Fix PushToHubMixin when pusing to a PR revision (#34090)

src/transformers/utils/hub.py

@@ -802,7 +802,7 @@ class PushToHubMixin:
                     CommitOperationAdd(path_or_fileobj=os.path.join(working_dir, file), path_in_repo=file)
                 )
 
-        if revision is not None:
+        if revision is not None and not revision.startswith("refs/pr"):
             try:
                 create_branch(repo_id=repo_id, branch=revision, token=token, exist_ok=True)
             except HfHubHTTPError as e:

tests/generation/test_configuration_utils.py

@@ -20,7 +20,7 @@ import unittest
 import warnings
 from pathlib import Path
 
-from huggingface_hub import HfFolder, delete_repo
+from huggingface_hub import HfFolder, create_pull_request, create_repo, delete_repo
 from parameterized import parameterized
 
 from transformers import AutoConfig, GenerationConfig, WatermarkingConfig, is_torch_available
@@ -764,3 +764,29 @@ class ConfigPushToHubTester(unittest.TestCase):
             finally:
                 # Always (try to) delete the repo.
                 self._try_delete_repo(repo_id=tmp_repo, token=self._token)
+
+    def test_push_to_hub_on_pr_revision(self):
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            try:
+                # create a repo and a PR
+                repo_id = f"{USER}/test-generation-config-{Path(tmp_dir).name}"
+                create_repo(repo_id=repo_id, token=self._token)
+                pr = create_pull_request(repo_id=repo_id, title="Test PR", token=self._token)
+                revision = f"refs/pr/{pr.num}"
+
+                # push to PR ref
+                config = GenerationConfig(
+                    do_sample=True,
+                    temperature=0.7,
+                    length_penalty=1.0,
+                )
+                config.push_to_hub(repo_id, token=self._token, revision=revision)
+
+                # load from PR ref
+                new_config = GenerationConfig.from_pretrained(repo_id, revision=revision)
+                for k, v in config.to_dict().items():
+                    if k != "transformers_version":
+                        self.assertEqual(v, getattr(new_config, k))
+            finally:
+                # Always (try to) delete the repo.
+                self._try_delete_repo(repo_id=repo_id, token=self._token)