Add reverting reflog move if an error happens.

src/libgit2/refdb_fs.c

@@ -1779,17 +1779,20 @@ static int refdb_fs_backend__rename(
 	}
 
 	if ((error = refdb_fs_backend__delete(_backend, old_name, NULL, NULL)) < 0) {
+		refdb_reflog_fs__rename(_backend, new_name, old_name);
 		git_reference_free(old);
 		return error;
 	}
 
 	new = git_reference__realloc(&old, new_name);
 	if (!new) {
+		refdb_reflog_fs__rename(_backend, new_name, old_name);
 		git_reference_free(old);
 		return -1;
 	}
 
 	if ((error = loose_lock(&file, backend, new->name)) < 0) {
+		refdb_reflog_fs__rename(_backend, new_name, old_name);
 		git_reference_free(new);
 		return error;
 	}

tests/libgit2/refs/branches/move.c

@@ -232,3 +232,19 @@ void test_refs_branches_move__moves_reflog_correctly(void)
     git_reflog_free(original_reflog);
     git_reflog_free(new_reflog);
 }
+
+void test_refs_branches_move__failed_move_restores_reflog(void)
+{
+	git_reference *original_ref, *new_ref;
+	git_reflog *recovered_reflog;
+
+	cl_git_pass(git_reference_lookup(&original_ref, repo, "refs/heads/br2"));
+
+	cl_assert_equal_i(GIT_EINVALIDSPEC, git_branch_move(&new_ref, original_ref, "Inv@{id", 0));
+
+	cl_git_pass(git_reflog_read(&recovered_reflog, repo, "refs/heads/br2"));
+	cl_assert_equal_i(2, git_reflog_entrycount(recovered_reflog));
+
+	git_reference_free(original_ref);
+	git_reflog_free(recovered_reflog);
+}