[PATCH 4/5] rebase -i: don't fork git checkout

["Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com>]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

The "apply" based rebase has avoided forking git checkout since
ac7f467fef ("builtin/rebase: support running "git rebase <upstream>"",
2018-08-07). The code that handles the checkout was moved into libgit
by b309a97108 ("reset: extract reset_head() from rebase", 2020-04-07)
so lets start using it for the "merge" based rebase as well. This
opens the way for us to stop calling the post-checkout hook in the
future.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 sequencer.c | 29 ++++-------------------------
 1 file changed, 4 insertions(+), 25 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index d51440ddcd9..1a9dbc70d3c 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4192,42 +4192,21 @@ int apply_autostash_oid(const char *stash_oid)
 	return apply_save_autostash_oid(stash_oid, 1);
 }
 
-static int run_git_checkout(struct repository *r, struct replay_opts *opts,
-			    const char *commit, const char *action)
-{
-	struct child_process cmd = CHILD_PROCESS_INIT;
-	int ret;
-
-	cmd.git_cmd = 1;
-
-	strvec_push(&cmd.args, "checkout");
-	strvec_push(&cmd.args, commit);
-	strvec_pushf(&cmd.env_array, GIT_REFLOG_ACTION "=%s", action);
-
-	if (opts->verbose)
-		ret = run_command(&cmd);
-	else
-		ret = run_command_silent_on_success(&cmd);
-
-	if (!ret)
-		discard_index(r->index);
-
-	return ret;
-}
-
 static int checkout_onto(struct repository *r, struct replay_opts *opts,
 			 const char *onto_name, const struct object_id *onto,
 			 const struct object_id *orig_head)
 {
 	const char *action = reflog_message(opts, "start", "checkout %s", onto_name);
 
-	if (run_git_checkout(r, opts, oid_to_hex(onto), action)) {
+	if (reset_head(r, onto, "checkout", NULL, RESET_HEAD_DETACH |
+		       RESET_ORIG_HEAD | RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
+		       NULL, action, "rebase")) {
 		apply_autostash(rebase_path_autostash());
 		sequencer_remove_state(opts);
 		return error(_("could not detach HEAD"));
 	}
 
-	return update_ref(NULL, "ORIG_HEAD", orig_head, NULL, 0, UPDATE_REFS_MSG_ON_ERR);
+	return 0;
 }
 
 static int stopped_at_head(struct repository *r)
-- 
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