or any of the versions with a PATHEXT value appended exists.
-    // - If the wildcard NtQueryDirectoryFile call found nothing, we can exit early
-    //   without needing to use PATHEXT at all.
-    //
-    // This allows us to use a <open dir, NtQueryDirectoryFile, close dir> sequence
-    // for any directory that doesn't contain any possible matches, instead of having
-    // to use a separate look up for each individual filename combination (unappended +
-    // each PATHEXT appended). For directories where the wildcard *does* match something,
-    // we iterate the matches and take note of any that are either the unappended version,
-    // or a version with a supported PATHEXT appended. We then try calling CreateProcessW
-    // with the found versions in the appropriate order.
-
-    var dir = dir: {
-        // needs to be null-terminated
-        try dir_buf.append(allocator, 0);
-        defer dir_buf.shrinkRetainingCapacity(dir_path_len);
-        const dir_path_z = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
-        const prefixed_path = try windows.wToPrefixedFileW(null, dir_path_z);
-        break :dir fs.cwd().openDirW(prefixed_path.span().ptr, .{ .iterate = true }) catch
-            return error.FileNotFound;
-    };
-    defer dir.close();
-
-    // Add wildcard and null-terminator
-    try app_buf.append(allocator, '*');
-    try app_buf.append(allocator, 0);
-    const app_name_wildcard = app_buf.items[0 .. app_buf.items.len - 1 :0];
-
-    // This 2048 is arbitrary, we just want it to be large enough to get multiple FILE_DIRECTORY_INFORMATION entries
-    // returned per NtQueryDirectoryFile call.
-    var file_information_buf: [2048]u8 align(@alignOf(windows.FILE_DIRECTORY_INFORMATION)) = undefined;
-    const file_info_maximum_single_entry_size = @sizeOf(windows.FILE_DIRECTORY_INFORMATION) + (windows.NAME_MAX * 2);
-    if (file_information_buf.len < file_info_maximum_single_entry_size) {
-        @compileError("file_information_buf must be large enough to contain at least one maximum size FILE_DIRECTORY_INFORMATION entry");
-    }
-    var io_status: windows.IO_STATUS_BLOCK = undefined;
-
-    const num_supported_pathext = @typeInfo(CreateProcessSupportedExtension).Enum.fields.len;
-    var pathext_seen = [_]bool{false} ** num_supported_pathext;
-    var any_pathext_seen = false;
-    var unappended_exists = false;
-
-    // Fully iterate the wildcard matches via NtQueryDirectoryFile and take note of all versions
-    // of the app_name we should try to spawn.
-    // Note: This is necessary because the order of the files returned is filesystem-dependent:
-    //       On NTFS, `blah.exe*` will always return `blah.exe` first if it exists.
-    //       On FAT32, it's possible for something like `blah.exe.obj` to be returned first.
-    while (true) {
-        const app_name_len_bytes = math.cast(u16, app_name_wildcard.len * 2) orelse return error.NameTooLong;
-        var app_name_unicode_string = windows.UNICODE_STRING{
-            .Length = app_name_len_bytes,
-            .MaximumLength = app_name_len_bytes,
-            .Buffer = @constCast(app_name_wildcard.ptr),
-        };
-        const rc = windows.ntdll.NtQueryDirectoryFile(
-            dir.fd,
-            null,
-            null,
-            null,
-            &io_status,
-            &file_information_buf,
-            file_information_buf.len,
-            .FileDirectoryInformation,
-            windows.FALSE, // single result
-            &app_name_unicode_string,
-            windows.FALSE, // restart iteration
-        );
-
-        // If we get nothing with the wildcard, then we can just bail out
-        // as we know appending PATHEXT will not yield anything.
-        switch (rc) {
-            .SUCCESS => {},
-            .NO_SUCH_FILE => return error.FileNotFound,
-            .NO_MORE_FILES => break,
-            .ACCESS_DENIED => return error.AccessDenied,
-            else => return windows.unexpectedStatus(rc),
-        }
-
-        // According to the docs, this can only happen if there is not enough room in the
-        // buffer to write at least one complete FILE_DIRECTORY_INFORMATION entry.
-        // Therefore, this condition should not be possible to hit with the buffer size we use.
-        std.debug.assert(io_status.Information != 0);
-
-        var it = windows.FileInformationIterator(windows.FILE_DIRECTORY_INFORMATION){ .buf = &file_information_buf };
-        while (it.next()) |info| {
-            // Skip directories
-            if (info.FileAttributes & windows.FILE_ATTRIBUTE_DIRECTORY != 0) continue;
-            const filename = @as([*]u16, @ptrCast(&info.FileName))[0 .. info.FileNameLength / 2];
-            // Because all results start with the app_name since we're using the wildcard `app_name*`,
-            // if the length is equal to app_name then this is an exact match
-            if (filename.len == app_name_len) {
-                // Note: We can't break early here because it's possible that the unappended version
-                //       fails to spawn, in which case we still want to try the PATHEXT appended versions.
-                unappended_exists = true;
-            } else if (windowsCreateProcessSupportsExtension(filename[app_name_len..])) |pathext_ext| {
-                pathext_seen[@intFromEnum(pathext_ext)] = true;
-                any_pathext_seen = true;
-            }
-        }
-    }
-
-    const unappended_err = unappended: {
-        if (unappended_exists) {
-            if (dir_path_len != 0) switch (dir_buf.items[dir_buf.items.len - 1]) {
-                '/', '\\' => {},
-                else => try dir_buf.append(allocator, fs.path.sep),
-            };
-            try dir_buf.appendSlice(allocator, app_buf.items[0..app_name_len]);
-            try dir_buf.append(allocator, 0);
-            const full_app_name = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
-
-            const is_bat_or_cmd = bat_or_cmd: {
-                const app_name = app_buf.items[0..app_name_len];
-                const ext_start = std.mem.lastIndexOfScalar(u16, app_name, '.') orelse break :bat_or_cmd false;
-                const ext = app_name[ext_start..];
-                const ext_enum = windowsCreateProcessSupportsExtension(ext) orelse break :bat_or_cmd false;
-                switch (ext_enum) {
-                    .cmd, .bat => break :bat_or_cmd true,
-                    else => break :bat_or_cmd false,
-                }
-            };
-            const cmd_line_w = if (is_bat_or_cmd)
-                try cmd_line_cache.scriptCommandLine(full_app_name)
-            else
-                try cmd_line_cache.commandLine();
-            const app_name_w = if (is_bat_or_cmd)
-                try cmd_line_cache.cmdExePath()
-            else
-                full_app_name;
-
-            if (windowsCreateProcess(app_name_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
-                return;
-            } else |err| switch (err) {
-                error.FileNotFound,
-                error.AccessDenied,
-                => break :unappended err,
-                error.InvalidExe => {
-                    // On InvalidExe, if the extension of the app name is .exe then
-                    // it's treated as an unrecoverable error. Otherwise, it'll be
-                    // skipped as normal.
-                    const app_name = app_buf.items[0..app_name_len];
-                    const ext_start = std.mem.lastIndexOfScalar(u16, app_name, '.') orelse break :unappended err;
-                    const ext = app_name[ext_start..];
-                    if (windows.eqlIgnoreCaseWTF16(ext, unicode.utf8ToUtf16LeStringLiteral(".EXE"))) {
-                        return error.UnrecoverableInvalidExe;
-                    }
-                    break :unappended err;
-                },
-                else => return err,
-            }
-        }
-        break :unappended error.FileNotFound;
-    };
-
-    if (!any_pathext_seen) return unappended_err;
-
-    // Now try any PATHEXT appended versions that we've seen
-    var ext_it = mem.tokenizeScalar(u16, pathext, ';');
-    while (ext_it.next()) |ext| {
-        const ext_enum = windowsCreateProcessSupportsExtension(ext) orelse continue;
-        if (!pathext_seen[@intFromEnum(ext_enum)]) continue;
-
-        dir_buf.shrinkRetainingCapacity(dir_path_len);
-        if (dir_path_len != 0) switch (dir_buf.items[dir_buf.items.len - 1]) {
-            '/', '\\' => {},
-            else => try dir_buf.append(allocator, fs.path.sep),
-        };
-        try dir_buf.appendSlice(allocator, app_buf.items[0..app_name_len]);
-        try dir_buf.appendSlice(allocator, ext);
-        try dir_buf.append(allocator, 0);
-        const full_app_name = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
-
-        const is_bat_or_cmd = switch (ext_enum) {
-            .cmd, .bat => true,
-            else => false,
-        };
-        const cmd_line_w = if (is_bat_or_cmd)
-            try cmd_line_cache.scriptCommandLine(full_app_name)
-        else
-            try cmd_line_cache.commandLine();
-        const app_name_w = if (is_bat_or_cmd)
-            try cmd_line_cache.cmdExePath()
-        else
-            full_app_name;
-
-        if (windowsCreateProcess(app_name_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
-            return;
-        } else |err| switch (err) {
-            error.FileNotFound => continue,
-            error.AccessDenied => continue,
-            error.InvalidExe => {
-                // On InvalidExe, if the extension of the app name is .exe then
-                // it's treated as an unrecoverable error. Otherwise, it'll be
-                // skipped as normal.
-                if (windows.eqlIgnoreCaseWTF16(ext, unicode.utf8ToUtf16LeStringLiteral(".EXE"))) {
-                    return error.UnrecoverableInvalidExe;
-                }
-                continue;
-            },
-            else => return err,
-        }
-    }
-
-    return unappended_err;
-}
-
-fn windowsCreateProcess(app_name: [*:0]u16, cmd_line: [*:0]u16, envp_ptr: ?[*]u16, cwd_ptr: ?[*:0]u16, lpStartupInfo: *windows.STARTUPINFOW, lpProcessInformation: *windows.PROCESS_INFORMATION) !void {
-    // TODO the docs for environment pointer say:
-    // > A pointer to the environment block for the new process. If this parameter
-    // > is NULL, the new process uses the environment of the calling process.
-    // > ...
-    // > An environment block can contain either Unicode or ANSI characters. If
-    // > the environment block pointed to by lpEnvironment contains Unicode
-    // > characters, be sure that dwCreationFlags includes CREATE_UNICODE_ENVIRONMENT.
-    // > If this parameter is NULL and the environment block of the parent process
-    // > contains Unicode characters, you must also ensure that dwCreationFlags
-    // > includes CREATE_UNICODE_ENVIRONMENT.
-    // This seems to imply that we have to somehow know whether our process parent passed
-    // CREATE_UNICODE_ENVIRONMENT if we want to pass NULL for the environment parameter.
-    // Since we do not know this information that would imply that we must not pass NULL
-    // for the parameter.
-    // However this would imply that programs compiled with -DUNICODE could not pass
-    // environment variables to programs that were not, which seems unlikely.
-    // More investigation is needed.
-    return windows.CreateProcessW(
-        app_name,
-        cmd_line,
-        null,
-        null,
-        windows.TRUE,
-        windows.CREATE_UNICODE_ENVIRONMENT,
-        @as(?*anyopaque, @ptrCast(envp_ptr)),
-        cwd_ptr,
-        lpStartupInfo,
-        lpProcessInformation,
-    );
-}
-
-// Should be kept in sync with `windowsCreateProcessSupportsExtension`
-const CreateProcessSupportedExtension = enum {
-    bat,
-    cmd,
-    com,
-    exe,
-};
-
-/// Case-insensitive WTF-16 lookup
-fn windowsCreateProcessSupportsExtension(ext: []const u16) ?CreateProcessSupportedExtension {
-    if (ext.len != 4) return null;
-    const State = enum {
-        start,
-        dot,
-        b,
-        ba,
-        c,
-        cm,
-        co,
-        e,
-        ex,
-    };
