Rewrite CacheDir _mkdir_atomic to include old version

The failure on Python 3.7 caused a rewrite. Redo that so the version
released with SCons 4.9.0 is still present, but commented out, so it's
easier to restore it in future.  tempfile.TemporaryDirectory has better
cleanup logic, so we'll want to flip to that when Python 3.7 support
is retired.

Signed-off-by: Mats Wichmann <[email protected]>

Author: mwichmann

SCons/CacheDir.py

@@ -209,14 +209,31 @@ def _mkdir_atomic(self, path: str) -> bool:
         if os.path.exists(directory):
             return False
 
-        # TODO: tried to use TemporaryDirectory() here and the result as a
-        #   context manager, but that fails on Python 3.7 (works on 3.8+) after
-        #   the directory has successfully been renamed. Not sure why.
         try:
+            # TODO: Python 3.7. See comment below.
+            # tempdir = tempfile.TemporaryDirectory(dir=os.path.dirname(directory))
             tempdir = tempfile.mkdtemp(dir=os.path.dirname(directory))
         except OSError as e:
             msg = "Failed to create cache directory " + path
             raise SCons.Errors.SConsEnvironmentError(msg) from e
+
+        # TODO: Python 3.7: the context manager raises exception on cleanup
+        #    if the temporary was moved successfully (File Not Found).
+        #    Fixed in 3.8+. In the replacement below we manually clean up if
+        #    the move failed as mkdtemp() does not. TemporaryDirectory's
+        #    cleanup is more sophisitcated so prefer when we can use it.
+        # self._add_config(tempdir.name)
+        # with tempdir:
+        #     try:
+        #         os.replace(tempdir.name, directory)
+        #         return True
+        #     except OSError as e:
+        #         # did someone else get there first?
+        #         if os.path.isdir(directory):
+        #             return False  # context manager cleans up
+        #         msg = "Failed to create cache directory " + path
+        #         raise SCons.Errors.SConsEnvironmentError(msg) from e
+
         self._add_config(tempdir)
         try:
             os.replace(tempdir, directory)