Add experimental Darling support for cross testing macOS

* for cross testing stage2 tests, we use `darling shell` command
  since the path to the tested binary is relative to cwd
* for the `zig test` command, we simply use `darling` since the
  path to the binary is absolute

5 files changed, 99 insertions, 6 deletions

diff --git a/build.zig b/build.zig
index d31e218056..d3e02bba5e 100644
--- a/build.zig
+++ b/build.zig
@@ -218,6 +218,7 @@ pub fn build(b: *Builder) !void {
     const is_wine_enabled = b.option(bool, "enable-wine", "Use Wine to run cross compiled Windows tests") orelse false;
     const is_qemu_enabled = b.option(bool, "enable-qemu", "Use QEMU to run cross compiled foreign architecture tests") orelse false;
     const is_wasmtime_enabled = b.option(bool, "enable-wasmtime", "Use Wasmtime to enable and run WASI libstd tests") orelse false;
+    const is_darling_enabled = b.option(bool, "enable-darling", "[Experimental] Use Darling to run cross compiled macOS tests") orelse false;
     const glibc_multi_dir = b.option([]const u8, "enable-foreign-glibc", "Provide directory with glibc installations to run cross compiled tests that link glibc");
 
     test_stage2.addBuildOption(bool, "skip_non_native", skip_non_native);
@@ -227,6 +228,7 @@ pub fn build(b: *Builder) !void {
     test_stage2.addBuildOption(bool, "enable_qemu", is_qemu_enabled);
     test_stage2.addBuildOption(bool, "enable_wine", is_wine_enabled);
     test_stage2.addBuildOption(bool, "enable_wasmtime", is_wasmtime_enabled);
+    test_stage2.addBuildOption(bool, "enable_darling", is_darling_enabled);
     test_stage2.addBuildOption(?[]const u8, "glibc_multi_install_dir", glibc_multi_dir);
     test_stage2.addBuildOption([]const u8, "version", version);
 
@@ -261,11 +263,56 @@ pub fn build(b: *Builder) !void {
     const fmt_step = b.step("test-fmt", "Run zig fmt against build.zig to make sure it works");
     fmt_step.dependOn(&fmt_build_zig.step);
 
-    // TODO for the moment, skip wasm32-wasi until bugs are sorted out.
-    toolchain_step.dependOn(tests.addPkgTests(b, test_filter, "test/stage1/behavior.zig", "behavior", "Run the behavior tests", modes, false, skip_non_native, skip_libc, is_wine_enabled, is_qemu_enabled, is_wasmtime_enabled, glibc_multi_dir));
-
-    toolchain_step.dependOn(tests.addPkgTests(b, test_filter, "lib/std/special/compiler_rt.zig", "compiler-rt", "Run the compiler_rt tests", modes, true, skip_non_native, true, is_wine_enabled, is_qemu_enabled, is_wasmtime_enabled, glibc_multi_dir));
-    toolchain_step.dependOn(tests.addPkgTests(b, test_filter, "lib/std/special/c.zig", "minilibc", "Run the mini libc tests", modes, true, skip_non_native, true, is_wine_enabled, is_qemu_enabled, is_wasmtime_enabled, glibc_multi_dir));
+    toolchain_step.dependOn(tests.addPkgTests(
+        b,
+        test_filter,
+        "test/stage1/behavior.zig",
+        "behavior",
+        "Run the behavior tests",
+        modes,
+        false,
+        skip_non_native,
+        skip_libc,
+        is_wine_enabled,
+        is_qemu_enabled,
+        is_wasmtime_enabled,
+        is_darling_enabled,
+        glibc_multi_dir,
+    ));
+
+    toolchain_step.dependOn(tests.addPkgTests(
+        b,
+        test_filter,
+        "lib/std/special/compiler_rt.zig",
+        "compiler-rt",
+        "Run the compiler_rt tests",
+        modes,
+        true,
+        skip_non_native,
+        true,
+        is_wine_enabled,
+        is_qemu_enabled,
+        is_wasmtime_enabled,
+        is_darling_enabled,
+        glibc_multi_dir,
+    ));
+
+    toolchain_step.dependOn(tests.addPkgTests(
+        b,
+        test_filter,
+        "lib/std/special/c.zig",
+        "minilibc",
+        "Run the mini libc tests",
+        modes,
+        true,
+        skip_non_native,
+        true,
+        is_wine_enabled,
+        is_qemu_enabled,
+        is_wasmtime_enabled,
+        is_darling_enabled,
+        glibc_multi_dir,
+    ));
 
     toolchain_step.dependOn(tests.addCompareOutputTests(b, test_filter, modes));
     toolchain_step.dependOn(tests.addStandaloneTests(b, test_filter, modes));
@@ -283,7 +330,22 @@ pub fn build(b: *Builder) !void {
         toolchain_step.dependOn(tests.addCompileErrorTests(b, test_filter, modes));
     }
 