-    var state: State = .start;
-    for (ext) |c| switch (state) {
-        .start => switch (c) {
-            '.' => state = .dot,
-            else => return null,
-        },
-        .dot => switch (c) {
-            'b', 'B' => state = .b,
-            'c', 'C' => state = .c,
-            'e', 'E' => state = .e,
-            else => return null,
-        },
-        .b => switch (c) {
-            'a', 'A' => state = .ba,
-            else => return null,
-        },
-        .c => switch (c) {
-            'm', 'M' => state = .cm,
-            'o', 'O' => state = .co,
-            else => return null,
-        },
-        .e => switch (c) {
-            'x', 'X' => state = .ex,
-            else => return null,
-        },
-        .ba => switch (c) {
-            't', 'T' => return .bat,
-            else => return null,
-        },
-        .cm => switch (c) {
-            'd', 'D' => return .cmd,
-            else => return null,
-        },
-        .co => switch (c) {
-            'm', 'M' => return .com,
-            else => return null,
-        },
-        .ex => switch (c) {
-            'e', 'E' => return .exe,
-            else => return null,
-        },
-    };
-    return null;
-}
-
-test windowsCreateProcessSupportsExtension {
-    try std.testing.expectEqual(CreateProcessSupportedExtension.exe, windowsCreateProcessSupportsExtension(&[_]u16{ '.', 'e', 'X', 'e' }).?);
-    try std.testing.expect(windowsCreateProcessSupportsExtension(&[_]u16{ '.', 'e', 'X', 'e', 'c' }) == null);
-}
-
-/// Serializes argv into a WTF-16 encoded command-line string for use with CreateProcessW.
-///
-/// Serialization is done on-demand and the result is cached in order to allow for:
-/// - Only serializing the particular type of command line needed (`.bat`/`.cmd`
-///   command line serialization is different from `.exe`/etc)
-/// - Reusing the serialized command lines if necessary (i.e. if the execution
-///   of a command fails and the PATH is going to be continued to be searched
-///   for more candidates)
-pub const WindowsCommandLineCache = struct {
-    cmd_line: ?[:0]u16 = null,
-    script_cmd_line: ?[:0]u16 = null,
-    cmd_exe_path: ?[:0]u16 = null,
-    argv: []const []const u8,
-    allocator: mem.Allocator,
-
-    pub fn init(allocator: mem.Allocator, argv: []const []const u8) WindowsCommandLineCache {
-        return .{
-            .allocator = allocator,
-            .argv = argv,
-        };
-    }
-
-    pub fn deinit(self: *WindowsCommandLineCache) void {
-        if (self.cmd_line) |cmd_line| self.allocator.free(cmd_line);
-        if (self.script_cmd_line) |script_cmd_line| self.allocator.free(script_cmd_line);
-        if (self.cmd_exe_path) |cmd_exe_path| self.allocator.free(cmd_exe_path);
-    }
-
-    pub fn commandLine(self: *WindowsCommandLineCache) ![:0]u16 {
-        if (self.cmd_line == null) {
-            self.cmd_line = try argvToCommandLineWindows(self.allocator, self.argv);
-        }
-        return self.cmd_line.?;
-    }
-
-    /// Not cached, since the path to the batch script will change during PATH searching.
-    /// `script_path` should be as qualified as possible, e.g. if the PATH is being searched,
-    /// then script_path should include both the search path and the script filename
-    /// (this allows avoiding cmd.exe having to search the PATH again).
-    pub fn scriptCommandLine(self: *WindowsCommandLineCache, script_path: []const u16) ![:0]u16 {
-        if (self.script_cmd_line) |v| self.allocator.free(v);
-        self.script_cmd_line = try argvToScriptCommandLineWindows(
-            self.allocator,
-            script_path,
-            self.argv[1..],
-        );
-        return self.script_cmd_line.?;
-    }
-
-    pub fn cmdExePath(self: *WindowsCommandLineCache) ![:0]u16 {
-        if (self.cmd_exe_path == null) {
-            self.cmd_exe_path = try windowsCmdExePath(self.allocator);
-        }
-        return self.cmd_exe_path.?;
-    }
-};
-
-pub fn windowsCmdExePath(allocator: mem.Allocator) error{ OutOfMemory, Unexpected }![:0]u16 {
-    var buf = try std.ArrayListUnmanaged(u16).initCapacity(allocator, 128);
-    errdefer buf.deinit(allocator);
-    while (true) {
-        const unused_slice = buf.unusedCapacitySlice();
-        // TODO: Get the system directory from PEB.ReadOnlyStaticServerData
-        const len = windows.kernel32.GetSystemDirectoryW(@ptrCast(unused_slice), @intCast(unused_slice.len));
-        if (len == 0) {
-            switch (windows.kernel32.GetLastError()) {
-                else => |err| return windows.unexpectedError(err),
-            }
-        }
-        if (len > unused_slice.len) {
-            try buf.ensureUnusedCapacity(allocator, len);
-        } else {
-            buf.items.len = len;
-            break;
-        }
-    }
-    switch (buf.items[buf.items.len - 1]) {
-        '/', '\\' => {},
-        else => try buf.append(allocator, fs.path.sep),
-    }
-    try buf.appendSlice(allocator, std.unicode.utf8ToUtf16LeStringLiteral("cmd.exe"));
-    return try buf.toOwnedSliceSentinel(allocator, 0);
-}
-
-pub const ArgvToScriptCommandLineError = error{
-    OutOfMemory,
-    InvalidWtf8,
-    /// NUL (U+0000), LF (U+000A), CR (U+000D) are not allowed
-    /// within arguments when executing a `.bat`/`.cmd` script.
-    /// - NUL/LF signifiies end of arguments, so anything afterwards
-    ///   would be lost after execution.
-    /// - CR is stripped by `cmd.exe`, so any CR codepoints
-    ///   would be lost after execution.
-    InvalidBatchScriptArg,
-};
-
-/// Serializes `argv` to a Windows command-line string that uses `cmd.exe /c` and `cmd.exe`-specific
-/// escaping rules. The caller owns the returned slice.
-///
-/// Escapes `argv` using the suggested mitigation against arbitrary command execution from:
-/// https://flatt.tech/research/posts/batbadbut-you-cant-securely-execute-commands-on-windows/
-pub fn argvToScriptCommandLineWindows(
-    allocator: mem.Allocator,
-    /// Path to the `.bat`/`.cmd` script. If this path is relative, it is assumed to be relative to the CWD.
-    /// The script must have been verified to exist at this path before calling this function.
-    script_path: []const u16,
-    /// Arguments, not including the script name itself. Expected to be encoded as WTF-8.
-    script_args: []const []const u8,
-) ArgvToScriptCommandLineError![:0]u16 {
-    var buf = try std.ArrayList(u8).initCapacity(allocator, 64);
-    defer buf.deinit();
-
-    // `/d` disables execution of AutoRun commands.
-    // `/e:ON` and `/v:OFF` are needed for BatBadBut mitigation:
-    // > If delayed expansion is enabled via the registry value DelayedExpansion,
-    // > it must be disabled by explicitly calling cmd.exe with the /V:OFF option.
-    // > Escaping for % requires the command extension to be enabled.
-    // > If itโ€™s disabled via the registry value EnableExtensions, it must be enabled with the /E:ON option.
-    // https://flatt.tech/research/posts/batbadbut-you-cant-securely-execute-commands-on-windows/
-    buf.appendSliceAssumeCapacity("cmd.exe /d /e:ON /v:OFF /c \"");
-
-    // Always quote the path to the script arg
-    buf.appendAssumeCapacity('"');
-    // We always want the path to the batch script to include a path separator in order to
-    // avoid cmd.exe searching the PATH for the script. This is not part of the arbitrary
-    // command execution mitigation, we just know exactly what script we want to execute
-    // at this point, and potentially making cmd.exe re-find it is unnecessary.
-    //
-    // If the script path does not have a path separator, then we know its relative to CWD and
-    // we can just put `.\` in the front.
-    if (mem.indexOfAny(u16, script_path, &[_]u16{ mem.nativeToLittle(u16, '\\'), mem.nativeToLittle(u16, '/') }) == null) {
-        try buf.appendSlice(".\\");
-    }
-    // Note that we don't do any escaping/mitigations for this argument, since the relevant
-    // characters (", %, etc) are illegal in file paths and this function should only be called
-    // with script paths that have been verified to exist.
-    try std.unicode.wtf16LeToWtf8ArrayList(&buf, script_path);
-    buf.appendAssumeCapacity('"');
-
-    for (script_args) |arg| {
-        // Literal carriage returns get stripped when run through cmd.exe
-        // and NUL/newlines act as 'end of command.' Because of this, it's basically
-        // always a mistake to include these characters in argv, so it's
-        // an error condition in order to ensure that the return of this
-        // function can always roundtrip through cmd.exe.
-        if (std.mem.indexOfAny(u8, arg, "\x00\r\n") != null) {
-            return error.InvalidBatchScriptArg;
-        }
-
-        // Separate args with a space.
-        try buf.append(' ');
-
-        // Need to quote if the argument is empty (otherwise the arg would just be lost)
-        // or if the last character is a `\`, since then something like "%~2" in a .bat
-        // script would cause the closing " to be escaped which we don't want.
-        var needs_quotes = arg.len == 0 or arg[arg.len - 1] == '\\';
-        if (!needs_quotes) {
-            for (arg) |c| {
-                switch (c) {
-                    // Known good characters that don't need to be quoted
-                    'A'...'Z', 'a'...'z', '0'...'9', '#', '$', '*', '+', '-', '.', '/', ':', '?', '@', '\\', '_' => {},
-                    // When in doubt, quote
-                    else => {
-                        needs_quotes = true;
-                        break;
-                    },
-                }
-            }
-        }
-        if (needs_quotes) {
-            try buf.append('"');
-        }
-        var backslashes: usize = 0;
-        for (arg) |c| {
-            switch (c) {
-                '\\' => {
-                    backslashes += 1;
-                },
-                '"' => {
-                    try buf.appendNTimes('\\', backslashes);
-                    try buf.append('"');
-                    backslashes = 0;
-                },
-                // Replace `%` with `%%cd:~,%`.
-                //
-                // cmd.exe allows extracting a substring from an environment
-                // variable with the syntax: `%foo:~<start_index>,<end_index>%`.
-                // Therefore, `%cd:~,%` will always expand to an empty string
-                // since both the start and end index are blank, and it is assumed
-                // that `%cd%` is always available since it is a built-in variable
-                // that corresponds to the current directory.
-                //
-                // This means that replacing `%foo%` with `%%cd:~,%foo%%cd:~,%`
-                // will stop `%foo%` from being expanded and *after* expansion
-                // we'll still be left with `%foo%` (the literal string).
-                '%' => {
-                    // the trailing `%` is appended outside the switch
-                    try buf.appendSlice("%%cd:~,");
-                    backslashes = 0;
-                },
-                else => {
-                    backslashes = 0;
-                },
-            }
-            try buf.append(c);
-        }
-        if (needs_quotes) {
-            try buf.appendNTimes('\\', backslashes);
-            try buf.append('"');
-        }
-    }
-
-    try buf.append('"');
-
-    return try unicode.wtf8ToWtf16LeAllocZ(allocator, buf.items);
-}
-
-pub const ArgvToCommandLineError = error{ OutOfMemory, InvalidWtf8, InvalidArg0 };
-
-/// Serializes `argv` to a Windows command-line string suitable for passing to a child process and
-/// parsing by the `CommandLineToArgvW` algorithm. The caller owns the returned slice.
-pub fn argvToCommandLineWindows(
-    allocator: mem.Allocator,
-    argv: []const []const u8,
-) ArgvToCommandLineError![:0]u16 {
-    var buf = std.ArrayList(u8).init(allocator);
-    defer buf.deinit();
-
-    if (argv.len != 0) {
-        const arg0 = argv[0];
-
-        // The first argument must be quoted if it contains spaces or ASCII control characters
-        // (excluding DEL). It also follows special quoting rules where backslashes have no special
-        // interpretation, which makes it impossible to pass certain first arguments containing
