Expose remote branch ref as an environment variable

pre_commit/commands/hook_impl.py

@@ -69,6 +69,7 @@ def _ns(
         color: bool,
         *,
         all_files: bool = False,
+        remote_branch: Optional[str] = None,
         from_ref: Optional[str] = None,
         to_ref: Optional[str] = None,
         remote_name: Optional[str] = None,
@@ -79,6 +80,7 @@ def _ns(
     return argparse.Namespace(
         color=color,
         hook_stage=hook_type.replace('pre-', ''),
+        remote_branch=remote_branch,
         from_ref=from_ref,
         to_ref=to_ref,
         remote_name=remote_name,
@@ -106,13 +108,14 @@ def _pre_push_ns(
     remote_url = args[1]
 
     for line in stdin.decode().splitlines():
-        _, local_sha, _, remote_sha = line.split()
+        _, local_sha, remote_branch, remote_sha = line.split()
         if local_sha == Z40:
             continue
         elif remote_sha != Z40 and _rev_exists(remote_sha):
             return _ns(
                 'pre-push', color,
                 from_ref=remote_sha, to_ref=local_sha,
+                remote_branch=remote_branch,
                 remote_name=remote_name, remote_url=remote_url,
             )
         else:
@@ -133,6 +136,7 @@ def _pre_push_ns(
                         'pre-push', color,
                         all_files=True,
                         remote_name=remote_name, remote_url=remote_url,
+                        remote_branch=remote_branch,
                     )
                 else:
                     rev_cmd = ('git', 'rev-parse', f'{first_ancestor}^')
@@ -141,6 +145,7 @@ def _pre_push_ns(
                         'pre-push', color,
                         from_ref=source, to_ref=local_sha,
                         remote_name=remote_name, remote_url=remote_url,
+                        remote_branch=remote_branch,
                     )
 
     # nothing to push

pre_commit/commands/run.py

@@ -371,7 +371,8 @@ def run(
         environ['PRE_COMMIT_FROM_REF'] = args.from_ref
         environ['PRE_COMMIT_TO_REF'] = args.to_ref
 
-    if args.remote_name and args.remote_url:
+    if args.remote_name and args.remote_url and args.remote_branch:
+        environ['PRE_COMMIT_REMOTE_BRANCH'] = args.remote_branch
         environ['PRE_COMMIT_REMOTE_NAME'] = args.remote_name
         environ['PRE_COMMIT_REMOTE_URL'] = args.remote_url
 

pre_commit/main.py

@@ -96,6 +96,9 @@ def _add_run_options(parser: argparse.ArgumentParser) -> None:
         '--hook-stage', choices=C.STAGES, default='commit',
         help='The stage during which the hook is fired.  One of %(choices)s',
     )
+    parser.add_argument(
+        '--remote-branch', help='Remote branch ref used by `git push`.',
+    )
     parser.add_argument(
         '--from-ref', '--source', '-s',
         help=(

testing/util.py

@@ -61,6 +61,7 @@ def run_opts(
         color=False,
         verbose=False,
         hook=None,
+        remote_branch='',
         from_ref='',
         to_ref='',
         remote_name='',
@@ -78,6 +79,7 @@ def run_opts(
         color=color,
         verbose=verbose,
         hook=hook,
+        remote_branch=remote_branch,
         from_ref=from_ref,
         to_ref=to_ref,
         remote_name=remote_name,

tests/commands/run_test.py

@@ -486,6 +486,7 @@ def test_from_ref_to_ref_error_msg_error(
 def test_all_push_options_ok(cap_out, store, repo_with_passing_hook):
     args = run_opts(
         from_ref='master', to_ref='master',
+        remote_branch='master',
         remote_name='origin', remote_url='https://example.com/repo',
     )
     ret, printed = _do_run(cap_out, store, repo_with_passing_hook, args)