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

2 files changed, 18 insertions, 0 deletions

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,
         }
     }