-        // double quotes to a child process without characters from the first argument leaking into
-        // subsequent ones (which could have security implications).
-        //
-        // Empty arguments technically don't need quotes, but we quote them anyway for maximum
-        // compatibility with different implementations of the 'CommandLineToArgvW' algorithm.
-        //
-        // Double quotes are illegal in paths on Windows, so for the sake of simplicity we reject
-        // all first arguments containing double quotes, even ones that we could theoretically
-        // serialize in unquoted form.
-        var needs_quotes = arg0.len == 0;
-        for (arg0) |c| {
-            if (c <= ' ') {
-                needs_quotes = true;
-            } else if (c == '"') {
-                return error.InvalidArg0;
-            }
-        }
-        if (needs_quotes) {
-            try buf.append('"');
-            try buf.appendSlice(arg0);
-            try buf.append('"');
-        } else {
-            try buf.appendSlice(arg0);
-        }
-
-        for (argv[1..]) |arg| {
-            try buf.append(' ');
-
-            // Subsequent arguments must be quoted if they contain spaces, tabs or double quotes,
-            // or if they are empty. For simplicity and for maximum compatibility with different
-            // implementations of the 'CommandLineToArgvW' algorithm, we also quote all ASCII
-            // control characters (again, excluding DEL).
-            needs_quotes = for (arg) |c| {
-                if (c <= ' ' or c == '"') {
-                    break true;
-                }
-            } else arg.len == 0;
-            if (!needs_quotes) {
-                try buf.appendSlice(arg);
-                continue;
-            }
-
-            try buf.append('"');
-            var backslash_count: usize = 0;
-            for (arg) |byte| {
-                switch (byte) {
-                    '\\' => {
-                        backslash_count += 1;
-                    },
-                    '"' => {
-                        try buf.appendNTimes('\\', backslash_count * 2 + 1);
-                        try buf.append('"');
-                        backslash_count = 0;
-                    },
-                    else => {
-                        try buf.appendNTimes('\\', backslash_count);
-                        try buf.append(byte);
-                        backslash_count = 0;
-                    },
-                }
-            }
-            try buf.appendNTimes('\\', backslash_count * 2);
-            try buf.append('"');
-        }
-    }
-
-    return try unicode.wtf8ToWtf16LeAllocZ(allocator, buf.items);
-}
-
-test argvToCommandLineWindows {
-    const t = testArgvToCommandLineWindows;
-
-    try t(&.{
-        \\C:\Program Files\zig\zig.exe
-        ,
-        \\run
-        ,
-        \\.\src\main.zig
-        ,
-        \\-target
-        ,
-        \\x86_64-windows-gnu
-        ,
-        \\-O
-        ,
-        \\ReleaseSafe
-        ,
-        \\--
-        ,
-        \\--emoji=๐Ÿ—ฟ
-        ,
-        \\--eval=new Regex("Dwayne \"The Rock\" Johnson")
-        ,
-    },
-        \\"C:\Program Files\zig\zig.exe" run .\src\main.zig -target x86_64-windows-gnu -O ReleaseSafe -- --emoji=๐Ÿ—ฟ "--eval=new Regex(\"Dwayne \\\"The Rock\\\" Johnson\")"
-    );
-
-    try t(&.{}, "");
-    try t(&.{""}, "\"\"");
-    try t(&.{" "}, "\" \"");
-    try t(&.{"\t"}, "\"\t\"");
-    try t(&.{"\x07"}, "\"\x07\"");
-    try t(&.{"๐ŸฆŽ"}, "๐ŸฆŽ");
-
-    try t(
-        &.{ "zig", "aa aa", "bb\tbb", "cc\ncc", "dd\r\ndd", "ee\x7Fee" },
-        "zig \"aa aa\" \"bb\tbb\" \"cc\ncc\" \"dd\r\ndd\" ee\x7Fee",
-    );
-
-    try t(
-        &.{ "\\\\foo bar\\foo bar\\", "\\\\zig zag\\zig zag\\" },
-        "\"\\\\foo bar\\foo bar\\\" \"\\\\zig zag\\zig zag\\\\\"",
-    );
-
-    try std.testing.expectError(
-        error.InvalidArg0,
-        argvToCommandLineWindows(std.testing.allocator, &.{"\"quotes\"quotes\""}),
-    );
-    try std.testing.expectError(
-        error.InvalidArg0,
-        argvToCommandLineWindows(std.testing.allocator, &.{"quotes\"quotes"}),
-    );
-    try std.testing.expectError(
-        error.InvalidArg0,
-        argvToCommandLineWindows(std.testing.allocator, &.{"q u o t e s \" q u o t e s"}),
-    );
-}
-
-fn testArgvToCommandLineWindows(argv: []const []const u8, expected_cmd_line: []const u8) !void {
-    const cmd_line_w = try argvToCommandLineWindows(std.testing.allocator, argv);
-    defer std.testing.allocator.free(cmd_line_w);
-
-    const cmd_line = try unicode.wtf16LeToWtf8Alloc(std.testing.allocator, cmd_line_w);
-    defer std.testing.allocator.free(cmd_line);
-
-    try std.testing.expectEqualStrings(expected_cmd_line, cmd_line);
-}
-
-fn windowsDestroyPipe(rd: ?windows.HANDLE, wr: ?windows.HANDLE) void {
-    if (rd) |h| posix.close(h);
-    if (wr) |h| posix.close(h);
-}
-
-fn windowsMakePipeIn(rd: *?windows.HANDLE, wr: *?windows.HANDLE, sattr: *const windows.SECURITY_ATTRIBUTES) !void {
-    var rd_h: windows.HANDLE = undefined;
-    var wr_h: windows.HANDLE = undefined;
-    try windows.CreatePipe(&rd_h, &wr_h, sattr);
-    errdefer windowsDestroyPipe(rd_h, wr_h);
-    try windows.SetHandleInformation(wr_h, windows.HANDLE_FLAG_INHERIT, 0);
-    rd.* = rd_h;
-    wr.* = wr_h;
-}
-
-var pipe_name_counter = std.atomic.Value(u32).init(1);
-
-fn windowsMakeAsyncPipe(rd: *?windows.HANDLE, wr: *?windows.HANDLE, sattr: *const windows.SECURITY_ATTRIBUTES) !void {
-    var tmp_bufw: [128]u16 = undefined;
-
-    // Anonymous pipes are built upon Named pipes.
-    // https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-createpipe
-    // Asynchronous (overlapped) read and write operations are not supported by anonymous pipes.
-    // https://docs.microsoft.com/en-us/windows/win32/ipc/anonymous-pipe-operations
-    const pipe_path = blk: {
-        var tmp_buf: [128]u8 = undefined;
-        // Forge a random path for the pipe.
-        const pipe_path = std.fmt.bufPrintZ(
-            &tmp_buf,
-            "\\\\.\\pipe\\zig-childprocess-{d}-{d}",
-            .{ windows.GetCurrentProcessId(), pipe_name_counter.fetchAdd(1, .monotonic) },
-        ) catch unreachable;
-        const len = std.unicode.wtf8ToWtf16Le(&tmp_bufw, pipe_path) catch unreachable;
-        tmp_bufw[len] = 0;
-        break :blk tmp_bufw[0..len :0];
-    };
-
-    // Create the read handle that can be used with overlapped IO ops.
-    const read_handle = windows.kernel32.CreateNamedPipeW(
-        pipe_path.ptr,
-        windows.PIPE_ACCESS_INBOUND | windows.FILE_FLAG_OVERLAPPED,
-        windows.PIPE_TYPE_BYTE,
-        1,
-        4096,
-        4096,
-        0,
-        sattr,
-    );
-    if (read_handle == windows.INVALID_HANDLE_VALUE) {
-        switch (windows.kernel32.GetLastError()) {
-            else => |err| return windows.unexpectedError(err),
-        }
-    }
-    errdefer posix.close(read_handle);
-
-    var sattr_copy = sattr.*;
-    const write_handle = windows.kernel32.CreateFileW(
-        pipe_path.ptr,
-        windows.GENERIC_WRITE,
-        0,
-        &sattr_copy,
-        windows.OPEN_EXISTING,
-        windows.FILE_ATTRIBUTE_NORMAL,
-        null,
-    );
-    if (write_handle == windows.INVALID_HANDLE_VALUE) {
-        switch (windows.kernel32.GetLastError()) {
-            else => |err| return windows.unexpectedError(err),
-        }
-    }
-    errdefer posix.close(write_handle);
-
-    try windows.SetHandleInformation(read_handle, windows.HANDLE_FLAG_INHERIT, 0);
-
-    rd.* = read_handle;
-    wr.* = write_handle;
-}
-
-fn destroyPipe(pipe: [2]posix.fd_t) void {
-    posix.close(pipe[0]);
-    if (pipe[0] != pipe[1]) posix.close(pipe[1]);
-}
-
-// Child of fork calls this to report an error to the fork parent.
-// Then the child exits.
-fn forkChildErrReport(fd: i32, err: ChildProcess.SpawnError) noreturn {
-    writeIntFd(fd, @as(ErrInt, @intFromError(err))) catch {};
-    // If we're linking libc, some naughty applications may have registered atexit handlers
-    // which we really do not want to run in the fork child. I caught LLVM doing this and
-    // it caused a deadlock instead of doing an exit syscall. In the words of Avril Lavigne,
-    // "Why'd you have to go and make things so complicated?"
-    if (builtin.link_libc) {
-        // The _exit(2) function does nothing but make the exit syscall, unlike exit(3)
-        std.c._exit(1);
-    }
-    posix.exit(1);
-}
-
-const ErrInt = std.meta.Int(.unsigned, @sizeOf(anyerror) * 8);
-
-fn writeIntFd(fd: i32, value: ErrInt) !void {
-    const file = File{ .handle = fd };
-    file.writer().writeInt(u64, @intCast(value), .little) catch return error.SystemResources;
-}
-
-fn readIntFd(fd: i32) !ErrInt {
-    const file = File{ .handle = fd };
-    return @as(ErrInt, @intCast(file.reader().readInt(u64, .little) catch return error.SystemResources));
-}
-
-/// Caller must free result.
-pub fn createWindowsEnvBlock(allocator: mem.Allocator, env_map: *const EnvMap) ![]u16 {
-    // count bytes needed
-    const max_chars_needed = x: {
-        var max_chars_needed: usize = 4; // 4 for the final 4 null bytes
-        var it = env_map.iterator();
-        while (it.next()) |pair| {
-            // +1 for '='
-            // +1 for null byte
-            max_chars_needed += pair.key_ptr.len + pair.value_ptr.len + 2;
-        }
-        break :x max_chars_needed;
-    };
-    const result = try allocator.alloc(u16, max_chars_needed);
-    errdefer allocator.free(result);
-
-    var it = env_map.iterator();
-    var i: usize = 0;
-    while (it.next()) |pair| {
-        i += try unicode.wtf8ToWtf16Le(result[i..], pair.key_ptr.*);
-        result[i] = '=';
-        i += 1;
-        i += try unicode.wtf8ToWtf16Le(result[i..], pair.value_ptr.*);
-        result[i] = 0;
-        i += 1;
-    }
-    result[i] = 0;
-    i += 1;
-    result[i] = 0;
-    i += 1;
-    result[i] = 0;
-    i += 1;
-    result[i] = 0;
-    i += 1;
-    return try allocator.realloc(result, i);
-}
-
-pub fn createNullDelimitedEnvMap(arena: mem.Allocator, env_map: *const EnvMap) ![:null]?[*:0]u8 {
-    const envp_count = env_map.count();
-    const envp_buf = try arena.allocSentinel(?[*:0]u8, envp_count, null);
-    {
-        var it = env_map.iterator();
-        var i: usize = 0;
-        while (it.next()) |pair| : (i += 1) {
-            const env_buf = try arena.allocSentinel(u8, pair.key_ptr.len + pair.value_ptr.len + 1, 0);
-            @memcpy(env_buf[0..pair.key_ptr.len], pair.key_ptr.*);
-            env_buf[pair.key_ptr.len] = '=';
-            @memcpy(env_buf[pair.key_ptr.len + 1 ..][0..pair.value_ptr.len], pair.value_ptr.*);
-            envp_buf[i] = env_buf.ptr;
-        }
-        assert(i == envp_count);
-    }
-    return envp_buf;
-}
-
-test createNullDelimitedEnvMap {
-    const testing = std.testing;
-    const allocator = testing.allocator;
-    var envmap = EnvMap.init(allocator);
-    defer envmap.deinit();
-
-    try envmap.put("HOME", "/home/ifreund");
-    try envmap.put("WAYLAND_DISPLAY", "wayland-1");
-    try envmap.put("DISPLAY", ":1");
-    try envmap.put("DEBUGINFOD_URLS", " ");
-    try envmap.put("XCURSOR_SIZE", "24");
-
-    var arena = std.heap.ArenaAllocator.init(allocator);
-    defer arena.deinit();
-    const environ = try createNullDelimitedEnvMap(arena.allocator(), &envmap);
-
-    try testing.expectEqual(@as(usize, 5), environ.len);
-
-    inline for (.{
-        "HOME=/home/ifreund",
-        "WAYLAND_DISPLAY=wayland-1",
-        "DISPLAY=:1",
-        "DEBUGINFOD_URLS= ",
-        "XCURSOR_SIZE=24",
-    }) |target| {
-        for (environ) |variable| {
-            if (mem.eql(u8, mem.span(variable orelse continue), target)) break;
-        } else {
-            try testing.expect(false); // Environment variable not found
-        }
-    }
-}
lib/std/process.zig
@@ -6,12 +6,12 @@ const math = std.math;
 const Allocator = mem.Allocator;
 const assert = std.debug.assert;
 const testing = std.testing;
-const child_process = @import("child_process.zig");
 const native_os = builtin.os.tag;
 const posix = std.posix;
 const windows = std.os.windows;
+const unicode = std.unicode;
 
