TOOLS: add macos-swift-lib-directory.py script

Apple is great and forces us to do a lot of weird checks because they
randomly move the location of the swift libraries around. Make a
specific python script for checking various locations and write the
output to stdout for meson.

TOOLS/macos-swift-lib-directory.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+
+# Finds the macos swift library directory and prints the full path to stdout.
+# First argument is the path to the swift executable.
+
+import os
+import sys
+from shutil import which
+from subprocess import check_output
+
+def find_swift_lib():
+    swift_lib_dir = os.environ.get('SWIFT_LIB_DYNAMIC', '')
+    if swift_lib_dir:
+        return swift_lib_dir
+
+    # first check for lib dir relative to swift executable
+    xcode_dir = os.path.dirname(os.path.dirname(sys.argv[1]))
+    swift_lib_dir = os.path.join(xcode_dir, "lib", "swift", "macosx")
+
+    if os.path.isdir(swift_lib_dir):
+        return swift_lib_dir
+
+    # fallback to xcode-select path
+    xcode_select = which("xcode-select")
+    if not xcode_select:
+        sys.exit(1)
+
+    xcode_path = check_output([xcode_select, "-p"], encoding="UTF-8")
+
+    swift_lib_dir = os.path.join(xcode_path, "Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx")
+    if os.path.isdir(swift_lib_dir):
+        return swift_lib_dir
+
+    # last resort if we still haven't found a path
+    swift_lib_dir = os.path.join(xcode_path, "usr/lib/swift/macosx")
+    if not os.path.isdir(swift_lib_dir):
+        sys.exit(1)
+    return swift_lib_dir
+
+if __name__ == "__main__":
+    swift_lib_dir = find_swift_lib()
+    sys.stdout.write(swift_lib_dir)