bpo-45192: Fix a bug that infers the type of an os.PathLike[bytes] object as str (GH-28323) (GH-29111)

An object implementing the os.PathLike protocol can represent a file
system path as a str or bytes object.
Therefore, _infer_return_type function should infer os.PathLike[str]
object as str type and os.PathLike[bytes] object as bytes type.
(cherry picked from commit 6270d3eeaf17b50abc4f8f4d97790d66179638e4)

Co-authored-by: Kyungmin Lee <rekyungmin@gmail.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index 96946a281a..2b0ec46a10 100644
--- a/Lib/test/test_tempfile.py
+++ b/Lib/test/test_tempfile.py
@@ -62,6 +62,25 @@ class TestLowLevelInternals(unittest.TestCase):
     def test_infer_return_type_pathlib(self):
         self.assertIs(str, tempfile._infer_return_type(pathlib.Path('/')))
 
+    def test_infer_return_type_pathlike(self):
+        class Path:
+            def __init__(self, path):
+                self.path = path
+
+            def __fspath__(self):
+                return self.path
+
+        self.assertIs(str, tempfile._infer_return_type(Path('/')))
+        self.assertIs(bytes, tempfile._infer_return_type(Path(b'/')))
+        self.assertIs(str, tempfile._infer_return_type('', Path('')))
+        self.assertIs(bytes, tempfile._infer_return_type(b'', Path(b'')))
+        self.assertIs(bytes, tempfile._infer_return_type(None, Path(b'')))
+        self.assertIs(str, tempfile._infer_return_type(None, Path('')))
+
+        with self.assertRaises(TypeError):
+            tempfile._infer_return_type('', Path(b''))
+        with self.assertRaises(TypeError):
+            tempfile._infer_return_type(b'', Path(''))
 
 # Common functionality.