-pub const Child = child_process.ChildProcess;
+pub const Child = @import("process/Child.zig");
 pub const abort = posix.abort;
 pub const exit = posix.exit;
 pub const changeCurDir = posix.chdir;
@@ -86,7 +86,7 @@ pub const EnvMap = struct {
             _ = self;
             if (native_os == .windows) {
                 var h = std.hash.Wyhash.init(0);
-                var it = std.unicode.Wtf8View.initUnchecked(s).iterator();
+                var it = unicode.Wtf8View.initUnchecked(s).iterator();
                 while (it.nextCodepoint()) |cp| {
                     const cp_upper = upcase(cp);
                     h.update(&[_]u8{
@@ -103,8 +103,8 @@ pub const EnvMap = struct {
         pub fn eql(self: @This(), a: []const u8, b: []const u8) bool {
             _ = self;
             if (native_os == .windows) {
-                var it_a = std.unicode.Wtf8View.initUnchecked(a).iterator();
-                var it_b = std.unicode.Wtf8View.initUnchecked(b).iterator();
+                var it_a = unicode.Wtf8View.initUnchecked(a).iterator();
+                var it_b = unicode.Wtf8View.initUnchecked(b).iterator();
                 while (true) {
                     const c_a = it_a.nextCodepoint() orelse break;
                     const c_b = it_b.nextCodepoint() orelse return false;
@@ -141,7 +141,7 @@ pub const EnvMap = struct {
     /// If `putMove` fails, the ownership of key and value does not transfer.
     /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
     pub fn putMove(self: *EnvMap, key: []u8, value: []u8) !void {
-        assert(std.unicode.wtf8ValidateSlice(key));
+        assert(unicode.wtf8ValidateSlice(key));
         const get_or_put = try self.hash_map.getOrPut(key);
         if (get_or_put.found_existing) {
             self.free(get_or_put.key_ptr.*);
@@ -154,7 +154,7 @@ pub const EnvMap = struct {
     /// `key` and `value` are copied into the EnvMap.
     /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
     pub fn put(self: *EnvMap, key: []const u8, value: []const u8) !void {
-        assert(std.unicode.wtf8ValidateSlice(key));
+        assert(unicode.wtf8ValidateSlice(key));
         const value_copy = try self.copy(value);
         errdefer self.free(value_copy);
         const get_or_put = try self.hash_map.getOrPut(key);
@@ -173,7 +173,7 @@ pub const EnvMap = struct {
     /// The returned pointer is invalidated if the map resizes.
     /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
     pub fn getPtr(self: EnvMap, key: []const u8) ?*[]const u8 {
-        assert(std.unicode.wtf8ValidateSlice(key));
+        assert(unicode.wtf8ValidateSlice(key));
         return self.hash_map.getPtr(key);
     }
 