-    const std_step = tests.addPkgTests(b, test_filter, "lib/std/std.zig", "std", "Run the standard library tests", modes, false, skip_non_native, skip_libc, is_wine_enabled, is_qemu_enabled, is_wasmtime_enabled, glibc_multi_dir);
+    const std_step = tests.addPkgTests(
+        b,
+        test_filter,
+        "lib/std/std.zig",
+        "std",
+        "Run the standard library tests",
+        modes,
+        false,
+        skip_non_native,
+        skip_libc,
+        is_wine_enabled,
+        is_qemu_enabled,
+        is_wasmtime_enabled,
+        is_darling_enabled,
+        glibc_multi_dir,
+    );
 
     const test_step = b.step("test", "Run all the tests");
     test_step.dependOn(toolchain_step);
diff --git a/lib/std/build.zig b/lib/std/build.zig
index 9d12a4de51..808f3374d8 100644
--- a/lib/std/build.zig
+++ b/lib/std/build.zig
@@ -1398,6 +1398,9 @@ pub const LibExeObjStep = struct {
     /// Uses system Wasmtime installation to run cross compiled wasm/wasi build artifacts.
     enable_wasmtime: bool = false,
 
+    /// Experimental. Uses system Darling installation to run cross compiled macOS build artifacts.
+    enable_darling: bool = false,
+
     /// After following the steps in https://github.com/ziglang/zig/wiki/Updating-libc#glibc,
     /// this will be the directory $glibc-build-dir/install/glibcs
     /// Given the example of the aarch64 target, this is the directory
@@ -2514,6 +2517,11 @@ pub const LibExeObjStep = struct {
                 try zig_args.append("--dir=.");
                 try zig_args.append("--test-cmd-bin");
             },
+            .darling => |bin_name| if (self.enable_darling) {
+                try zig_args.append("--test-cmd");
+                try zig_args.append(bin_name);
+                try zig_args.append("--test-cmd-bin");
+            },
         }
 
         for (self.packages.items) |pkg| {
diff --git a/lib/std/zig/cross_target.zig b/lib/std/zig/cross_target.zig
index bf62a49ef6..e724be17ae 100644
--- a/lib/std/zig/cross_target.zig
+++ b/lib/std/zig/cross_target.zig
@@ -606,6 +606,7 @@ pub const CrossTarget = struct {
         qemu: []const u8,
         wine: []const u8,
         wasmtime: []const u8,
+        darling: []const u8,
         unavailable,
     };
 
@@ -667,6 +668,15 @@ pub const CrossTarget = struct {
                 32 => return Executor{ .wasmtime = "wasmtime" },
                 else => return .unavailable,
             },
+            .macos => {
+                // TODO loosen this check once upstream adds QEMU-based emulation
+                // layer for non-host architectures:
+                // https://github.com/darlinghq/darling/issues/863
+                if (cpu_arch != Target.current.cpu.arch) {
+                    return .unavailable;
+                }
+                return Executor{ .darling = "darling" };
+            },
             else => return .unavailable,
         }
     }
diff --git a/src/test.zig b/src/test.zig
index f1cf543252..5a8adca3c7 100644
--- a/src/test.zig
+++ b/src/test.zig
@@ -9,6 +9,7 @@ const build_options = @import("build_options");
 const enable_qemu: bool = build_options.enable_qemu;
 const enable_wine: bool = build_options.enable_wine;
 const enable_wasmtime: bool = build_options.enable_wasmtime;
+const enable_darling: bool = build_options.enable_darling;
 const glibc_multi_install_dir: ?[]const u8 = build_options.glibc_multi_install_dir;
 const ThreadPool = @import("ThreadPool.zig");
 const CrossTarget = std.zig.CrossTarget;
@@ -899,6 +900,16 @@ pub const TestContext = struct {
                             } else {
                                 return; // wasmtime not available; pass test.
                             },
+
+                            .darling => |darling_bin_name| if (enable_darling) {
+                                try argv.append(darling_bin_name);
+                                // Since we use relative to cwd here, we invoke darling with
+                                // "shell" subcommand.
+                                try argv.append("shell");
+                                try argv.append(exe_path);
+                            } else {
+                                return; // Darling not available; pass test.
+                            },
                         }
 
                         try comp.makeBinFileExecutable();
diff --git a/test/tests.zig b/test/tests.zig
index 8bd1f3528e..eca81b591f 100644
--- a/test/tests.zig
+++ b/test/tests.zig
@@ -503,6 +503,7 @@ pub fn addPkgTests(
     is_wine_enabled: bool,
     is_qemu_enabled: bool,
     is_wasmtime_enabled: bool,
+    is_darling_enabled: bool,
     glibc_dir: ?[]const u8,
 ) *build.Step {
     const step = b.step(b.fmt("test-{s}", .{name}), desc);
@@ -564,6 +565,7 @@ pub fn addPkgTests(
         these_tests.enable_wine = is_wine_enabled;
         these_tests.enable_qemu = is_qemu_enabled;
         these_tests.enable_wasmtime = is_wasmtime_enabled;
+        these_tests.enable_darling = is_darling_enabled;
         these_tests.glibc_multi_install_dir = glibc_dir;
         these_tests.addIncludeDir("test");