GH-110109: pathlib ABCs: do not vary path syntax by host OS. (#113219)

Change the value of `pathlib._abc.PurePathBase.pathmod` from `os.path` to
`posixpath`.

User subclasses of `PurePathBase` and `PathBase` previously used the host
OS's path syntax, e.g. backslashes as separators on Windows. This is wrong
in most use cases, and likely to catch developers out unless they test on
both Windows and non-Windows machines.

In this patch we change the default to POSIX syntax, regardless of OS. This
is somewhat arguable (why not make all aspects of syntax abstract and
individually configurable?) but an improvement all the same.

This change has no effect on `PurePath`, `Path`, nor their subclasses. Only
private APIs are affected.

1 files changed, 26 insertions, 58 deletions

diff --git a/Lib/test/test_pathlib/test_pathlib_abc.py b/Lib/test/test_pathlib/test_pathlib_abc.py
index 42575a5e640..37f4caa4da1 100644
--- a/Lib/test/test_pathlib/test_pathlib_abc.py
+++ b/Lib/test/test_pathlib/test_pathlib_abc.py
@@ -38,6 +38,9 @@ class PurePathBaseTest(unittest.TestCase):
         self.assertIs(P.__gt__, object.__gt__)
         self.assertIs(P.__ge__, object.__ge__)
 
+    def test_pathmod(self):
+        self.assertIs(self.cls.pathmod, posixpath)
+
 
 class DummyPurePath(pathlib._abc.PurePathBase):
     def __eq__(self, other):
@@ -52,8 +55,8 @@ class DummyPurePath(pathlib._abc.PurePathBase):
 class DummyPurePathTest(unittest.TestCase):
     cls = DummyPurePath
 
-    # Make sure any symbolic links in the base test path are resolved.
-    base = os.path.realpath(TESTFN)
+    # Use a base path that's unrelated to any real filesystem path.
+    base = f'/this/path/kills/fascists/{TESTFN}'
 
     # Keys are canonical paths, values are list of tuples of arguments
     # supposed to produce equal paths.
@@ -86,37 +89,6 @@ class DummyPurePathTest(unittest.TestCase):
         P('a/b/c')
         P('/a/b/c')
 
-    def test_concrete_class(self):
-        if self.cls is pathlib.PurePath:
-            expected = pathlib.PureWindowsPath if os.name == 'nt' else pathlib.PurePosixPath
-        else:
-            expected = self.cls
-        p = self.cls('a')
-        self.assertIs(type(p), expected)
-
-    def test_different_pathmods_unequal(self):
-        p = self.cls('a')
-        if p.pathmod is posixpath:
-            q = pathlib.PureWindowsPath('a')
-        else:
-            q = pathlib.PurePosixPath('a')
-        self.assertNotEqual(p, q)
-
-    def test_different_pathmods_unordered(self):
-        p = self.cls('a')
-        if p.pathmod is posixpath:
-            q = pathlib.PureWindowsPath('a')
-        else:
-            q = pathlib.PurePosixPath('a')
-        with self.assertRaises(TypeError):
-            p < q
-        with self.assertRaises(TypeError):
-            p <= q
-        with self.assertRaises(TypeError):
-            p > q
-        with self.assertRaises(TypeError):
-            p >= q
-
     def _check_str_subclass(self, *args):
         # Issue #21127: it should be possible to construct a PurePath object
         # from a str subclass instance, and it then gets converted to
@@ -721,15 +693,6 @@ class PathBaseTest(PurePathBaseTest):
     def test_as_bytes_common(self):
         self.assertRaises(TypeError, bytes, self.cls())
 
-    def test_matches_path_api(self):
-        our_names = {name for name in dir(self.cls) if name[0] != '_'}
-        path_names = {name for name in dir(pathlib.Path) if name[0] != '_'}
-        self.assertEqual(our_names, path_names)
-        for attr_name in our_names:
-            our_attr = getattr(self.cls, attr_name)
-            path_attr = getattr(pathlib.Path, attr_name)
-            self.assertEqual(our_attr.__doc__, path_attr.__doc__)
-
 
 class DummyPathIO(io.BytesIO):
     """
@@ -905,11 +868,13 @@ class DummyPathTest(DummyPurePathTest):
         self.assertEqual(cm.exception.errno, errno.ENOENT)
 
     def assertEqualNormCase(self, path_a, path_b):
-        self.assertEqual(os.path.normcase(path_a), os.path.normcase(path_b))
+        normcase = self.pathmod.normcase
+        self.assertEqual(normcase(path_a), normcase(path_b))
 