@@ -182,7 +182,7 @@ pub const EnvMap = struct {
     /// key is removed from the map.
     /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
     pub fn get(self: EnvMap, key: []const u8) ?[]const u8 {
-        assert(std.unicode.wtf8ValidateSlice(key));
+        assert(unicode.wtf8ValidateSlice(key));
         return self.hash_map.get(key);
     }
 
@@ -190,7 +190,7 @@ pub const EnvMap = struct {
     /// This invalidates the value returned by get() for this key.
     /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
     pub fn remove(self: *EnvMap, key: []const u8) void {
-        assert(std.unicode.wtf8ValidateSlice(key));
+        assert(unicode.wtf8ValidateSlice(key));
         const kv = self.hash_map.fetchRemove(key) orelse return;
         self.free(kv.key);
         self.free(kv.value);
@@ -260,7 +260,7 @@ test EnvMap {
         try testing.expectEqualStrings("something else", env.get("ะบะธั€ะธะปะปะธั†ะฐ").?);
 
         // and WTF-8 that's not valid UTF-8
-        const wtf8_with_surrogate_pair = try std.unicode.wtf16LeToWtf8Alloc(testing.allocator, &[_]u16{
+        const wtf8_with_surrogate_pair = try unicode.wtf16LeToWtf8Alloc(testing.allocator, &[_]u16{
             std.mem.nativeToLittle(u16, 0xD83D), // unpaired high surrogate
         });
         defer testing.allocator.free(wtf8_with_surrogate_pair);
@@ -300,7 +300,7 @@ pub fn getEnvMap(allocator: Allocator) GetEnvMapError!EnvMap {
 
             while (ptr[i] != 0 and ptr[i] != '=') : (i += 1) {}
             const key_w = ptr[key_start..i];
-            const key = try std.unicode.wtf16LeToWtf8Alloc(allocator, key_w);
+            const key = try unicode.wtf16LeToWtf8Alloc(allocator, key_w);
             errdefer allocator.free(key);
 
             if (ptr[i] == '=') i += 1;
@@ -308,7 +308,7 @@ pub fn getEnvMap(allocator: Allocator) GetEnvMapError!EnvMap {
             const value_start = i;
             while (ptr[i] != 0) : (i += 1) {}
             const value_w = ptr[value_start..i];
-            const value = try std.unicode.wtf16LeToWtf8Alloc(allocator, value_w);
+            const value = try unicode.wtf16LeToWtf8Alloc(allocator, value_w);
             errdefer allocator.free(value);
 
             i += 1; // skip over null byte
@@ -401,13 +401,13 @@ pub fn getEnvVarOwned(allocator: Allocator, key: []const u8) GetEnvVarOwnedError
         const result_w = blk: {
             var stack_alloc = std.heap.stackFallback(256 * @sizeOf(u16), allocator);
             const stack_allocator = stack_alloc.get();
-            const key_w = try std.unicode.wtf8ToWtf16LeAllocZ(stack_allocator, key);
+            const key_w = try unicode.wtf8ToWtf16LeAllocZ(stack_allocator, key);
             defer stack_allocator.free(key_w);
 
             break :blk getenvW(key_w) orelse return error.EnvironmentVariableNotFound;
         };
         // wtf16LeToWtf8Alloc can only fail with OutOfMemory
-        return std.unicode.wtf16LeToWtf8Alloc(allocator, result_w);
+        return unicode.wtf16LeToWtf8Alloc(allocator, result_w);
     } else if (native_os == .wasi and !builtin.link_libc) {
         var envmap = getEnvMap(allocator) catch return error.OutOfMemory;
         defer envmap.deinit();
@@ -422,7 +422,7 @@ pub fn getEnvVarOwned(allocator: Allocator, key: []const u8) GetEnvVarOwnedError
 /// On Windows, `key` must be valid UTF-8.
 pub fn hasEnvVarConstant(comptime key: []const u8) bool {
     if (native_os == .windows) {
-        const key_w = comptime std.unicode.utf8ToUtf16LeStringLiteral(key);
+        const key_w = comptime unicode.utf8ToUtf16LeStringLiteral(key);
         return getenvW(key_w) != null;
     } else if (native_os == .wasi and !builtin.link_libc) {
         @compileError("hasEnvVarConstant is not supported for WASI without libc");
@@ -445,7 +445,7 @@ pub fn hasEnvVar(allocator: Allocator, key: []const u8) HasEnvVarError!bool {
     if (native_os == .windows) {
         var stack_alloc = std.heap.stackFallback(256 * @sizeOf(u16), allocator);
         const stack_allocator = stack_alloc.get();
-        const key_w = try std.unicode.wtf8ToWtf16LeAllocZ(stack_allocator, key);
+        const key_w = try unicode.wtf8ToWtf16LeAllocZ(stack_allocator, key);
         defer stack_allocator.free(key_w);
         return getenvW(key_w) != null;
     } else if (native_os == .wasi and !builtin.link_libc) {
@@ -659,7 +659,7 @@ pub const ArgIteratorWindows = struct {
     /// The iterator makes a copy of `cmd_line_w` converted WTF-8 and keeps it; it does *not* take
     /// ownership of `cmd_line_w`.
     pub fn init(allocator: Allocator, cmd_line_w: [*:0]const u16) InitError!ArgIteratorWindows {
-        const cmd_line = try std.unicode.wtf16LeToWtf8Alloc(allocator, mem.sliceTo(cmd_line_w, 0));
+        const cmd_line = try unicode.wtf16LeToWtf8Alloc(allocator, mem.sliceTo(cmd_line_w, 0));
         errdefer allocator.free(cmd_line);
 
         const buffer = try allocator.alloc(u8, cmd_line.len + 1);
@@ -728,17 +728,17 @@ pub const ArgIteratorWindows = struct {
             // must be 6 bytes for a surrogate pair to exist.
             if (self.end - self.start >= 6) {
                 const window = self.buffer[self.end - 6 .. self.end];
-                const view = std.unicode.Wtf8View.init(window) catch return;
+                const view = unicode.Wtf8View.init(window) catch return;
                 var it = view.iterator();
                 var pair: [2]u16 = undefined;
                 pair[0] = std.mem.nativeToLittle(u16, std.math.cast(u16, it.nextCodepoint().?) orelse return);
-                if (!std.unicode.utf16IsHighSurrogate(std.mem.littleToNative(u16, pair[0]))) return;
+                if (!unicode.utf16IsHighSurrogate(std.mem.littleToNative(u16, pair[0]))) return;
                 pair[1] = std.mem.nativeToLittle(u16, std.math.cast(u16, it.nextCodepoint().?) orelse return);
-                if (!std.unicode.utf16IsLowSurrogate(std.mem.littleToNative(u16, pair[1]))) return;
+                if (!unicode.utf16IsLowSurrogate(std.mem.littleToNative(u16, pair[1]))) return;
                 // We know we have a valid surrogate pair, so convert
                 // it to UTF-8, overwriting the surrogate pair's bytes
                 // and then chop off the extra bytes.
-                const len = std.unicode.utf16LeToUtf8(window, &pair) catch unreachable;
+                const len = unicode.utf16LeToUtf8(window, &pair) catch unreachable;
                 const delta = 6 - len;
                 self.end -= delta;
             }
@@ -1341,7 +1341,7 @@ test ArgIteratorWindows {
 }
 
 fn testArgIteratorWindows(cmd_line: []const u8, expected_args: []const []const u8) !void {
-    const cmd_line_w = try std.unicode.wtf8ToWtf16LeAllocZ(testing.allocator, cmd_line);
+    const cmd_line_w = try unicode.wtf8ToWtf16LeAllocZ(testing.allocator, cmd_line);
     defer testing.allocator.free(cmd_line_w);
 
