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, 17 insertions, 23 deletions

diff --git a/Lib/test/test_pathlib/test_pathlib_abc.py b/Lib/test/test_pathlib/test_pathlib_abc.py
index bb2e418..b69d674 100644
--- a/Lib/test/test_pathlib/test_pathlib_abc.py
+++ b/Lib/test/test_pathlib/test_pathlib_abc.py
@@ -2493,6 +2493,23 @@ class DummyPathTest(DummyPurePathTest):
         bad_link.symlink_to("bad" * 200)
         self.assertEqual(sorted(base.glob('**/*')), [bad_link])
 
+    @needs_posix
+    def test_absolute_posix(self):
+        P = self.cls
+        # The default implementation uses '/' as the current directory
+        self.assertEqual(str(P('').absolute()), '/')
+        self.assertEqual(str(P('a').absolute()), '/a')
+        self.assertEqual(str(P('a/b').absolute()), '/a/b')
+
+        self.assertEqual(str(P('/').absolute()), '/')
+        self.assertEqual(str(P('/a').absolute()), '/a')
+        self.assertEqual(str(P('/a/b').absolute()), '/a/b')
+
+        # '//'-prefixed absolute path (supported by POSIX).
+        self.assertEqual(str(P('//').absolute()), '//')
+        self.assertEqual(str(P('//a').absolute()), '//a')
+        self.assertEqual(str(P('//a/b').absolute()), '//a/b')
+
     @needs_symlinks
     def test_readlink(self):
         P = self.cls(self.base)
@@ -2810,29 +2827,6 @@ class DummyPathTest(DummyPurePathTest):
         self.assertEqual(p, P)
         self.assertEqualNormCase(str(p), self.base)
 
-        # Resolve relative paths.
-        try:
-            self.cls('').absolute()
-        except UnsupportedOperation:
-            return
-        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)
-
     @needs_symlinks
     def test_complex_symlinks_absolute(self):
         self._check_complex_symlinks(self.base)