fix: Fix normalization of extension paths on the annoying operating s…

…ystem and Python 3.13

Python 3.13 changed `os.path.isabs`:

> On Windows, `isabs()` no longer considers paths starting with exactly one slash (`\` or `/`) to be absolute.

See https://docs.python.org/3/whatsnew/3.13.html#os-path.

src/mkdocstrings_handlers/python/handler.py

@@ -469,11 +469,9 @@ def normalize_extension_paths(self, extensions: Sequence) -> Sequence:
                 pth = str(ext)
                 options = None
 
-            if pth.endswith(".py") or ".py:" in pth or "/" in pth or "\\" in pth:  # noqa: SIM102
-                # This is a sytem path. Normalize it.
-                if not os.path.isabs(pth):
-                    # Make path absolute relative to config file path.
-                    pth = os.path.normpath(os.path.join(base_path, pth))
+            if pth.endswith(".py") or ".py:" in pth or "/" in pth or "\\" in pth:
+                # This is a system path. Normalize it, make it absolute relative to config file path.
+                pth = os.path.abspath(os.path.join(base_path, pth))
 
             if options is not None:
                 normalized.append({pth: options})

tests/test_handler.py

@@ -138,10 +138,10 @@ def test_extension_paths(tmp_path: Path, expect_change: bool, extension: str | d
     normalized = handler.normalize_extension_paths([extension])[0]
     if expect_change:
         if isinstance(normalized, str) and isinstance(extension, str):
-            assert normalized == str(tmp_path.joinpath(extension))
+            assert normalized == os.fspath(tmp_path.joinpath(extension))
         elif isinstance(normalized, dict) and isinstance(extension, dict):
             pth, options = next(iter(extension.items()))
-            assert normalized == {str(tmp_path.joinpath(pth)): options}
+            assert normalized == {os.fspath(tmp_path.joinpath(pth)): options}
         else:
             raise ValueError("Normalization must not change extension items type")
     else: