notes: do not trigger editor when adding an empty note

With "git notes add -C $blob", the given blob contents are to be made
into a note without involving an editor.  But when "--allow-empty" is
given, the editor is invoked, which can cause problems for
non-interactive callers[1].

This behaviour started with 90bc19b (notes.c: introduce
'--separator=<paragraph-break>' option, 2023-05-27), which changed
editor invocation logic to check for a zero length note_data buffer.

Restore the original behaviour of "git note" that takes the contents
given via the "-m", "-C", "-F" options without invoking an editor, by
checking for any prior parameter callbacks, indicated by a non-zero
note_data.msg_nr.  Remove the now-unneeded note_data.given flag.

Add a test for this regression by checking whether GIT_EDITOR is
invoked alongside "git notes add -C $empty_blob --allow-empty"

[1] ddiss/icyci#12

Signed-off-by: David Disseldorp <ddiss@suse.de>
[jc: enhanced the test with -m/-F options]
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ddiss

builtin/notes.c

@@ -114,7 +114,6 @@ struct note_msg {
 };
 
 struct note_data {
-	int given;
 	int use_editor;
 	int stripspace;
 	char *edit_path;
@@ -193,15 +192,15 @@ static void write_commented_object(int fd, const struct object_id *object)
 static void prepare_note_data(const struct object_id *object, struct note_data *d,
 		const struct object_id *old_note)
 {
-	if (d->use_editor || !d->given) {
+	if (d->use_editor || !d->msg_nr) {
 		int fd;
 		struct strbuf buf = STRBUF_INIT;
 
 		/* write the template message before editing: */
 		d->edit_path = git_pathdup("NOTES_EDITMSG");
 		fd = xopen(d->edit_path, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 
-		if (d->given)
+		if (d->msg_nr)
 			write_or_die(fd, d->buf.buf, d->buf.len);
 		else if (old_note)
 			copy_obj_to_fd(fd, old_note);
@@ -515,7 +514,6 @@ static int add(int argc, const char **argv, const char *prefix)
 
 	if (d.msg_nr)
 		concat_messages(&d);
-	d.given = !!d.buf.len;
 
 	object_ref = argc > 1 ? argv[1] : "HEAD";
 
@@ -528,7 +526,7 @@ static int add(int argc, const char **argv, const char *prefix)
 	if (note) {
 		if (!force) {
 			free_notes(t);
-			if (d.given) {
+			if (d.msg_nr) {
 				free_note_data(&d);
 				return error(_("Cannot add notes. "
 					"Found existing notes for object %s. "
@@ -690,14 +688,14 @@ static int append_edit(int argc, const char **argv, const char *prefix)
 		usage_with_options(usage, options);
 	}
 
-	if (d.msg_nr)
+	if (d.msg_nr) {
 		concat_messages(&d);
-	d.given = !!d.buf.len;
-
-	if (d.given && edit)
-		fprintf(stderr, _("The -m/-F/-c/-C options have been deprecated "
-			"for the 'edit' subcommand.\n"
-			"Please use 'git notes add -f -m/-F/-c/-C' instead.\n"));
+		if (edit)
+			fprintf(stderr, _("The -m/-F/-c/-C options have been "
+				"deprecated for the 'edit' subcommand.\n"
+				"Please use 'git notes add -f -m/-F/-c/-C' "
+				"instead.\n"));
+	}
 
 	object_ref = 1 < argc ? argv[1] : "HEAD";
 

t/t3301-notes.sh

@@ -1557,4 +1557,14 @@ test_expect_success 'empty notes are displayed by git log' '
 	test_cmp expect actual
 '
 
+test_expect_success 'empty notes do not invoke the editor' '
+	test_commit 18th &&
+	GIT_EDITOR="false" git notes add -C "$empty_blob" --allow-empty &&
+	git notes remove HEAD &&
+	GIT_EDITOR="false" git notes add -m "" --allow-empty &&
+	git notes remove HEAD &&
+	GIT_EDITOR="false" git notes add -F /dev/null --allow-empty &&
+	git notes remove HEAD
+'
+
 test_done