rebase: write script before initializing state

If rebase.instructionFormat is invalid the repository is left in a
strange state when the interactive rebase fails. `git status` outputs
boths the same as it would in the normal case *and* something related to
interactive rebase:

    $ git -c rebase.instructionFormat=blah rebase -i
    fatal: invalid --pretty format: blah
    $ git status
    On branch master
    Your branch is ahead of 'upstream/master' by 1 commit.
      (use "git push" to publish your local commits)

    git-rebase-todo is missing.
    No commands done.
    No commands remaining.
    You are currently editing a commit while rebasing branch 'master' on '8db3019401'.
      (use "git commit --amend" to amend the current commit)
      (use "git rebase --continue" once you are satisfied with your changes)

By attempting to write the rebase script before initializing the state
this potential scenario is avoided.

Signed-off-by: Junio C Hamano <[email protected]>

Author: Osse

builtin/rebase.c

@@ -292,15 +292,6 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 				&revisions, &shortrevisions))
 		goto cleanup;
 
-	if (init_basic_state(&replay,
-			     opts->head_name ? opts->head_name : "detached HEAD",
-			     opts->onto, &opts->orig_head->object.oid))
-		goto cleanup;
-
-	if (!opts->upstream && opts->squash_onto)
-		write_file(path_squash_onto(), "%s\n",
-			   oid_to_hex(opts->squash_onto));
-
 	strvec_pushl(&make_script_args, "", revisions, NULL);
 	if (opts->restrict_revision)
 		strvec_pushf(&make_script_args, "^%s",
@@ -309,21 +300,30 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 	ret = sequencer_make_script(the_repository, &todo_list.buf,
 				    make_script_args.nr, make_script_args.v,
 				    flags);
-
-	if (ret)
+	if (ret) {
 		error(_("could not generate todo list"));
-	else {
-		discard_index(the_repository->index);
-		if (todo_list_parse_insn_buffer(the_repository, &replay,
-						todo_list.buf.buf, &todo_list))
-			BUG("unusable todo list");
-
-		ret = complete_action(the_repository, &replay, flags,
-			shortrevisions, opts->onto_name, opts->onto,
-			&opts->orig_head->object.oid, &opts->exec,
-			opts->autosquash, opts->update_refs, &todo_list);
+		goto cleanup;
 	}
 
+	if (init_basic_state(&replay,
+			     opts->head_name ? opts->head_name : "detached HEAD",
+			     opts->onto, &opts->orig_head->object.oid))
+		goto cleanup;
+
+	if (!opts->upstream && opts->squash_onto)
+		write_file(path_squash_onto(), "%s\n",
+			   oid_to_hex(opts->squash_onto));
+
+	discard_index(the_repository->index);
+	if (todo_list_parse_insn_buffer(the_repository, &replay,
+					todo_list.buf.buf, &todo_list))
+		BUG("unusable todo list");
+
+	ret = complete_action(the_repository, &replay, flags,
+		shortrevisions, opts->onto_name, opts->onto,
+		&opts->orig_head->object.oid, &opts->exec,
+		opts->autosquash, opts->update_refs, &todo_list);
+
 cleanup:
 	replay_opts_release(&replay);
 	free(revisions);

t/t3415-rebase-autosquash.sh

@@ -394,6 +394,16 @@ test_expect_success 'autosquash with empty custom instructionFormat' '
 	)
 '
 
+test_expect_success 'autosquash with invalid custom instructionFormat' '
+	git reset --hard base &&
+	test_commit invalid-instructionFormat-test &&
+	(
+		test_must_fail git -c rebase.instructionFormat=blah \
+			rebase --autosquash  --force-rebase -i HEAD^ &&
+		test_path_is_missing .git/rebase-merge
+	)
+'
+
 set_backup_editor () {
 	write_script backup-editor.sh <<-\EOF
 	cp "$1" .git/backup-"$(basename "$1")"