Commit c746d7a35d

@@ -0,0 +1,135 @@
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const test_step = b.step("test", "Test it");
+    b.default_step = test_step;
+
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+
+    const exe = b.addExecutable(.{
+        .name = "create-file",
+        .root_source_file = b.path("main.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+
+    {
+        const run_random_with_sideeffects_first = b.addRunArtifact(exe);
+        run_random_with_sideeffects_first.setName("run with side-effects (first)");
+        run_random_with_sideeffects_first.has_side_effects = true;
+
+        const run_random_with_sideeffects_second = b.addRunArtifact(exe);
+        run_random_with_sideeffects_second.setName("run with side-effects (second)");
+        run_random_with_sideeffects_second.has_side_effects = true;
+
+        // ensure that "second" runs after "first"
+        run_random_with_sideeffects_second.step.dependOn(&run_random_with_sideeffects_first.step);
+
+        const first_output = run_random_with_sideeffects_first.addOutputFileArg("a.txt");
+        const second_output = run_random_with_sideeffects_second.addOutputFileArg("a.txt");
+
+        const expect_uncached_dependencies = CheckOutputCaching.init(b, false, &.{ first_output, second_output });
+        test_step.dependOn(&expect_uncached_dependencies.step);
+
+        const expect_unequal_output = CheckPathEquality.init(b, true, &.{ first_output, second_output });
+        test_step.dependOn(&expect_unequal_output.step);
+
+        const check_first_output = b.addCheckFile(first_output, .{ .expected_matches = &.{"a.txt"} });
+        test_step.dependOn(&check_first_output.step);
+        const check_second_output = b.addCheckFile(second_output, .{ .expected_matches = &.{"a.txt"} });
+        test_step.dependOn(&check_second_output.step);
+    }
+
+    {
+        const run_random_without_sideeffects_1 = b.addRunArtifact(exe);
+        run_random_without_sideeffects_1.setName("run without side-effects (A)");
+
+        const run_random_without_sideeffects_2 = b.addRunArtifact(exe);
+        run_random_without_sideeffects_2.setName("run without side-effects (B)");
+
+        run_random_without_sideeffects_2.step.dependOn(&run_random_without_sideeffects_1.step);
+
+        const first_output = run_random_without_sideeffects_1.addOutputFileArg("a.txt");
+        const second_output = run_random_without_sideeffects_2.addOutputFileArg("a.txt");
+
+        const expect_cached_dependencies = CheckOutputCaching.init(b, true, &.{second_output});
+        test_step.dependOn(&expect_cached_dependencies.step);
+
+        const expect_equal_output = CheckPathEquality.init(b, true, &.{ first_output, second_output });
+        test_step.dependOn(&expect_equal_output.step);
+
+        const check_first_output = b.addCheckFile(first_output, .{ .expected_matches = &.{"a.txt"} });
+        test_step.dependOn(&check_first_output.step);
+        const check_second_output = b.addCheckFile(second_output, .{ .expected_matches = &.{"a.txt"} });
+        test_step.dependOn(&check_second_output.step);
+    }
+}
+
+const CheckOutputCaching = struct {
+    step: std.Build.Step,
+    expect_caching: bool,
+
+    pub fn init(owner: *std.Build, expect_caching: bool, output_paths: []const std.Build.LazyPath) *CheckOutputCaching {
+        const check = owner.allocator.create(CheckOutputCaching) catch @panic("OOM");
+        check.* = .{
+            .step = std.Build.Step.init(.{
+                .id = .custom,
+                .name = "check output caching",
+                .owner = owner,
+                .makeFn = make,
+            }),
+            .expect_caching = expect_caching,
+        };
+        for (output_paths) |output_path| {
+            output_path.addStepDependencies(&check.step);
+        }
+        return check;
+    }
+
+    fn make(step: *std.Build.Step, _: std.Progress.Node) !void {
+        const check: *CheckOutputCaching = @fieldParentPtr("step", step);
+
+        for (step.dependencies.items) |dependency| {
+            if (check.expect_caching) {
+                if (dependency.result_cached) continue;
+                return step.fail("expected '{s}' step to be cached, but it was not", .{dependency.name});
+            } else {
+                if (!dependency.result_cached) continue;
+                return step.fail("expected '{s}' step to not be cached, but it was", .{dependency.name});
+            }
+        }
+    }
+};
+
+const CheckPathEquality = struct {
+    step: std.Build.Step,
+    expected_equality: bool,
+    output_paths: []const std.Build.LazyPath,
+
+    pub fn init(owner: *std.Build, expected_equality: bool, output_paths: []const std.Build.LazyPath) *CheckPathEquality {
+        const check = owner.allocator.create(CheckPathEquality) catch @panic("OOM");
+        check.* = .{
+            .step = std.Build.Step.init(.{
+                .id = .custom,
+                .name = "check output path equality",
+                .owner = owner,
+                .makeFn = make,
+            }),
+            .expected_equality = expected_equality,
+            .output_paths = owner.allocator.dupe(std.Build.LazyPath, output_paths) catch @panic("OOM"),
+        };
+        for (output_paths) |output_path| {
+            output_path.addStepDependencies(&check.step);
+        }
+        return check;
+    }
+
+    fn make(step: *std.Build.Step, _: std.Progress.Node) !void {
+        const check: *CheckPathEquality = @fieldParentPtr("step", step);
+        std.debug.assert(check.output_paths.len != 0);
+        for (check.output_paths[0 .. check.output_paths.len - 1], check.output_paths[1..]) |a, b| {
+            try std.testing.expectEqual(check.expected_equality, std.mem.eql(u8, a.getPath(step.owner), b.getPath(step.owner)));
+        }
+    }
+};

@@ -0,0 +1,10 @@
+const std = @import("std");
+
+pub fn main() !void {
+    var args = try std.process.argsWithAllocator(std.heap.page_allocator);
+    _ = args.skip();
+    const filename = args.next().?;
+    const file = try std.fs.createFileAbsolute(filename, .{});
+    defer file.close();
+    try file.writeAll(filename);
+}

@@ -176,6 +176,9 @@
         .run_output_paths = .{
             .path = "run_output_paths",
         },
+        .run_output_caching = .{
+            .path = "run_output_caching",
+        },
     },
     .paths = .{
         "build.zig",