Accommodate for recent pathname2url() changes upstream

- UNC paths converted to URLs now start with two slashes, like earlier (yes, really)
- Trailing slashes are now preserved on Windows, matching POSIX behaviour

Author: ichard26

news/ba0bd1bb-2dcc-43d0-83ff-c762e7e55bf9.trivial.rst

@@ -29,6 +29,7 @@
     cast,
 )
 from urllib.parse import urlparse, urlunparse
+from urllib.request import pathname2url
 from zipfile import ZipFile
 
 import pytest
@@ -1379,6 +1380,10 @@ def __call__(
 
 CertFactory = Callable[[], str]
 
+# -------------------------------------------------------------------------
+# Accommodations for Windows path and URL changes in recent Python releases
+# -------------------------------------------------------------------------
+
 # versions containing fix/backport from https://github.com/python/cpython/pull/113563
 # which changed the behavior of `urllib.parse.urlun{parse,split}`
 url = "////path/to/file"
@@ -1394,3 +1399,15 @@ def __call__(
     sys.platform != "win32" or has_new_urlun_behavior,
     reason="testing windows behavior for older CPython",
 )
+
+# Trailing slashes are now preserved on Windows, matching POSIX behaviour.
+# BPO: https://github.com/python/cpython/issues/126212
+does_pathname2url_preserve_trailing_slash = pathname2url("C:/foo/").endswith("/")
+skip_needs_new_pathname2url_trailing_slash_behavior_win = pytest.mark.skipif(
+    sys.platform != "win32" or not does_pathname2url_preserve_trailing_slash,
+    reason="testing windows (pathname2url) behavior for newer CPython",
+)
+skip_needs_old_pathname2url_trailing_slash_behavior_win = pytest.mark.skipif(
+    sys.platform != "win32" or does_pathname2url_preserve_trailing_slash,
+    reason="testing windows (pathname2url) behavior for older CPython",
+)

tests/lib/__init__.py

@@ -40,7 +40,9 @@
 from tests.lib import (
     TestData,
     make_test_link_collector,
+    skip_needs_new_pathname2url_trailing_slash_behavior_win,
     skip_needs_new_urlun_behavior_win,
+    skip_needs_old_pathname2url_trailing_slash_behavior_win,
     skip_needs_old_urlun_behavior_win,
 )
 
@@ -390,12 +392,26 @@ def test_clean_url_path_with_local_path(path: str, expected: str) -> None:
         pytest.param(
             "file:///T:/path/with spaces/",
             "file:///T:/path/with%20spaces",
-            marks=skip_needs_old_urlun_behavior_win,
+            marks=[
+                skip_needs_old_urlun_behavior_win,
+                skip_needs_old_pathname2url_trailing_slash_behavior_win,
+            ],
         ),
         pytest.param(
             "file:///T:/path/with spaces/",
             "file://///T:/path/with%20spaces",
-            marks=skip_needs_new_urlun_behavior_win,
+            marks=[
+                skip_needs_new_urlun_behavior_win,
+                skip_needs_old_pathname2url_trailing_slash_behavior_win,
+            ],
+        ),
+        pytest.param(
+            "file:///T:/path/with spaces/",
+            "file://///T:/path/with%20spaces/",
+            marks=[
+                skip_needs_new_urlun_behavior_win,
+                skip_needs_new_pathname2url_trailing_slash_behavior_win,
+            ],
         ),
         # URL with Windows drive letter, running on non-windows
         # platform. The `:` after the drive should be quoted.

tests/unit/test_collector.py

@@ -6,11 +6,6 @@
 
 from pip._internal.utils.urls import path_to_url, url_to_path
 
-from tests.lib import (
-    skip_needs_new_urlun_behavior_win,
-    skip_needs_old_urlun_behavior_win,
-)
-
 
 @pytest.mark.skipif("sys.platform == 'win32'")
 def test_path_to_url_unix() -> None:
@@ -25,23 +20,22 @@ def test_path_to_url_unix() -> None:
     [
         pytest.param("c:/tmp/file", "file:///C:/tmp/file", id="posix-path"),
         pytest.param("c:\\tmp\\file", "file:///C:/tmp/file", id="nt-path"),
-        pytest.param(
-            r"\\unc\as\path",
-            "file://unc/as/path",
-            marks=skip_needs_old_urlun_behavior_win,
-            id="unc-path",
-        ),
-        pytest.param(
-            r"\\unc\as\path",
-            "file:////unc/as/path",
-            marks=skip_needs_new_urlun_behavior_win,
-        ),
     ],
 )
 def test_path_to_url_win(path: str, url: str) -> None:
     assert path_to_url(path) == url
 
 
+@pytest.mark.skipif("sys.platform != 'win32'")
+def test_unc_path_to_url_win() -> None:
+    # The two and four slash forms are both acceptable for our purposes. CPython's
+    # behaviour has changed several times here, so blindly accept either.
+    # - https://github.com/python/cpython/issues/78457
+    # - https://github.com/python/cpython/issues/126205
+    url = path_to_url(r"\\unc\as\path")
+    assert url in ["file://unc/as/path", "file:////unc/as/path"]
+
+
 @pytest.mark.skipif("sys.platform != 'win32'")
 def test_relative_path_to_url_win() -> None:
     resolved_path = os.path.join(os.getcwd(), "file")