From 349f7ae4e9b22f435538e4dd1eff1b88823a11b0 Mon Sep 17 00:00:00 2001
From: Mathieu Olivari <molivari@apple.com>
Date: Tue, 15 Sep 2026 12:53:19 +0100
Subject: [PATCH] Resolve system SDK path via xcrun in explicit-modules scan

The scanner assumed an unversioned SDK symlink (e.g. MacOSX.sdk) exists
under each platform's SDKs directory. That symlink is not guaranteed to
be present in every Xcode layout, causing scanning to fail with
FileNotFoundError.

Ask xcrun for the resolved SDK path instead, failing loudly if it cannot
be determined.
---
 tools/explicit_modules/scan.py | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/tools/explicit_modules/scan.py b/tools/explicit_modules/scan.py
index d5e25c412..e4178b806 100755
--- a/tools/explicit_modules/scan.py
+++ b/tools/explicit_modules/scan.py
@@ -736,6 +736,38 @@ def _parse_modulemap_for_modules(modulemap_path: Path) -> set[str]:
     return modules
 
 
+def _resolve_sdk_path(*, developer_dir: Path, sdk: str) -> Path:
+    """Resolves the concrete SDK path for `sdk` within `developer_dir`.
+
+    Xcode's `SDKs` directory normally contains an unversioned `<SDK>.sdk`
+    symlink (for example `MacOSX.sdk`) that points at the versioned SDK, but that
+    symlink is not guaranteed to exist in every Xcode layout. Ask `xcrun` for the
+    resolved path instead.
+    """
+    env = dict(os.environ)
+    env["DEVELOPER_DIR"] = developer_dir.as_posix()
+    try:
+        output = subprocess.check_output(
+            ["xcrun", "--sdk", sdk.lower(), "--show-sdk-path"],
+            env=env,
+            text=True,
+            stderr=subprocess.PIPE,
+        ).strip()
+    except (OSError, subprocess.CalledProcessError) as e:
+        stderr = getattr(e, "stderr", "") or ""
+        raise SystemExit(
+            f"error: could not resolve the {sdk} SDK path via xcrun "
+            f"(DEVELOPER_DIR={developer_dir}): {e}\n{stderr}"
+        )
+
+    if not output:
+        raise SystemExit(
+            f"error: `xcrun --sdk {sdk.lower()} --show-sdk-path` returned an "
+            f"empty path (DEVELOPER_DIR={developer_dir})"
+        )
+    return Path(output)
+
+
 def _discover_all_modules(
     developer_dir: Path,
     developer_dir_symlink_name: str,
@@ -743,7 +775,7 @@ def _discover_all_modules(
     excluded_modules: set[str],
 ) -> tuple[str, set[str]]:
     platform_developer_path = developer_dir / f"Platforms/{sdk}.platform/Developer"
-    sdk_path = platform_developer_path / f"SDKs/{sdk}.sdk"
+    sdk_path = _resolve_sdk_path(developer_dir=developer_dir, sdk=sdk)
     framework_search_paths = [
         platform_developer_path / "Library/Frameworks",
         sdk_path / "System/Library/Frameworks",