fix: resolve PUBLIC before looking up the user home

docs/changelog.rst

@@ -6,21 +6,21 @@
 
 .. towncrier release notes start
 
-********************
+*********************
  4.11.8 (2026-09-08)
-********************
+*********************
 
 - Make :func:`~platformdirs.user_data_path`, :func:`~platformdirs.user_config_path`,
-  :func:`~platformdirs.user_preference_path` and :func:`~platformdirs.user_applications_path` return the first site entry
-  when root is redirected by ``use_site_for_root`` under ``multipath``, matching their ``site_*_path`` twins. They passed
-  the whole joined list to :class:`~pathlib.Path`, giving one unusable path such as ``/xdg/a/foo:/xdg/b/foo`` - by
-  :user:`darrenhuai`. :pr:`538`
+  :func:`~platformdirs.user_preference_path` and :func:`~platformdirs.user_applications_path` return the first site
+  entry when root is redirected by ``use_site_for_root`` under ``multipath``, matching their ``site_*_path`` twins. They
+  passed the whole joined list to :class:`~pathlib.Path`, giving one unusable path such as ``/xdg/a/foo:/xdg/b/foo`` -
+  by :user:`darrenhuai`. :pr:`538`
 - Ignore relative paths in XDG Base Directory environment variables and use the existing platform fallback. Relative
   entries in ``$XDG_DATA_DIRS`` and ``$XDG_CONFIG_DIRS`` are skipped. :pr:`540`
 - Preserve literal percent signs in Unix ``user-dirs.dirs`` paths, including ``100% complete``, ``100%%`` and
   ``%(XDG_DESKTOP_DIR)s``. Continue to expand ``$HOME``. :pr:`542`
-- Use the base Python installation to locate Homebrew site directories on macOS, preserving shared data, config, cache and
-  state paths inside virtual environments. :pr:`543`
+- Use the base Python installation to locate Homebrew site directories on macOS, preserving shared data, config, cache
+  and state paths inside virtual environments. :pr:`543`
 
 *********************
  4.11.7 (2026-09-01)

docs/changelog/546.bugfix.rst

@@ -0,0 +1 @@
+Resolve ``user_publicshare_dir`` from ``PUBLIC`` on Windows when the user's home directory is unavailable.

src/platformdirs/windows.py

@@ -143,7 +143,10 @@ def user_projects_dir(self) -> str:
     @property
     def user_publicshare_dir(self) -> str:
         r"""Public share directory e.g. ``C:\Users\Public``."""
-        return os.path.normpath(os.environ.get("PUBLIC", str(Path("~").expanduser().parent / "Public")))
+        path = os.environ.get("PUBLIC")
+        if path is None:
+            path = str(Path("~").expanduser().parent / "Public")
+        return os.path.normpath(path)
 
     @property
     def user_templates_dir(self) -> str:

tests/test_windows.py

@@ -112,6 +112,18 @@ def test_windows(params: dict[str, Any], func: str) -> None:
     assert result == expected_map[func]
 
 
+def test_publicshare_dir_with_unavailable_home(monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture) -> None:
+    monkeypatch.setenv("PUBLIC", r"C:\Users\Shared")
+    mocker.patch.object(Path, "expanduser", side_effect=RuntimeError("Could not determine home directory."))
+    assert Windows().user_publicshare_dir == os.path.normpath(r"C:\Users\Shared")
+
+
+def test_publicshare_dir_fallback(monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture) -> None:
+    monkeypatch.delenv("PUBLIC", raising=False)
+    mocker.patch.object(Path, "expanduser", return_value=Path("C:/Users/Test"))
+    assert Windows().user_publicshare_dir == os.path.normpath("C:/Users/Public")
+
+
 def test_roaming_uses_appdata(mocker: MockerFixture) -> None:
     mock = mocker.patch("platformdirs.windows.get_win_folder", side_effect=lambda csidl: _WIN_FOLDERS[csidl])
     _result = Windows(appname="foo", roaming=True).user_data_dir