rebase --abort: improve reflog message

When aborting a rebase the reflog message looks like

	rebase (abort): updating HEAD

which is not very informative. Improve the message by mentioning the
branch that we are returning to as we do at the end of a successful
rebase so it looks like.

	rebase (abort): returning to refs/heads/topic

If GIT_REFLOG_ACTION is set in the environment we no longer omit
"(abort)" from the reflog message. We don't omit "(start)" and
"(finish)" when starting and finishing a rebase in that case so we
shouldn't omit "(abort)".

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

builtin/rebase.c

@@ -1001,23 +1001,6 @@ static void NORETURN error_on_missing_default_upstream(void)
 	exit(1);
 }
 
-static void set_reflog_action(struct rebase_options *options)
-{
-	const char *env;
-	struct strbuf buf = STRBUF_INIT;
-
-	if (!is_merge(options))
-		return;
-
-	env = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
-	if (env && strcmp("rebase", env))
-		return; /* only override it if it is "rebase" */
-
-	strbuf_addf(&buf, "rebase (%s)", options->action);
-	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, buf.buf, 1);
-	strbuf_release(&buf);
-}
-
 static int check_exec_cmd(const char *cmd)
 {
 	if (strchr(cmd, '\n'))
@@ -1311,18 +1294,23 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 	case ACTION_ABORT: {
 		struct string_list merge_rr = STRING_LIST_INIT_DUP;
-		options.action = "abort";
-		set_reflog_action(&options);
+		struct strbuf head_msg = STRBUF_INIT;
 
+		options.action = "abort";
 		rerere_clear(the_repository, &merge_rr);
 		string_list_clear(&merge_rr, 1);
 
 		if (read_basic_state(&options))
 			exit(1);
+
+		strbuf_addf(&head_msg, "%s (abort): returning to %s",
+			    getenv(GIT_REFLOG_ACTION_ENVIRONMENT),
+			    options.head_name ? options.head_name
+					      : oid_to_hex(&options.orig_head->object.oid));
 		ropts.oid = &options.orig_head->object.oid;
+		ropts.head_msg = head_msg.buf;
 		ropts.branch = options.head_name;
 		ropts.flags = RESET_HEAD_HARD;
-		ropts.default_reflog_action = DEFAULT_REFLOG_ACTION;
 		if (reset_head(the_repository, &ropts) < 0)
 			die(_("could not move back to %s"),
 			    oid_to_hex(&options.orig_head->object.oid));

t/t3406-rebase-message.sh

@@ -187,6 +187,57 @@ test_reflog () {
 	EOF
 	test_cmp expect actual
 	'
+
+	test_expect_success "rebase $mode --abort reflog${reflog_action:+ GIT_REFLOG_ACTION=$reflog_action}" '
+	git checkout conflicts &&
+	test_when_finished "git reset --hard Q" &&
+
+	git log -g -1 conflicts >branch-expect &&
+	(
+		if test -n "$reflog_action"
+		then
+			GIT_REFLOG_ACTION="$reflog_action" &&
+			export GIT_REFLOG_ACTION
+		fi &&
+		test_must_fail git rebase $mode main &&
+		git rebase --abort
+	) &&
+
+	git log -g --format=%gs -3 >actual &&
+	write_reflog_expect <<-EOF &&
+	${reflog_action:-rebase} (abort): returning to refs/heads/conflicts
+	${reflog_action:-rebase} (pick): P
+	${reflog_action:-rebase} (start): checkout main
+	EOF
+	test_cmp expect actual &&
+
+	# check branch reflog is unchanged
+	git log -g -1 conflicts >branch-actual &&
+	test_cmp branch-expect branch-actual
+	'
+
+	test_expect_success "rebase $mode --abort detached HEAD reflog${reflog_action:+ GIT_REFLOG_ACTION=$reflog_action}" '
+	git checkout Q &&
+	test_when_finished "git reset --hard Q" &&
+
+	(
+		if test -n "$reflog_action"
+		then
+			GIT_REFLOG_ACTION="$reflog_action" &&
+			export GIT_REFLOG_ACTION
+		fi &&
+		test_must_fail git rebase $mode main &&
+		git rebase --abort
+	) &&
+
+	git log -g --format=%gs -3 >actual &&
+	write_reflog_expect <<-EOF &&
+	${reflog_action:-rebase} (abort): returning to $(git rev-parse Q)
+	${reflog_action:-rebase} (pick): P
+	${reflog_action:-rebase} (start): checkout main
+	EOF
+	test_cmp expect actual
+	'
 }
 
 test_reflog --merge