rebase -i: rewrite checkout_onto() in C

This rewrites checkout_onto() from shell to C.

A new command (“checkout-onto”) is added to rebase--helper.c. The shell
version is then stripped.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase--helper.c

@@ -18,7 +18,8 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 	enum {
 		CONTINUE = 1, ABORT, MAKE_SCRIPT, SHORTEN_OIDS, EXPAND_OIDS,
 		CHECK_TODO_LIST, SKIP_UNNECESSARY_PICKS, REARRANGE_SQUASH,
-		ADD_EXEC, APPEND_TODO_HELP, EDIT_TODO, PREPARE_BRANCH
+		ADD_EXEC, APPEND_TODO_HELP, EDIT_TODO, PREPARE_BRANCH,
+		CHECKOUT_ONTO
 	} command = 0;
 	struct option options[] = {
 		OPT_BOOL(0, "ff", &opts.allow_ff, N_("allow fast-forward")),
@@ -54,6 +55,8 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 			    EDIT_TODO),
 		OPT_CMDMODE(0, "prepare-branch", &command,
 			    N_("prepare the branch to be rebased"), PREPARE_BRANCH),
+		OPT_CMDMODE(0, "checkout-onto", &command,
+			    N_("checkout a commit"), CHECKOUT_ONTO),
 		OPT_END()
 	};
 
@@ -99,5 +102,7 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 		return !!edit_todo_list(flags);
 	if (command == PREPARE_BRANCH && argc == 2)
 		return !!prepare_branch_to_be_rebased(&opts, argv[1]);
+	if (command == CHECKOUT_ONTO && argc == 4)
+		return !!checkout_onto(&opts, argv[1], argv[2], argv[3]);
 	usage_with_options(builtin_rebase_helper_usage, options);
 }

git-rebase--interactive.sh

@@ -28,17 +28,6 @@ case "$comment_char" in
 	;;
 esac
 
-orig_reflog_action="$GIT_REFLOG_ACTION"
-
-comment_for_reflog () {
-	case "$orig_reflog_action" in
-	''|rebase*)
-		GIT_REFLOG_ACTION="rebase -i ($1)"
-		export GIT_REFLOG_ACTION
-		;;
-	esac
-}
-
 die_abort () {
 	apply_autostash
 	rm -rf "$state_dir"
@@ -70,14 +59,6 @@ collapse_todo_ids() {
 	git rebase--helper --shorten-ids
 }
 
-# Switch to the branch in $into and notify it in the reflog
-checkout_onto () {
-	comment_for_reflog start
-	GIT_REFLOG_ACTION="$GIT_REFLOG_ACTION: checkout $onto_name"
-	output git checkout $onto || die_abort "$(gettext "could not detach HEAD")"
-	git update-ref ORIG_HEAD $orig_head
-}
-
 get_missing_commit_check_level () {
 	check_level=$(git config --get rebase.missingCommitsCheck)
 	check_level=${check_level:-ignore}
@@ -176,7 +157,8 @@ EOF
 
 	git rebase--helper --check-todo-list || {
 		ret=$?
-		checkout_onto
+		git rebase--helper --checkout-onto "$onto_name" "$onto" \
+		    "$orig_head" ${verbose:+--verbose}
 		exit $ret
 	}
 
@@ -186,7 +168,8 @@ EOF
 	onto="$(git rebase--helper --skip-unnecessary-picks)" ||
 	die "Could not skip unnecessary pick commands"
 
-	checkout_onto
+	git rebase--helper --checkout-onto "$onto_name" "$onto" "$orig_head" \
+	    ${verbose:+--verbose}
 	require_clean_work_tree "rebase"
 	exec git rebase--helper ${force_rebase:+--no-ff} $allow_empty_message \
 	     --continue

sequencer.c

@@ -3169,6 +3169,25 @@ int prepare_branch_to_be_rebased(struct replay_opts *opts, const char *commit)
 	return 0;
 }
 
+int checkout_onto(struct replay_opts *opts,
+		  const char *onto_name, const char *onto,
+		  const char *orig_head)
+{
+	struct object_id oid;
+	const char *action = reflog_message(opts, "start", "checkout %s", onto_name);
+
+	if (get_oid(orig_head, &oid))
+		return error(_("%s: not a valid OID"), orig_head);
+
+	if (run_git_checkout(opts, onto, action)) {
+		apply_autostash(opts);
+		sequencer_remove_state(opts);
+		return error(_("could not detach HEAD"));
+	}
+
+	return update_ref(NULL, "ORIG_HEAD", &oid, NULL, 0, UPDATE_REFS_MSG_ON_ERR);
+}
+
 static const char rescheduled_advice[] =
 N_("Could not execute the todo command\n"
 "\n"

sequencer.h

@@ -110,6 +110,9 @@ void commit_post_rewrite(const struct commit *current_head,
 			 const struct object_id *new_head);
 
 int prepare_branch_to_be_rebased(struct replay_opts *opts, const char *commit);
+int checkout_onto(struct replay_opts *opts,
+		  const char *onto_name, const char *onto,
+		  const char *orig_head);
 
 #define SUMMARY_INITIAL_COMMIT   (1 << 0)
 #define SUMMARY_SHOW_AUTHOR_DATE (1 << 1)