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

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.

Lib/tempfile.py

@@ -88,6 +88,10 @@ def _infer_return_type(*args):
     for arg in args:
         if arg is None:
             continue
+
+        if isinstance(arg, _os.PathLike):
+            arg = _os.fspath(arg)
+
         if isinstance(arg, bytes):
             if return_type is str:
                 raise TypeError("Can't mix bytes and non-bytes in "

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.
 

Misc/NEWS.d/next/Library/2021-09-14-15-52-47.bpo-45192.DjA-BI.rst

@@ -0,0 +1,5 @@
+Fix the ``tempfile._infer_return_type`` function so that the ``dir``
+argument of the :mod:`tempfile` functions accepts an object implementing the
+``os.PathLike`` protocol.
+
+Patch by Kyungmin Lee.