scanner: Fix error on Windows in case source files are on different drives

os.path.commonpath() raises ValueError if the paths given to it are on different
drives.

Handle that case by giving up and add a test.

Reported here: https://github.com/msys2/MINGW-packages/pull/5258#issuecomment-485230864

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/scanner/test_scanner.py b/tests/scanner/test_scanner.py
index 2513c0de..85953964 100644
--- a/tests/scanner/test_scanner.py
+++ b/tests/scanner/test_scanner.py
@@ -25,6 +25,16 @@ class TestScanner(unittest.TestCase):
         paths = get_source_root_dirs(options, [])
         self.assertEqual(paths, [])
 
+    @unittest.skipUnless(os.name == "nt", "Windows only")
+    def test_get_source_root_dirs_different_drives(self):
+        options = optparse.Values({"sources_top_dirs": []})
+        names = [
+            os.path.join("X:", os.sep, "foo"),
+            os.path.join("Y:", os.sep, "bar"),
+        ]
+        paths = get_source_root_dirs(options, names)
+        self.assertEqual(paths, list(map(os.path.dirname, names)))
+
 
 if __name__ == '__main__':
     unittest.main()