pathlib ABCs: tighten up `resolve()` and `absolute()` (#126611)

In `PathBase.resolve()`, raise `UnsupportedOperation` if a non-POSIX path
parser is used (our implementation uses `posixpath._realpath()`, which
produces incorrect results for non-POSIX path flavours.) Also tweak code to
call `self.absolute()` upfront rather than supplying an emulated `getcwd()`
function.

Adjust `PathBase.absolute()` to work somewhat like `resolve()`. If a POSIX
path parser is used, we treat the root directory as the current directory.
This is the simplest useful behaviour for concrete path types without a
current directory cursor.

1 files changed, 22 insertions, 0 deletions

diff --git a/Lib/test/test_pathlib/test_pathlib.py b/Lib/test/test_pathlib/test_pathlib.py
index c7104bf..46966b6 100644
--- a/Lib/test/test_pathlib/test_pathlib.py
+++ b/Lib/test/test_pathlib/test_pathlib.py
@@ -861,6 +861,28 @@ class PathTest(test_pathlib_abc.DummyPathTest, PurePathTest):
     def test_move_into_empty_name_other_os(self):
         self.test_move_into_empty_name()
 
+    def _check_complex_symlinks(self, link0_target):
+        super()._check_complex_symlinks(link0_target)
+        P = self.cls(self.base)
+        # Resolve relative paths.
+        old_path = os.getcwd()
+        os.chdir(self.base)
+        try:
+            p = self.cls('link0').resolve()
+            self.assertEqual(p, P)
+            self.assertEqualNormCase(str(p), self.base)
+            p = self.cls('link1').resolve()
+            self.assertEqual(p, P)
+            self.assertEqualNormCase(str(p), self.base)
+            p = self.cls('link2').resolve()
+            self.assertEqual(p, P)
+            self.assertEqualNormCase(str(p), self.base)
+            p = self.cls('link3').resolve()
+            self.assertEqual(p, P)
+            self.assertEqualNormCase(str(p), self.base)
+        finally:
+            os.chdir(old_path)
+
     def test_resolve_nonexist_relative_issue38671(self):
         p = self.cls('non', 'exist')