Use commit encoding for trailer parsing

Agent-Logs-Url: https://github.com/gitpython-developers/GitPython/sessions/519084d5-d5e2-4486-a9cc-5c258e596e13

Co-authored-by: Byron <63622+Byron@users.noreply.github.com>

Author: Copilot

git/objects/commit.py

@@ -450,7 +450,7 @@ def trailers_list(self) -> List[Tuple[str, str]]:
         :return:
             List containing key-value tuples of whitespace stripped trailer information.
         """
-        trailer = self._interpret_trailers(self.repo, self.message, ["--parse"]).strip()
+        trailer = self._interpret_trailers(self.repo, self.message, ["--parse"], encoding=self.encoding).strip()
 
         if not trailer:
             return []
@@ -463,17 +463,23 @@ def trailers_list(self) -> List[Tuple[str, str]]:
         return trailer_list
 
     @classmethod
-    def _interpret_trailers(cls, repo: "Repo", message: Union[str, bytes], trailer_args: Sequence[str]) -> str:
+    def _interpret_trailers(
+        cls,
+        repo: "Repo",
+        message: Union[str, bytes],
+        trailer_args: Sequence[str],
+        encoding: str = default_encoding,
+    ) -> str:
         cmd = [repo.git.GIT_PYTHON_GIT_EXECUTABLE, "interpret-trailers", *trailer_args]
         proc: Git.AutoInterrupt = repo.git.execute(  # type: ignore[call-overload]
             cmd,
             as_process=True,
             istream=PIPE,
         )
-        message_bytes = message if isinstance(message, bytes) else message.encode(cls.default_encoding, errors="strict")
+        message_bytes = message if isinstance(message, bytes) else message.encode(encoding, errors="strict")
         stdout_bytes, _ = proc.communicate(message_bytes)
         finalize_process(proc)
-        return stdout_bytes.decode(cls.default_encoding, errors="strict")
+        return stdout_bytes.decode(encoding, errors="strict")
 
     @property
     def trailers_dict(self) -> Dict[str, List[str]]:

test/test_commit.py

@@ -647,6 +647,30 @@ def test_create_from_tree_with_non_utf8_trailers(self, rw_dir):
         assert "Reviewed-by: André <andre@example.com>" in commit.message
         assert commit.trailers_list == [("Reviewed-by", "André <andre@example.com>")]
 
+    @with_rw_directory
+    def test_trailers_list_with_non_utf8_message_bytes(self, rw_dir):
+        """Test that trailer parsing handles non-UTF-8 commit message bytes."""
+        rw_repo = Repo.init(osp.join(rw_dir, "test_trailers_non_utf8_bytes"))
+        with rw_repo.config_writer() as writer:
+            writer.set_value("i18n", "commitencoding", "ISO-8859-1")
+
+        path = osp.join(str(rw_repo.working_tree_dir), "hello.txt")
+        touch(path)
+        rw_repo.index.add([path])
+        tree = rw_repo.index.write_tree()
+
+        commit = Commit.create_from_tree(
+            rw_repo,
+            tree,
+            "Résumé",
+            head=True,
+            trailers={"Reviewed-by": "André <andre@example.com>"},
+        )
+
+        commit.message = commit.message.encode(commit.encoding)
+
+        assert commit.trailers_list == [("Reviewed-by", "André <andre@example.com>")]
+
     @with_rw_directory
     def test_index_commit_with_trailers(self, rw_dir):
         """Test that IndexFile.commit() supports adding trailers."""