     // next
@@ -1642,7 +1642,7 @@ pub fn execve(
 
     const envp = m: {
         if (env_map) |m| {
-            const envp_buf = try child_process.createNullDelimitedEnvMap(arena, m);
+            const envp_buf = try createNullDelimitedEnvMap(arena, m);
             break :m envp_buf.ptr;
         } else if (builtin.link_libc) {
             break :m std.c.environ;
@@ -1789,3 +1789,90 @@ pub fn raiseFileDescriptorLimit() void {
 test raiseFileDescriptorLimit {
     raiseFileDescriptorLimit();
 }
+
+pub fn createNullDelimitedEnvMap(arena: mem.Allocator, env_map: *const EnvMap) ![:null]?[*:0]u8 {
+    const envp_count = env_map.count();
+    const envp_buf = try arena.allocSentinel(?[*:0]u8, envp_count, null);
+    {
+        var it = env_map.iterator();
+        var i: usize = 0;
+        while (it.next()) |pair| : (i += 1) {
+            const env_buf = try arena.allocSentinel(u8, pair.key_ptr.len + pair.value_ptr.len + 1, 0);
+            @memcpy(env_buf[0..pair.key_ptr.len], pair.key_ptr.*);
+            env_buf[pair.key_ptr.len] = '=';
+            @memcpy(env_buf[pair.key_ptr.len + 1 ..][0..pair.value_ptr.len], pair.value_ptr.*);
+            envp_buf[i] = env_buf.ptr;
+        }
+        assert(i == envp_count);
+    }
+    return envp_buf;
+}
+
+test createNullDelimitedEnvMap {
+    const allocator = testing.allocator;
+    var envmap = EnvMap.init(allocator);
+    defer envmap.deinit();
+
+    try envmap.put("HOME", "/home/ifreund");
+    try envmap.put("WAYLAND_DISPLAY", "wayland-1");
+    try envmap.put("DISPLAY", ":1");
+    try envmap.put("DEBUGINFOD_URLS", " ");
+    try envmap.put("XCURSOR_SIZE", "24");
+
+    var arena = std.heap.ArenaAllocator.init(allocator);
+    defer arena.deinit();
+    const environ = try createNullDelimitedEnvMap(arena.allocator(), &envmap);
+
+    try testing.expectEqual(@as(usize, 5), environ.len);
+
+    inline for (.{
+        "HOME=/home/ifreund",
+        "WAYLAND_DISPLAY=wayland-1",
+        "DISPLAY=:1",
+        "DEBUGINFOD_URLS= ",
+        "XCURSOR_SIZE=24",
+    }) |target| {
+        for (environ) |variable| {
+            if (mem.eql(u8, mem.span(variable orelse continue), target)) break;
+        } else {
+            try testing.expect(false); // Environment variable not found
+        }
+    }
+}
+
+/// Caller must free result.
+pub fn createWindowsEnvBlock(allocator: mem.Allocator, env_map: *const EnvMap) ![]u16 {
+    // count bytes needed
+    const max_chars_needed = x: {
+        var max_chars_needed: usize = 4; // 4 for the final 4 null bytes
+        var it = env_map.iterator();
+        while (it.next()) |pair| {
+            // +1 for '='
+            // +1 for null byte
+            max_chars_needed += pair.key_ptr.len + pair.value_ptr.len + 2;
+        }
+        break :x max_chars_needed;
+    };
+    const result = try allocator.alloc(u16, max_chars_needed);
+    errdefer allocator.free(result);
+
+    var it = env_map.iterator();
+    var i: usize = 0;
+    while (it.next()) |pair| {
+        i += try unicode.wtf8ToWtf16Le(result[i..], pair.key_ptr.*);
+        result[i] = '=';
+        i += 1;
+        i += try unicode.wtf8ToWtf16Le(result[i..], pair.value_ptr.*);
+        result[i] = 0;
+        i += 1;
+    }
+    result[i] = 0;
+    i += 1;
+    result[i] = 0;
+    i += 1;
+    result[i] = 0;
+    i += 1;
+    result[i] = 0;
+    i += 1;
+    return try allocator.realloc(result, i);
+}
lib/std/std.zig
@@ -14,8 +14,6 @@ pub const BoundedArrayAligned = @import("bounded_array.zig").BoundedArrayAligned
 pub const Build = @import("Build.zig");
 pub const BufMap = @import("buf_map.zig").BufMap;
 pub const BufSet = @import("buf_set.zig").BufSet;
-/// Deprecated: use `process.Child`.
-pub const ChildProcess = @import("child_process.zig").ChildProcess;
 pub const StaticStringMap = static_string_map.StaticStringMap;
 pub const StaticStringMapWithEql = static_string_map.StaticStringMapWithEql;
 pub const DoublyLinkedList = @import("linked_list.zig").DoublyLinkedList;
src/link/Coff.zig
@@ -893,7 +893,7 @@ fn writeAtom(self: *Coff, atom_index: Atom.Index, code: []u8) !void {
     }
 }
 
-fn debugMem(allocator: Allocator, handle: std.ChildProcess.Id, pvaddr: std.os.windows.LPVOID, code: []const u8) !void {
+fn debugMem(allocator: Allocator, handle: std.process.Child.Id, pvaddr: std.os.windows.LPVOID, code: []const u8) !void {
     const buffer = try allocator.alloc(u8, code.len);
     defer allocator.free(buffer);
     const memread = try std.os.windows.ReadProcessMemory(handle, pvaddr, buffer);
@@ -901,7 +901,7 @@ fn debugMem(allocator: Allocator, handle: std.ChildProcess.Id, pvaddr: std.os.wi
     log.debug("in memory: {x}", .{std.fmt.fmtSliceHexLower(memread)});
 }
 
-fn writeMemProtected(handle: std.ChildProcess.Id, pvaddr: std.os.windows.LPVOID, code: []const u8) !void {
+fn writeMemProtected(handle: std.process.Child.Id, pvaddr: std.os.windows.LPVOID, code: []const u8) !void {
     const old_prot = try std.os.windows.VirtualProtectEx(handle, pvaddr, code.len, std.os.windows.PAGE_EXECUTE_WRITECOPY);
     try writeMem(handle, pvaddr, code);
     // TODO: We can probably just set the pages writeable and leave it at that without having to restore the attributes.
@@ -909,7 +909,7 @@ fn writeMemProtected(handle: std.ChildProcess.Id, pvaddr: std.os.windows.LPVOID,
     _ = try std.os.windows.VirtualProtectEx(handle, pvaddr, code.len, old_prot);
 }
 
-fn writeMem(handle: std.ChildProcess.Id, pvaddr: std.os.windows.LPVOID, code: []const u8) !void {
+fn writeMem(handle: std.process.Child.Id, pvaddr: std.os.windows.LPVOID, code: []const u8) !void {
     const amt = try std.os.windows.WriteProcessMemory(handle, pvaddr, code);
     if (amt != code.len) return error.InputOutput;
 }
@@ -1031,7 +1031,7 @@ fn resolveRelocs(self: *Coff, atom_index: Atom.Index, relocs: []*const Relocatio
     }
 }
 
-pub fn ptraceAttach(self: *Coff, handle: std.ChildProcess.Id) !void {
+pub fn ptraceAttach(self: *Coff, handle: std.process.Child.Id) !void {
     if (!is_hot_update_compatible) return;
 
     log.debug("attaching to process with handle {*}", .{handle});
@@ -1041,7 +1041,7 @@ pub fn ptraceAttach(self: *Coff, handle: std.ChildProcess.Id) !void {
     };
 }
 
-pub fn ptraceDetach(self: *Coff, handle: std.ChildProcess.Id) void {
+pub fn ptraceDetach(self: *Coff, handle: std.process.Child.Id) void {
     if (!is_hot_update_compatible) return;
 
     log.debug("detaching from process with handle {*}", .{handle});
src/link/Wasm.zig
@@ -3637,7 +3637,7 @@ fn linkWithLLD(wasm: *Wasm, arena: Allocator, prog_node: *std.Progress.Node) !vo
             // If possible, we run LLD as a child process because it does not always
             // behave properly as a library, unfortunately.
             // https://github.com/ziglang/zig/issues/3825
-            var child = std.ChildProcess.init(argv.items, arena);
+            var child = std.process.Child.init(argv.items, arena);
             if (comp.clang_passthrough_mode) {
                 child.stdin_behavior = .Inherit;
                 child.stdout_behavior = .Inherit;
src/Compilation.zig
@@ -1935,7 +1935,7 @@ pub fn getTarget(self: Compilation) Target {
 pub fn hotCodeSwap(
     comp: *Compilation,
     prog_node: *std.Progress.Node,
-    pid: std.ChildProcess.Id,
+    pid: std.process.Child.Id,
 ) !void {
     const lf = comp.bin_file.?;
     lf.child_pid = pid;
@@ -4614,7 +4614,7 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: *std.P
             log.warn("failed to delete '{s}': {s}", .{ dep_file_path, @errorName(err) });
         };
         if (std.process.can_spawn) {
-            var child = std.ChildProcess.init(argv.items, arena);
+            var child = std.process.Child.init(argv.items, arena);
             if (comp.clang_passthrough_mode) {
                 child.stdin_behavior = .Inherit;
                 child.stdout_behavior = .Inherit;
@@ -4972,7 +4972,7 @@ fn spawnZigRc(
     var node_name: std.ArrayListUnmanaged(u8) = .{};
     defer node_name.deinit(arena);
 
