reset: introduce ability to skip updating HEAD

In a subsequent commit we'll introduce a new caller to
`reset_working_tree()` that really only wants to update the index and
working tree, without updating any references. Introduce a new flag that
makes the caller opt in to updating HEAD and adapt all callers to set
that flag.

Note that in a previous iteration we instead introduced a flag that made
callers opt out of updating any references. This was somewhat awkward
though because we already have the `UPDATE_ORIG_HEAD` flag, so the
result was somewhat inconsistent.

Suggested-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -607,7 +607,8 @@ static int move_to_original_branch(struct rebase_options *opts)
 	strbuf_addf(&head_reflog, "%s (finish): returning to %s",
 		    opts->reflog_action, opts->head_name);
 	ropts.branch = opts->head_name;
-	ropts.flags = RESET_WORKING_TREE_REFS_ONLY;
+	ropts.flags = RESET_WORKING_TREE_REFS_ONLY |
+		      RESET_WORKING_TREE_UPDATE_HEAD;
 	ropts.branch_msg = branch_reflog.buf;
 	ropts.head_msg = head_reflog.buf;
 	ret = reset_working_tree(the_repository, &ropts);
@@ -693,6 +694,7 @@ static int run_am(struct rebase_options *opts)
 		ropts.oid = &opts->orig_head->object.oid;
 		ropts.branch = opts->head_name;
 		ropts.default_reflog_action = opts->reflog_action;
+		ropts.flags = RESET_WORKING_TREE_UPDATE_HEAD;
 		reset_working_tree(the_repository, &ropts);
 		error(_("\ngit encountered an error while preparing the "
 			"patches to replay\n"
@@ -862,7 +864,8 @@ static int checkout_up_to_date(struct rebase_options *options)
 		    options->reflog_action, options->switch_to);
 	ropts.oid = &options->orig_head->object.oid;
 	ropts.branch = options->head_name;
-	ropts.flags = RESET_WORKING_TREE_RUN_POST_CHECKOUT_HOOK;
+	ropts.flags = RESET_WORKING_TREE_RUN_POST_CHECKOUT_HOOK |
+		      RESET_WORKING_TREE_UPDATE_HEAD;
 	if (!ropts.branch)
 		ropts.flags |=  RESET_WORKING_TREE_DETACH;
 	ropts.head_msg = buf.buf;
@@ -1384,7 +1387,8 @@ int cmd_rebase(int argc,
 
 		rerere_clear(the_repository, &merge_rr);
 		string_list_clear(&merge_rr, 1);
-		ropts.flags = RESET_WORKING_TREE_HARD;
+		ropts.flags = RESET_WORKING_TREE_HARD |
+			      RESET_WORKING_TREE_UPDATE_HEAD;
 		if (reset_working_tree(the_repository, &ropts) < 0)
 			die(_("could not discard worktree changes"));
 		remove_branch_state(the_repository, 0);
@@ -1409,7 +1413,8 @@ int cmd_rebase(int argc,
 		ropts.oid = &options.orig_head->object.oid;
 		ropts.head_msg = head_msg.buf;
 		ropts.branch = options.head_name;
-		ropts.flags = RESET_WORKING_TREE_HARD;
+		ropts.flags = RESET_WORKING_TREE_HARD |
+			      RESET_WORKING_TREE_UPDATE_HEAD;
 		if (reset_working_tree(the_repository, &ropts) < 0)
 			die(_("could not move back to %s"),
 			    oid_to_hex(&options.orig_head->object.oid));
@@ -1877,6 +1882,7 @@ int cmd_rebase(int argc,
 	ropts.oid = &options.onto->object.oid;
 	ropts.orig_head = &options.orig_head->object.oid;
 	ropts.flags = RESET_WORKING_TREE_DETACH |
+		      RESET_WORKING_TREE_UPDATE_HEAD |
 		      RESET_WORKING_TREE_UPDATE_ORIG_HEAD |
 		      RESET_WORKING_TREE_RUN_POST_CHECKOUT_HOOK;
 	ropts.head_msg = msg.buf;

