[PATCH v3 3/3] tag: keep the message file in case ref transaction fails

[Kristoffer Haugsbakk <code@xxxxxxxxxxxxxxx>]

The ref transaction can fail after the user has written their tag
message. In particular, if there exists a tag `foo/bar` and `git tag -a
foo` is said then the command will only fail once it tries to write
`refs/tags/foo`, which is after the file has been unlinked.

Hold on to the message file for a little longer so that it is not
unlinked before the fatal error occurs.

Signed-off-by: Kristoffer Haugsbakk <code@xxxxxxxxxxxxxxx>
---

Notes (series):
    § From v2
    
    (Noting for other reviewers (after v2):)
    
    I duplicated this message (this isn’t obvious in the diff):
    
        fprintf(stderr,
                _("The tag message has been left in %s\n"),
                path);

 builtin/tag.c  | 24 +++++++++++++++---------
 t/t7004-tag.sh | 10 ++++++++++
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/builtin/tag.c b/builtin/tag.c
index d428c45dc8d..7df9c143ac0 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -266,11 +266,10 @@ static const char message_advice_nested_tag[] =
 static void create_tag(const struct object_id *object, const char *object_ref,
 		       const char *tag,
 		       struct strbuf *buf, struct create_tag_options *opt,
-		       struct object_id *prev, struct object_id *result)
+		       struct object_id *prev, struct object_id *result, char *path)
 {
 	enum object_type type;
 	struct strbuf header = STRBUF_INIT;
-	char *path = NULL;
 
 	type = oid_object_info(the_repository, object, NULL);
 	if (type <= OBJ_NONE)
@@ -294,7 +293,6 @@ static void create_tag(const struct object_id *object, const char *object_ref,
 		int fd;
 
 		/* write the template message before editing: */
-		path = git_pathdup("TAG_EDITMSG");
 		fd = xopen(path, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 
 		if (opt->message_given) {
@@ -336,10 +334,6 @@ static void create_tag(const struct object_id *object, const char *object_ref,
 				path);
 		exit(128);
 	}
-	if (path) {
-		unlink_or_warn(path);
-		free(path);
-	}
 }
 
 static void create_reflog_msg(const struct object_id *oid, struct strbuf *sb)
@@ -487,6 +481,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	};
 	int ret = 0;
 	const char *only_in_list = NULL;
+	char *path = NULL;
 
 	setup_ref_filter_porcelain_msg();
 
@@ -621,7 +616,9 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	if (create_tag_object) {
 		if (force_sign_annotate && !annotate)
 			opt.sign = 1;
-		create_tag(&object, object_ref, tag, &buf, &opt, &prev, &object);
+		path = git_pathdup("TAG_EDITMSG");
+		create_tag(&object, object_ref, tag, &buf, &opt, &prev, &object,
+			   path);
 	}
 
 	transaction = ref_transaction_begin(&err);
@@ -629,8 +626,17 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	    ref_transaction_update(transaction, ref.buf, &object, &prev,
 				   create_reflog ? REF_FORCE_CREATE_REFLOG : 0,
 				   reflog_msg.buf, &err) ||
-	    ref_transaction_commit(transaction, &err))
+	    ref_transaction_commit(transaction, &err)) {
+		if (path)
+			fprintf(stderr,
+				_("The tag message has been left in %s\n"),
+				path);
 		die("%s", err.buf);
+	}
+	if (path) {
+		unlink_or_warn(path);
+		free(path);
+	}
 	ref_transaction_free(transaction);
 	if (force && !is_null_oid(&prev) && !oideq(&prev, &object))
 		printf(_("Updated tag '%s' (was %s)\n"), tag,
diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index 1cb738b00d2..e6f9579cff7 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -2136,4 +2136,14 @@ test_expect_success 'If tag is created then tag message file is unlinked' '
 	test_path_is_missing .git/TAG_EDITMSG
 '
 
+test_expect_success 'If tag cannot be created then tag message file is not unlinked' '
+	test_when_finished "git tag -d foo/bar && rm .git/TAG_EDITMSG" &&
+	write_script fakeeditor <<-\EOF &&
+	echo Message >.git/TAG_EDITMSG
+	EOF
+	git tag foo/bar &&
+	test_must_fail env GIT_EDITOR=./fakeeditor git tag -a foo &&
+	test_path_exists .git/TAG_EDITMSG
+'
+
 test_done
-- 
2.40.1