-    var child = std.ChildProcess.init(argv, arena);
+    var child = std.process.Child.init(argv, arena);
     child.stdin_behavior = .Ignore;
     child.stdout_behavior = .Pipe;
     child.stderr_behavior = .Pipe;
src/link.zig
@@ -72,7 +72,7 @@ pub const File = struct {
     /// Prevents other processes from clobbering files in the output directory
     /// of this linking operation.
     lock: ?Cache.Lock = null,
-    child_pid: ?std.ChildProcess.Id = null,
+    child_pid: ?std.process.Child.Id = null,
 
     pub const OpenOptions = struct {
         symbol_count_hint: u64 = 32,
@@ -529,7 +529,7 @@ pub const File = struct {
     } ||
         fs.File.WriteFileError ||
         fs.File.OpenError ||
-        std.ChildProcess.SpawnError ||
+        std.process.Child.SpawnError ||
         fs.Dir.CopyFileError;
 
     /// Commit pending changes and write headers. Takes into account final output mode
src/main.zig
@@ -4026,7 +4026,7 @@ fn serve(
     });
     defer server.deinit();
 
-    var child_pid: ?std.ChildProcess.Id = null;
+    var child_pid: ?std.process.Child.Id = null;
 
     var progress: std.Progress = .{
         .terminal = null,
@@ -4316,7 +4316,7 @@ fn runOrTest(
         const cmd = try std.mem.join(arena, " ", argv.items);
         fatal("the following command failed to execve with '{s}':\n{s}", .{ @errorName(err), cmd });
     } else if (process.can_spawn) {
-        var child = std.ChildProcess.init(argv.items, gpa);
+        var child = std.process.Child.init(argv.items, gpa);
         child.env_map = &env_map;
         child.stdin_behavior = .Inherit;
         child.stdout_behavior = .Inherit;
@@ -4379,7 +4379,7 @@ fn runOrTestHotSwap(
     arg_mode: ArgMode,
     all_args: []const []const u8,
     runtime_args_start: ?usize,
-) !std.ChildProcess.Id {
+) !std.process.Child.Id {
     const lf = comp.bin_file.?;
 
     const exe_path = switch (builtin.target.os.tag) {
@@ -4456,7 +4456,7 @@ fn runOrTestHotSwap(
             return pid;
         },
         else => {
-            var child = std.ChildProcess.init(argv.items, gpa);
+            var child = std.process.Child.init(argv.items, gpa);
 
             child.stdin_behavior = .Inherit;
             child.stdout_behavior = .Inherit;
@@ -5245,7 +5245,7 @@ fn cmdBuild(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
         }
 
         if (process.can_spawn) {
-            var child = std.ChildProcess.init(child_argv.items, gpa);
+            var child = std.process.Child.init(child_argv.items, gpa);
             child.stdin_behavior = .Inherit;
             child.stdout_behavior = .Inherit;
             child.stderr_behavior = .Inherit;
@@ -5549,7 +5549,7 @@ fn jitCmd(
         });
     }
 
-    var child = std.ChildProcess.init(child_argv.items, gpa);
+    var child = std.process.Child.init(child_argv.items, gpa);
     child.stdin_behavior = .Inherit;
     child.stdout_behavior = if (options.capture == null) .Inherit else .Pipe;
     child.stderr_behavior = .Inherit;
test/src/Cases.zig
@@ -1839,7 +1839,7 @@ fn runOneCase(
                     try comp.makeBinFileExecutable();
 
                     while (true) {
-                        break :x std.ChildProcess.run(.{
+                        break :x std.process.Child.run(.{
                             .allocator = allocator,
                             .argv = argv.items,
                             .cwd_dir = tmp.dir,
test/standalone/child_process/main.zig
@@ -13,7 +13,7 @@ pub fn main() !void {
     _ = it.next() orelse unreachable; // skip binary name
     const child_path = it.next() orelse unreachable;
 
-    var child = std.ChildProcess.init(&.{ child_path, "hello arg" }, gpa);
+    var child = std.process.Child.init(&.{ child_path, "hello arg" }, gpa);
     child.stdin_behavior = .Pipe;
     child.stdout_behavior = .Pipe;
     child.stderr_behavior = .Inherit;
test/standalone/windows_bat_args/fuzz.zig
@@ -87,7 +87,7 @@ fn testExecBat(allocator: std.mem.Allocator, bat: []const u8, args: []const []co
 
     const can_have_trailing_empty_args = std.mem.eql(u8, bat, "args3.bat");
 
-    const result = try std.ChildProcess.run(.{
+    const result = try std.process.Child.run(.{
         .allocator = allocator,
         .env_map = env,
         .argv = argv.items,
test/standalone/windows_bat_args/test.zig
@@ -109,7 +109,7 @@ fn testExecBat(allocator: std.mem.Allocator, bat: []const u8, args: []const []co
 
     const can_have_trailing_empty_args = std.mem.eql(u8, bat, "args3.bat");
 
-    const result = try std.ChildProcess.run(.{
+    const result = try std.process.Child.run(.{
         .allocator = allocator,
         .env_map = env,
         .argv = argv.items,
test/standalone/windows_spawn/main.zig
@@ -158,7 +158,7 @@ fn testExec(allocator: std.mem.Allocator, command: []const u8, expected_stdout:
 }
 
 fn testExecWithCwd(allocator: std.mem.Allocator, command: []const u8, cwd: ?[]const u8, expected_stdout: []const u8) !void {
-    const result = try std.ChildProcess.run(.{
+    const result = try std.process.Child.run(.{
         .allocator = allocator,
         .argv = &[_][]const u8{command},
         .cwd = cwd,
tools/docgen.zig
@@ -3,7 +3,7 @@ const builtin = @import("builtin");
 const io = std.io;
 const fs = std.fs;
 const process = std.process;
-const ChildProcess = std.ChildProcess;
+const ChildProcess = std.process.Child;
 const Progress = std.Progress;
 const print = std.debug.print;
 const mem = std.mem;
tools/generate_linux_syscalls.zig
@@ -257,7 +257,7 @@ pub fn main() !void {
             "arch/arm64/include/uapi/asm/unistd.h",
         };
 
-        const child_result = try std.ChildProcess.run(.{
+        const child_result = try std.process.Child.run(.{
             .allocator = allocator,
             .argv = &child_args,
             .cwd = linux_path,
@@ -318,7 +318,7 @@ pub fn main() !void {
             "arch/riscv/include/uapi/asm/unistd.h",
         };
 
-        const child_result = try std.ChildProcess.run(.{
+        const child_result = try std.process.Child.run(.{
             .allocator = allocator,
             .argv = &child_args,
             .cwd = linux_path,
tools/update_clang_options.zig
@@ -624,7 +624,7 @@ pub fn main() anyerror!void {
         try std.fmt.allocPrint(allocator, "-I={s}/clang/include/clang/Driver", .{llvm_src_root}),
     };
 
-    const child_result = try std.ChildProcess.run(.{
+    const child_result = try std.process.Child.run(.{
         .allocator = allocator,
         .argv = &child_args,
         .max_output_bytes = 100 * 1024 * 1024,
tools/update_cpu_features.zig
@@ -1106,7 +1106,7 @@ fn processOneTarget(job: Job) anyerror!void {
         }),
     };
 