reset.c

@@ -92,6 +92,7 @@ int reset_working_tree(struct repository *r,
 	const char *switch_to_branch = opts->branch;
 	unsigned reset_hard = opts->flags & RESET_WORKING_TREE_HARD;
 	unsigned refs_only = opts->flags & RESET_WORKING_TREE_REFS_ONLY;
+	unsigned update_head = opts->flags & RESET_WORKING_TREE_UPDATE_HEAD;
 	unsigned update_orig_head = opts->flags & RESET_WORKING_TREE_UPDATE_ORIG_HEAD;
 	unsigned dry_run = opts->flags & RESET_WORKING_TREE_DRY_RUN;
 	struct object_id *head = NULL, head_oid;
@@ -113,6 +114,9 @@ int reset_working_tree(struct repository *r,
 	if (opts->branch_msg && !opts->branch)
 		BUG("branch reflog message given without a branch");
 
+	if (update_orig_head && !update_head)
+		BUG("cannot update ORIG_HEAD without updating HEAD" );
+
 	if (!refs_only && !dry_run && repo_hold_locked_index(r, &lock, LOCK_REPORT_ON_ERROR) < 0) {
 		ret = -1;
 		goto leave_reset_head;
@@ -129,7 +133,7 @@ int reset_working_tree(struct repository *r,
 		oid = &head_oid;
 
 	if (refs_only) {
-		if (!dry_run)
+		if (!dry_run && update_head)
 			return update_refs(r, opts, oid, head);
 		return 0;
 	}
@@ -197,7 +201,8 @@ int reset_working_tree(struct repository *r,
 		goto leave_reset_head;
 	}
 
-	if (oid != &head_oid || update_orig_head || switch_to_branch)
+	if (update_head &&
+	    (oid != &head_oid || update_orig_head || switch_to_branch))
 		ret = update_refs(r, opts, oid, head);
 
 leave_reset_head:

reset.h

@@ -19,14 +19,17 @@ enum reset_working_tree_flags {
 	/* Only update refs, do not touch the worktree */
 	RESET_WORKING_TREE_REFS_ONLY = (1 << 3),
 
-	/* Update ORIG_HEAD as well as HEAD */
-	RESET_WORKING_TREE_UPDATE_ORIG_HEAD = (1 << 4),
+	/* Update HEAD */
+	RESET_WORKING_TREE_UPDATE_HEAD = (1 << 4),
+
+	/* Update ORIG_HEAD */
+	RESET_WORKING_TREE_UPDATE_ORIG_HEAD = (1 << 5),
 
 	/*
 	 * Perform a dry-run by performing the operation without updating
 	 * any user-visible state.
 	 */
-	RESET_WORKING_TREE_DRY_RUN = (1 << 5),
+	RESET_WORKING_TREE_DRY_RUN = (1 << 6),
 };
 
 struct reset_working_tree_options {

sequencer.c

@@ -4678,7 +4678,8 @@ static void create_autostash_internal(struct repository *r,
 	    has_uncommitted_changes(r, 1)) {
 		struct child_process stash = CHILD_PROCESS_INIT;
 		struct reset_working_tree_options ropts = {
-			.flags = RESET_WORKING_TREE_HARD,
+			.flags = RESET_WORKING_TREE_HARD |
+				 RESET_WORKING_TREE_UPDATE_HEAD,
 		};
 		struct object_id oid;
 
@@ -4873,6 +4874,7 @@ static int checkout_onto(struct repository *r, struct replay_opts *opts,
 		.oid = onto,
 		.orig_head = orig_head,
 		.flags = RESET_WORKING_TREE_DETACH |
+			 RESET_WORKING_TREE_UPDATE_HEAD |
 			 RESET_WORKING_TREE_UPDATE_ORIG_HEAD |
 			 RESET_WORKING_TREE_RUN_POST_CHECKOUT_HOOK,
 		.head_msg = reflog_message(opts, "start", "checkout %s",