Fix UNC bug in _win32_longpath (#34)

Fixes #33

CHANGELOG.rst

@@ -1,8 +1,14 @@
 pytest-datadir
 ==============
 
+UNRELEASED
+----------
+
+- Fix handling of UNC paths on Windows (`#33 <https://github.com/gabrielcnr/pytest-datadir/issues/33>`__).
+
 1.4.1 (2022-10-24)
 ------------------
+
 - Replace usage of ``tmpdir`` by ``tmp_path`` (`#48 <https://github.com/gabrielcnr/pytest-datadir/pull/48>`__).
 
 

src/pytest_datadir/plugin.py

@@ -16,7 +16,17 @@ def _win32_longpath(path):
         # to a path string tells the Windows APIs to disable all string parsing
         # and to send the string that follows it straight to the file system".
         # (See https://docs.microsoft.com/pt-br/windows/desktop/FileIO/naming-a-file)
-        return "\\\\?\\" + os.path.normpath(path)
+        normalized = os.path.normpath(path)
+        if not normalized.startswith("\\\\?\\"):
+            is_unc = normalized.startswith("\\\\")
+            # see https://en.wikipedia.org/wiki/Path_(computing)#Universal_Naming_Convention # noqa: E501
+            if (
+                is_unc
+            ):  # then we need to insert an additional "UNC\" to the longpath prefix
+                normalized = normalized.replace("\\\\", "\\\\?\\UNC\\")
+            else:
+                normalized = "\\\\?\\" + normalized
+        return normalized
     else:
         return path
 

tests/test_pathlib.py

@@ -0,0 +1,20 @@
+import sys
+
+import pytest
+from pytest_datadir.plugin import _win32_longpath
+
+
+def test_win32_longpath_idempotent(datadir):
+    """Double application should not prepend twice."""
+    first = _win32_longpath(str(datadir))
+    second = _win32_longpath(first)
+    assert first == second
+
+
+@pytest.mark.skipif(
+    not sys.platform.startswith("win"), reason="Only makes sense on Windows"
+)
+def test_win32_longpath_unc(datadir):
+    unc_path = r"\\ComputerName\SharedFolder\Resource"
+    longpath = _win32_longpath(unc_path)
+    assert longpath.startswith("\\\\?\\UNC\\")