Backport of https://github.com/pypa/pip/pull/9827 with parts of

https://github.com/pypa/pip/pull/4690 to make it work with pip v9.0.1

diff --git a/pip/vcs/git.py b/pip/vcs/git.py

index 2187dd8..d1502f8 100644

--- a/pip/vcs/git.py

+++ b/pip/vcs/git.py

@@ -81,7 +81,7 @@ class Git(VersionControl):

         and branches may need origin/ as a prefix.

         Returns the SHA1 of the branch or tag if found.

         """

-        revisions = self.get_short_refs(dest)

+        revisions = self.get_short_refs(dest, rev)

         origin_rev = 'origin/%s' % rev

         if origin_rev in revisions:

@@ -171,12 +171,20 @@ class Git(VersionControl):

             ['rev-parse', 'HEAD'], show_stdout=False, cwd=location)

         return current_rev.strip()

-    def get_full_refs(self, location):

+    def get_full_refs(self, location, pattern=''):

         """Yields tuples of (commit, ref) for branches and tags"""

-        output = self.run_command(['show-ref'],

+        output = self.run_command(['show-ref', pattern],

                                   show_stdout=False, cwd=location)

-        for line in output.strip().splitlines():

-            commit, ref = line.split(' ', 1)

+        for line in output.split("\n"):

+            line = line.rstrip("\r")

+            if not line:

+                continue

+            try:

+                commit, ref = line.split(' ', 1)

+            except ValueError:

+                # Include the offending line to simplify troubleshooting if

+                # this error ever occurs.

+                raise ValueError(f'unexpected show-ref line: {line!r}')

             yield commit.strip(), ref.strip()

     def is_ref_remote(self, ref):

@@ -200,10 +208,10 @@ class Git(VersionControl):

     def get_refs(self, location):

         return self.get_short_refs(location)

-    def get_short_refs(self, location):

+    def get_short_refs(self, location, pattern=''):

         """Return map of named refs (branches or tags) to commit hashes."""

         rv = {}

-        for commit, ref in self.get_full_refs(location):

+        for commit, ref in self.get_full_refs(location, pattern):

             ref_name = None

             if self.is_ref_remote(ref):

                 ref_name = ref[len('refs/remotes/'):]