     def test_samefile(self):
-        fileA_path = os.path.join(self.base, 'fileA')
-        fileB_path = os.path.join(self.base, 'dirB', 'fileB')
+        pathmod = self.pathmod
+        fileA_path = pathmod.join(self.base, 'fileA')
+        fileB_path = pathmod.join(self.base, 'dirB', 'fileB')
         p = self.cls(fileA_path)
         pp = self.cls(fileA_path)
         q = self.cls(fileB_path)
@@ -918,7 +883,7 @@ class DummyPathTest(DummyPurePathTest):
         self.assertFalse(p.samefile(fileB_path))
         self.assertFalse(p.samefile(q))
         # Test the non-existent file case
-        non_existent = os.path.join(self.base, 'foo')
+        non_existent = pathmod.join(self.base, 'foo')
         r = self.cls(non_existent)
         self.assertRaises(FileNotFoundError, p.samefile, r)
         self.assertRaises(FileNotFoundError, p.samefile, non_existent)
@@ -1379,14 +1344,15 @@ class DummyPathTest(DummyPurePathTest):
             p.resolve(strict=True)
         self.assertEqual(cm.exception.errno, errno.ENOENT)
         # Non-strict
+        pathmod = self.pathmod
         self.assertEqualNormCase(str(p.resolve(strict=False)),
-                                 os.path.join(self.base, 'foo'))
+                                 pathmod.join(self.base, 'foo'))
         p = P(self.base, 'foo', 'in', 'spam')
         self.assertEqualNormCase(str(p.resolve(strict=False)),
-                                 os.path.join(self.base, 'foo', 'in', 'spam'))
+                                 pathmod.join(self.base, 'foo', 'in', 'spam'))
         p = P(self.base, '..', 'foo', 'in', 'spam')
         self.assertEqualNormCase(str(p.resolve(strict=False)),
-                                 os.path.abspath(os.path.join('foo', 'in', 'spam')))
+                                 pathmod.join(pathmod.dirname(self.base), 'foo', 'in', 'spam'))
         # These are all relative symlinks.
         p = P(self.base, 'dirB', 'fileB')
         self._check_resolve_relative(p, p)
@@ -1401,7 +1367,7 @@ class DummyPathTest(DummyPurePathTest):
         self._check_resolve_relative(p, P(self.base, 'dirB', 'fileB', 'foo', 'in',
                                           'spam'), False)
         p = P(self.base, 'dirA', 'linkC', '..', 'foo', 'in', 'spam')
-        if os.name == 'nt' and isinstance(p, pathlib.Path):
+        if self.cls.pathmod is not posixpath:
             # In Windows, if linkY points to dirB, 'dirA\linkY\..'
             # resolves to 'dirA' without resolving linkY first.
             self._check_resolve_relative(p, P(self.base, 'dirA', 'foo', 'in',
@@ -1421,7 +1387,7 @@ class DummyPathTest(DummyPurePathTest):
         self._check_resolve_relative(p, P(self.base, 'dirB', 'foo', 'in', 'spam'),
                                      False)
         p = P(self.base, 'dirA', 'linkX', 'linkY', '..', 'foo', 'in', 'spam')
-        if os.name == 'nt' and isinstance(p, pathlib.Path):
+        if self.cls.pathmod is not posixpath:
             # In Windows, if linkY points to dirB, 'dirA\linkY\..'
             # resolves to 'dirA' without resolving linkY first.
             self._check_resolve_relative(p, P(d, 'foo', 'in', 'spam'), False)
@@ -1434,10 +1400,11 @@ class DummyPathTest(DummyPurePathTest):
         # See http://web.archive.org/web/20200623062557/https://bitbucket.org/pitrou/pathlib/issues/9/
         if not self.can_symlink:
             self.skipTest("symlinks required")
+        pathmod = self.pathmod
         p = self.cls(self.base)
         p.joinpath('0').symlink_to('.', target_is_directory=True)
-        p.joinpath('1').symlink_to(os.path.join('0', '0'), target_is_directory=True)
-        p.joinpath('2').symlink_to(os.path.join('1', '1'), target_is_directory=True)
+        p.joinpath('1').symlink_to(pathmod.join('0', '0'), target_is_directory=True)
+        p.joinpath('2').symlink_to(pathmod.join('1', '1'), target_is_directory=True)
         q = p / '2'
         self.assertEqual(q.resolve(strict=True), p)
         r = q / '3' / '4'
@@ -1454,7 +1421,7 @@ class DummyPathTest(DummyPurePathTest):
     def test_resolve_loop(self):
         if not self.can_symlink:
             self.skipTest("symlinks required")
-        if os.name == 'nt' and issubclass(self.cls, pathlib.Path):
+        if self.cls.pathmod is not posixpath:
             self.skipTest("symlink loops work differently with concrete Windows paths")
         # Loops with relative symlinks.
         self.cls(self.base, 'linkX').symlink_to('linkX/inside')
@@ -1657,10 +1624,11 @@ class DummyPathTest(DummyPurePathTest):
             self.skipTest("symlinks required")
 
         # Test solving a non-looping chain of symlinks (issue #19887).
+        pathmod = self.pathmod
         P = self.cls(self.base)
-        P.joinpath('link1').symlink_to(os.path.join('link0', 'link0'), target_is_directory=True)
-        P.joinpath('link2').symlink_to(os.path.join('link1', 'link1'), target_is_directory=True)
-        P.joinpath('link3').symlink_to(os.path.join('link2', 'link2'), target_is_directory=True)
+        P.joinpath('link1').symlink_to(pathmod.join('link0', 'link0'), target_is_directory=True)
+        P.joinpath('link2').symlink_to(pathmod.join('link1', 'link1'), target_is_directory=True)
+        P.joinpath('link3').symlink_to(pathmod.join('link2', 'link2'), target_is_directory=True)
         P.joinpath('link0').symlink_to(link0_target, target_is_directory=True)
 
         # Resolve absolute paths.
@@ -1707,7 +1675,7 @@ class DummyPathTest(DummyPurePathTest):
         self._check_complex_symlinks('.')
 
     def test_complex_symlinks_relative_dot_dot(self):
-        self._check_complex_symlinks(os.path.join('dirA', '..'))
+        self._check_complex_symlinks(self.pathmod.join('dirA', '..'))
 
     def setUpWalk(self):
         # Build: