reset_head(): make default_reflog_action optional

This parameter is only needed when a ref is going to be updated and
the caller does not pass an explicit reflog message. Callers that are
only discarding uncommitted changes in the working tree such as such
as "rebase --skip" or create_autostash() do not update any refs so
should not have to worry about passing this parameter.

This change is not intended to have any user visible changes. The
pointer comparison between `oid` and `&head_oid` checks that the
caller did not pass an oid to be checked out. As no callers pass
RESET_HEAD_RUN_POST_CHECKOUT_HOOK without passing an oid there are
no changes to when the post-checkout hook is run. As update_ref() only
updates the ref if the oid passed to it differs from the current ref
there are no changes to when HEAD is updated.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 16 insertions, 10 deletions

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 2e5a535..82be965 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -585,8 +585,7 @@ static int move_to_original_branch(struct rebase_options *opts)
 		    opts->head_name);
 	ret = reset_head(the_repository, NULL, opts->head_name,
 			 RESET_HEAD_REFS_ONLY,
-			 orig_head_reflog.buf, head_reflog.buf,
-			 DEFAULT_REFLOG_ACTION);
+			 orig_head_reflog.buf, head_reflog.buf, NULL);
 
 	strbuf_release(&orig_head_reflog);
 	strbuf_release(&head_reflog);
@@ -822,7 +821,7 @@ static int checkout_up_to_date(struct rebase_options *options)
 		    options->switch_to);
 	if (reset_head(the_repository, &options->orig_head,
 		       options->head_name, RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
-		       NULL, buf.buf, DEFAULT_REFLOG_ACTION) < 0)
+		       NULL, buf.buf, NULL) < 0)
 		ret = error(_("could not switch to %s"), options->switch_to);
 	strbuf_release(&buf);
 
@@ -1273,7 +1272,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		string_list_clear(&merge_rr, 1);
 
 		if (reset_head(the_repository, NULL, NULL, RESET_HEAD_HARD,
-			       NULL, NULL, DEFAULT_REFLOG_ACTION) < 0)
+			       NULL, NULL, NULL) < 0)
 			die(_("could not discard worktree changes"));
 		remove_branch_state(the_repository, 0);
 		if (read_basic_state(&options))
@@ -1778,8 +1777,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			options.head_name ? options.head_name : "detached HEAD",
 			oid_to_hex(&options.onto->object.oid));
 		reset_head(the_repository, NULL, options.head_name,
-			   RESET_HEAD_REFS_ONLY, "HEAD", msg.buf,
-			   DEFAULT_REFLOG_ACTION);
+			   RESET_HEAD_REFS_ONLY, "HEAD", msg.buf, NULL);
 		strbuf_release(&msg);
 		ret = finish_rebase(&options);
 		goto cleanup;
diff --git a/reset.c b/reset.c
index 56d6e2a..4a92e4b 100644
--- a/reset.c
+++ b/reset.c
@@ -22,8 +22,13 @@ static int update_refs(const struct object_id *oid, const char *switch_to_branch
 	size_t prefix_len;
 	int ret;
 
-	reflog_action = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
-	strbuf_addf(&msg, "%s: ", reflog_action ? reflog_action : default_reflog_action);
+	if ((update_orig_head && !reflog_orig_head) || !reflog_head) {
+		if (!default_reflog_action)
+			BUG("default_reflog_action must be given when reflog messages are omitted");
+		reflog_action = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
+		strbuf_addf(&msg, "%s: ", reflog_action ? reflog_action :
+							  default_reflog_action);
+	}
 	prefix_len = msg.len;
 
 	if (update_orig_head) {
@@ -71,6 +76,7 @@ int reset_head(struct repository *r, struct object_id *oid,
 {
 	unsigned reset_hard = flags & RESET_HEAD_HARD;
 	unsigned refs_only = flags & RESET_HEAD_REFS_ONLY;
+	unsigned update_orig_head = flags & RESET_ORIG_HEAD;
 	struct object_id *head = NULL, head_oid;
 	struct tree_desc desc[2] = { { NULL }, { NULL } };
 	struct lock_file lock = LOCK_INIT;
@@ -144,8 +150,10 @@ int reset_head(struct repository *r, struct object_id *oid,
 		goto leave_reset_head;
 	}
 
-	ret = update_refs(oid, switch_to_branch, head, reflog_head,
-			  reflog_orig_head, default_reflog_action, flags);
+	if (oid != &head_oid || update_orig_head || switch_to_branch)
+		ret = update_refs(oid, switch_to_branch, head, reflog_head,
+				  reflog_orig_head, default_reflog_action,
+				  flags);
 
 leave_reset_head:
 	rollback_lock_file(&lock);