Make VersionControl.make_rev_args() a class method.

src/pip/_internal/vcs/__init__.py

@@ -337,7 +337,8 @@ class VersionControl(object):
         url = urllib_parse.urlunsplit((scheme, netloc, path, query, ''))
         return url, rev, user_pass
 
-    def make_rev_args(self, username, password):
+    @classmethod
+    def make_rev_args(cls, username, password):
         """
         Return the RevOptions "extra arguments" to use in obtain().
         """

src/pip/_internal/vcs/subversion.py

@@ -113,7 +113,8 @@ class Subversion(VersionControl):
             url = 'svn+' + url
         return url, rev, user_pass
 
-    def make_rev_args(self, username, password):
+    @classmethod
+    def make_rev_args(cls, username, password):
         extra_args = []
         if username:
             extra_args += ['--username', username]

tests/unit/test_vcs.py

@@ -340,7 +340,7 @@ def test_git__make_rev_args(username, password, expected):
     """
     Test VersionControl.make_rev_args().
     """
-    actual = Git().make_rev_args(username, password)
+    actual = Git.make_rev_args(username, password)
     assert actual == expected
 
 
@@ -353,7 +353,7 @@ def test_subversion__make_rev_args(username, password, expected):
     """
     Test Subversion.make_rev_args().
     """
-    actual = Subversion().make_rev_args(username, password)
+    actual = Subversion.make_rev_args(username, password)
     assert actual == expected