Unquote path before testing for '@'

The url can be quoted so the '@' will be %20 and it will not be split as
revision number.

news/6441.bugfix

@@ -0,0 +1 @@
+Unquote VCS path before testing for '@'

src/pip/_internal/vcs/__init__.py

@@ -339,6 +339,7 @@ def get_url_rev_and_auth(cls, url):
         scheme = scheme.split('+', 1)[1]
         netloc, user_pass = cls.get_netloc_and_auth(netloc, scheme)
         rev = None
+        path = urllib_parse.unquote(path)
         if '@' in path:
             path, rev = path.rsplit('@', 1)
         url = urllib_parse.urlunsplit((scheme, netloc, path, query, ''))

tests/unit/test_vcs.py

@@ -258,6 +258,11 @@ def test_git__get_url_rev__idempotent():
     # Test a "+" in the path portion.
     ('svn+https://svn.example.com/My+Project',
      ('https://svn.example.com/My+Project', None, (None, None))),
+    ('hg+https://hg.example.com/MyProject@default',
+     ('https://hg.example.com/MyProject', 'default', (None, None))),
+    # Test with "@" quoted.
+    ('hg+https://hg.example.com/MyProject%40default',
+     ('https://hg.example.com/MyProject', 'default', (None, None))),
 ])
 def test_version_control__get_url_rev_and_auth(url, expected):
     """