Try audodetecting sysroot when building Darwin on Darwin

This is now no longer limited to targeting macOS natively but also
tries to detect the sysroot when targeting different Apple platforms
from macOS; for instance targeting iPhone Simulator from macOS. In
this case, Zig will try detecting the SDK path by invoking
`xcrun --sdk iphonesimulator --show-sdk-path`, and if the command
fails because the SDK doesn't exist (case when having CLT installed only)
or not having either Xcode or CLT installed, we simply return null
signaling that the user has to provide the sysroot themselves.

1 files changed, 11 insertions, 7 deletions

diff --git a/src/main.zig b/src/main.zig
index 73c4560ddf..285b6d2316 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1678,7 +1678,9 @@ fn buildOutputType(
             want_native_include_dirs = true;
     }
 
-    if (sysroot == null and cross_target.isNativeOs() and
+    const is_darwin_on_darwin = (comptime std.Target.current.isDarwin()) and cross_target.isDarwin();
+
+    if (sysroot == null and (cross_target.isNativeOs() or is_darwin_on_darwin) and
         (system_libs.items.len != 0 or want_native_include_dirs))
     {
         const paths = std.zig.system.NativePaths.detect(arena, target_info) catch |err| {
@@ -1689,16 +1691,18 @@ fn buildOutputType(
         }
 
         const has_sysroot = if (comptime std.Target.current.isDarwin()) outer: {
-            const min = target_info.target.os.getVersionRange().semver.min;
-            const at_least_mojave = min.major >= 11 or (min.major >= 10 and min.minor >= 14);
-            if (at_least_mojave) {
-                const sdk_path = try std.zig.system.getSDKPath(arena);
+            const should_get_sdk_path = if (cross_target.isNativeOs() and target_info.target.os.tag == .macos) inner: {
+                const min = target_info.target.os.getVersionRange().semver.min;
+                const at_least_mojave = min.major >= 11 or (min.major >= 10 and min.minor >= 14);
+                break :inner at_least_mojave;
+            } else true;
+            if (!should_get_sdk_path) break :outer false;
+            if (try std.zig.system.darwin.getSDKPath(arena, target_info.target)) |sdk_path| {
                 try clang_argv.ensureCapacity(clang_argv.items.len + 2);
                 clang_argv.appendAssumeCapacity("-isysroot");
                 clang_argv.appendAssumeCapacity(sdk_path);
                 break :outer true;
-            }
-            break :outer false;
+            } else break :outer false;
         } else false;
 
         try clang_argv.ensureCapacity(clang_argv.items.len + paths.include_dirs.items.len * 2);