-    const child_result = try std.ChildProcess.run(.{
+    const child_result = try std.process.Child.run(.{
         .allocator = arena,
         .argv = &child_args,
         .max_output_bytes = 400 * 1024 * 1024,
CMakeLists.txt
@@ -193,100 +193,6 @@ set(ZIG_CPP_SOURCES
 # Needed because we use cmake, not the zig build system, to build zig2.o.
 set(ZIG_STAGE2_SOURCES
     "${ZIG_CONFIG_ZIG_OUT}"
-    lib/std/array_hash_map.zig
-    lib/std/array_list.zig
-    lib/std/ascii.zig
-    lib/std/atomic.zig
-    lib/std/base64.zig
-    lib/std/BitStack.zig
-    lib/std/buf_map.zig
-    lib/std/Build.zig
-    lib/std/Build/Cache.zig
-    lib/std/Build/Cache/DepTokenizer.zig
-    lib/std/builtin.zig
-    lib/std/c.zig
-    lib/std/c/linux.zig
-    lib/std/child_process.zig
-    lib/std/coff.zig
-    lib/std/static_string_map.zig
-    lib/std/crypto.zig
-    lib/std/crypto/blake3.zig
-    lib/std/crypto/siphash.zig
-    lib/std/debug.zig
-    lib/std/dwarf.zig
-    lib/std/dwarf/AT.zig
-    lib/std/dwarf/ATE.zig
-    lib/std/dwarf/FORM.zig
-    lib/std/dwarf/LANG.zig
-    lib/std/dwarf/OP.zig
-    lib/std/dwarf/TAG.zig
-    lib/std/elf.zig
-    lib/std/fifo.zig
-    lib/std/fmt.zig
-    lib/std/fmt/format_float.zig
-    lib/std/fmt/parse_float.zig
-    lib/std/fs.zig
-    lib/std/fs/AtomicFile.zig
-    lib/std/fs/Dir.zig
-    lib/std/fs/File.zig
-    lib/std/fs/get_app_data_dir.zig
-    lib/std/fs/path.zig
-    lib/std/hash.zig
-    lib/std/hash/auto_hash.zig
-    lib/std/hash/wyhash.zig
-    lib/std/hash_map.zig
-    lib/std/heap.zig
-    lib/std/heap/arena_allocator.zig
-    lib/std/io.zig
-    lib/std/io/buffered_atomic_file.zig
-    lib/std/io/buffered_writer.zig
-    lib/std/io/change_detection_stream.zig
-    lib/std/io/counting_reader.zig
-    lib/std/io/counting_writer.zig
-    lib/std/io/find_byte_writer.zig
-    lib/std/io/fixed_buffer_stream.zig
-    lib/std/io/limited_reader.zig
-    lib/std/io/Reader.zig
-    lib/std/io/seekable_stream.zig
-    lib/std/io/Writer.zig
-    lib/std/json.zig
-    lib/std/json/stringify.zig
-    lib/std/leb128.zig
-    lib/std/linked_list.zig
-    lib/std/log.zig
-    lib/std/macho.zig
-    lib/std/math.zig
-    lib/std/math/big.zig
-    lib/std/math/big/int.zig
-    lib/std/math/float.zig
-    lib/std/math/frexp.zig
-    lib/std/math/isinf.zig
-    lib/std/math/isnan.zig
-    lib/std/math/log.zig
-    lib/std/math/log10.zig
-    lib/std/math/log2.zig
-    lib/std/math/signbit.zig
-    lib/std/math/sqrt.zig
-    lib/std/mem.zig
-    lib/std/mem/Allocator.zig
-    lib/std/meta.zig
-    lib/std/meta/trailer_flags.zig
-    lib/std/multi_array_list.zig
-    lib/std/os.zig
-    lib/std/os/linux.zig
-    lib/std/os/linux/x86_64.zig
-    lib/std/os/linux.zig
-    lib/std/os/linux/IoUring.zig
-    lib/std/os/linux/io_uring_sqe.zig
-    lib/std/os/linux/x86_64.zig
-    lib/std/os/windows.zig
-    lib/std/os/windows/ntstatus.zig
-    lib/std/os/windows/win32error.zig
-    lib/std/Progress.zig
-    lib/std/pdb.zig
-    lib/std/process.zig
-    lib/std/Random.zig
-    lib/std/sort.zig
     lib/compiler_rt.zig
     lib/compiler_rt/absv.zig
     lib/compiler_rt/absvdi2.zig
@@ -363,7 +269,7 @@ set(ZIG_STAGE2_SOURCES
     lib/compiler_rt/fixxfdi.zig
     lib/compiler_rt/fixxfsi.zig
     lib/compiler_rt/fixxfti.zig
-    lib/compiler_rt/int_from_float.zig
+    lib/compiler_rt/float_from_int.zig
     lib/compiler_rt/floatdidf.zig
     lib/compiler_rt/floatdihf.zig
     lib/compiler_rt/floatdisf.zig
@@ -404,7 +310,7 @@ set(ZIG_STAGE2_SOURCES
     lib/compiler_rt/getf2.zig
     lib/compiler_rt/gexf2.zig
     lib/compiler_rt/int.zig
-    lib/compiler_rt/float_from_int.zig
+    lib/compiler_rt/int_from_float.zig
     lib/compiler_rt/log.zig
     lib/compiler_rt/log10.zig
     lib/compiler_rt/log2.zig
@@ -417,7 +323,11 @@ set(ZIG_STAGE2_SOURCES
     lib/compiler_rt/multf3.zig
     lib/compiler_rt/mulxf3.zig
     lib/compiler_rt/negXi2.zig
+    lib/compiler_rt/negdf2.zig
+    lib/compiler_rt/negsf2.zig
+    lib/compiler_rt/negtf2.zig
     lib/compiler_rt/negv.zig
+    lib/compiler_rt/negxf2.zig
     lib/compiler_rt/os_version_check.zig
     lib/compiler_rt/parity.zig
     lib/compiler_rt/popcount.zig
@@ -430,15 +340,11 @@ set(ZIG_STAGE2_SOURCES
     lib/compiler_rt/sincos.zig
     lib/compiler_rt/sqrt.zig
     lib/compiler_rt/stack_probe.zig
+    lib/compiler_rt/subdf3.zig
     lib/compiler_rt/subo.zig
     lib/compiler_rt/subsf3.zig
-    lib/compiler_rt/subdf3.zig
     lib/compiler_rt/subtf3.zig
     lib/compiler_rt/subxf3.zig
-    lib/compiler_rt/negsf2.zig
-    lib/compiler_rt/negdf2.zig
-    lib/compiler_rt/negtf2.zig
-    lib/compiler_rt/negxf2.zig
     lib/compiler_rt/tan.zig
     lib/compiler_rt/trig.zig
     lib/compiler_rt/trunc.zig
@@ -461,8 +367,12 @@ set(ZIG_STAGE2_SOURCES
     lib/compiler_rt/unorddf2.zig
     lib/compiler_rt/unordsf2.zig
     lib/compiler_rt/unordtf2.zig
-    lib/std/start.zig
-    lib/std/std.zig
+    lib/std/BitStack.zig
+    lib/std/Build.zig
+    lib/std/Build/Cache.zig
+    lib/std/Build/Cache/DepTokenizer.zig
+    lib/std/Progress.zig
+    lib/std/Random.zig
     lib/std/Target.zig
     lib/std/Target/Query.zig
     lib/std/Target/aarch64.zig
@@ -476,8 +386,8 @@ set(ZIG_STAGE2_SOURCES
     lib/std/Target/nvptx.zig
     lib/std/Target/powerpc.zig
     lib/std/Target/riscv.zig
-    lib/std/Target/sparc.zig
     lib/std/Target/s390x.zig
+    lib/std/Target/sparc.zig
     lib/std/Target/wasm.zig
     lib/std/Target/x86.zig
     lib/std/Thread.zig
@@ -486,6 +396,96 @@ set(ZIG_STAGE2_SOURCES
     lib/std/Thread/Pool.zig
     lib/std/Thread/ResetEvent.zig
     lib/std/Thread/WaitGroup.zig
+    lib/std/array_hash_map.zig
+    lib/std/array_list.zig
+    lib/std/ascii.zig
+    lib/std/atomic.zig
+    lib/std/base64.zig
+    lib/std/buf_map.zig
+    lib/std/builtin.zig
+    lib/std/c.zig
+    lib/std/c/linux.zig
+    lib/std/coff.zig
+    lib/std/crypto.zig
+    lib/std/crypto/blake3.zig
+    lib/std/crypto/siphash.zig
+    lib/std/debug.zig
+    lib/std/dwarf.zig
+    lib/std/dwarf/AT.zig
+    lib/std/dwarf/ATE.zig
+    lib/std/dwarf/FORM.zig
+    lib/std/dwarf/LANG.zig
+    lib/std/dwarf/OP.zig
+    lib/std/dwarf/TAG.zig
+    lib/std/elf.zig
+    lib/std/fifo.zig
+    lib/std/fmt.zig
+    lib/std/fmt/format_float.zig
+    lib/std/fmt/parse_float.zig
+    lib/std/fs.zig
+    lib/std/fs/AtomicFile.zig
+    lib/std/fs/Dir.zig
+    lib/std/fs/File.zig
+    lib/std/fs/get_app_data_dir.zig
+    lib/std/fs/path.zig
+    lib/std/hash.zig
+    lib/std/hash/auto_hash.zig
+    lib/std/hash/wyhash.zig
+    lib/std/hash_map.zig
+    lib/std/heap.zig
+    lib/std/heap/arena_allocator.zig
+    lib/std/io.zig
+    lib/std/io/Reader.zig
+    lib/std/io/Writer.zig
+    lib/std/io/buffered_atomic_file.zig
+    lib/std/io/buffered_writer.zig
+    lib/std/io/change_detection_stream.zig
+    lib/std/io/counting_reader.zig
+    lib/std/io/counting_writer.zig
+    lib/std/io/find_byte_writer.zig
+    lib/std/io/fixed_buffer_stream.zig
+    lib/std/io/limited_reader.zig
+    lib/std/io/seekable_stream.zig
+    lib/std/json.zig
+    lib/std/json/stringify.zig
+    lib/std/leb128.zig
+    lib/std/linked_list.zig
+    lib/std/log.zig
+    lib/std/macho.zig
+    lib/std/math.zig
+    lib/std/math/big.zig
+    lib/std/math/big/int.zig
+    lib/std/math/float.zig
+    lib/std/math/frexp.zig
+    lib/std/math/isinf.zig
+    lib/std/math/isnan.zig
+    lib/std/math/log.zig
+    lib/std/math/log10.zig
+    lib/std/math/log2.zig
+    lib/std/math/signbit.zig
+    lib/std/math/sqrt.zig
+    lib/std/mem.zig
+    lib/std/mem/Allocator.zig
+    lib/std/meta.zig
+    lib/std/meta/trailer_flags.zig
+    lib/std/multi_array_list.zig
+    lib/std/os.zig
+    lib/std/os/linux.zig
+    lib/std/os/linux.zig
+    lib/std/os/linux/IoUring.zig
+    lib/std/os/linux/io_uring_sqe.zig
+    lib/std/os/linux/x86_64.zig
+    lib/std/os/linux/x86_64.zig
+    lib/std/os/windows.zig
+    lib/std/os/windows/ntstatus.zig
+    lib/std/os/windows/win32error.zig
+    lib/std/pdb.zig
+    lib/std/process.zig
+    lib/std/process/Child.zig
+    lib/std/sort.zig
+    lib/std/start.zig
+    lib/std/static_string_map.zig
+    lib/std/std.zig
     lib/std/time.zig
     lib/std/treap.zig
     lib/std/unicode.zig