Fix cleaning of local URLs with VCS schemes (#13509)

Ensure that the scheme is `"file"` when we call `urlunsplit()`. This
ensures that a URL with an explicit authority section is returned.

Author: barneygale

news/13509.bugfix.rst

@@ -0,0 +1 @@
+Fix normalization of local links with non-``file`` schemes.

src/pip/_internal/models/link.py

@@ -177,7 +177,11 @@ def _ensure_quoted_url(url: str) -> str:
     # If the netloc is empty, then the URL refers to a local filesystem path.
     is_local_path = not result.netloc
     path = _clean_url_path(result.path, is_local_path=is_local_path)
-    return urllib.parse.urlunsplit(result._replace(path=path))
+    # Temporarily replace scheme with file to ensure the URL generated by
+    # urlunsplit() contains an empty netloc (file://) as per RFC 1738.
+    ret = urllib.parse.urlunsplit(result._replace(scheme="file", path=path))
+    ret = result.scheme + ret[4:]  # Restore original scheme.
+    return ret
 
 
 def _absolute_link_url(base_url: str, url: str) -> str:

tests/unit/test_collector.py

@@ -436,7 +436,7 @@ def test_clean_url_path_with_local_path(path: str, expected: str) -> None:
         # running on non-windows platform.
         pytest.param(
             "git+file:///T:/with space/[email protected]#egg=my-package-1.0",
-            "git+file:/T%3A/with%20space/[email protected]#egg=my-package-1.0",
+            "git+file:///T%3A/with%20space/[email protected]#egg=my-package-1.0",
             marks=pytest.mark.skipif("sys.platform == 'win32'"),
         ),
     ],