Commit 3ad9349f09

@@ -20,6 +20,33 @@ pub const shell32 = @import("windows/shell32.zig");
 
 pub usingnamespace @import("windows/bits.zig");
 
+/// `builtin` is missing `subsystem` when the subsystem is automatically detected,
+/// so Zig standard library has the subsystem detection logic here. This should generally be
+/// used rather than `builtin.subsystem`.
+/// On non-windows targets, this is `null`.
+pub const subsystem: ?builtin.SubSystem = blk: {
+    if (@hasDecl(builtin, "subsystem")) break :blk builtin.subsystem;
+    switch (builtin.os) {
+        .windows => {
+            if (builtin.is_test) {
+                break :blk builtin.SubSystem.Console;
+            }
+            const root = @import("root");
+            if (@hasDecl(root, "WinMain") or
+                @hasDecl(root, "wWinMain") or
+                @hasDecl(root, "WinMainCRTStartup") or
+                @hasDecl(root, "wWinMainCRTStartup"))
+            {
+                break :blk builtin.SubSystem.Windows;
+            } else {
+                break :blk builtin.SubSystem.Console;
+            }
+        },
+        .uefi => break :blk builtin.SubSystem.EfiApplication,
+        else => break :blk null,
+    }
+};
+
 pub const CreateFileError = error{
     SharingViolation,
     PathAlreadyExists,