Make "git notes add" more user-friendly when there are existing notes

Currently, "notes add" (without -f/--force) will abort when the given object
already has existing notes. This makes sense for the modes of "git notes add"
that would necessarily overwrite the old message (when using the -m/-F/-C/-c
options). However, when no options are given (meaning the notes are created
from scratch in the editor) it is not very user-friendly to abort on existing
notes, and forcing the user to run "git notes edit".

Instead, it is better to simply "redirect" to "git notes edit" automatically,
i.e. open the existing notes in the editor and let the user edit them.
This patch does just that.

This changes the behavior of "git notes add" without options when notes
already exist for the given object, but I doubt that many users really depend
on the previous failure from "git notes add" in this case.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-notes.txt

@@ -57,8 +57,11 @@ list::
 
 add::
 	Add notes for a given object (defaults to HEAD). Abort if the
-	object already has notes (use `-f` to overwrite an
-	existing note).
+	object already has notes (use `-f` to overwrite existing notes).
+	However, if you're using `add` interactively (using an editor
+	to supply the notes contents), then - instead of aborting -
+	the existing notes will be opened in the editor (like the `edit`
+	subcommand).
 
 copy::
 	Copy the notes for the first object onto the second object.

builtin/notes.c

@@ -527,6 +527,8 @@ static int list(int argc, const char **argv, const char *prefix)
 	return retval;
 }
 
+static int append_edit(int argc, const char **argv, const char *prefix);
+
 static int add(int argc, const char **argv, const char *prefix)
 {
 	int retval = 0, force = 0;
@@ -554,14 +556,14 @@ static int add(int argc, const char **argv, const char *prefix)
 	};
 
 	argc = parse_options(argc, argv, prefix, options, git_notes_add_usage,
-			     0);
+			     PARSE_OPT_KEEP_ARGV0);
 
-	if (1 < argc) {
+	if (2 < argc) {
 		error("too many parameters");
 		usage_with_options(git_notes_add_usage, options);
 	}
 
-	object_ref = argc ? argv[0] : "HEAD";
+	object_ref = argc > 1 ? argv[1] : "HEAD";
 
 	if (get_sha1(object_ref, object))
 		die("Failed to resolve '%s' as a valid ref.", object_ref);
@@ -571,6 +573,18 @@ static int add(int argc, const char **argv, const char *prefix)
 
 	if (note) {
 		if (!force) {
+			if (!msg.given) {
+				/*
+				 * Redirect to "edit" subcommand.
+				 *
+				 * We only end up here if none of -m/-F/-c/-C
+				 * or -f are given. The original args are
+				 * therefore still in argv[0-1].
+				 */
+				argv[0] = "edit";
+				free_notes(t);
+				return append_edit(argc, argv, prefix);
+			}
 			retval = error("Cannot add notes. Found existing notes "
 				       "for object %s. Use '-f' to overwrite "
 				       "existing notes", sha1_to_hex(object));

t/t3301-notes.sh

@@ -101,15 +101,33 @@ test_expect_success 'edit existing notes' '
 	test_must_fail git notes show HEAD^
 '
 
-test_expect_success 'cannot add note where one exists' '
-	! MSG=b2 git notes add &&
+test_expect_success 'cannot "git notes add -m" where notes already exists' '
+	test_must_fail git notes add -m "b2" &&
 	test ! -f .git/NOTES_EDITMSG &&
 	test 1 = $(git ls-tree refs/notes/commits | wc -l) &&
 	test b3 = $(git notes show) &&
 	git show HEAD^ &&
 	test_must_fail git notes show HEAD^
 '
 
+test_expect_success 'can overwrite existing note with "git notes add -f -m"' '
+	git notes add -f -m "b1" &&
+	test ! -f .git/NOTES_EDITMSG &&
+	test 1 = $(git ls-tree refs/notes/commits | wc -l) &&
+	test b1 = $(git notes show) &&
+	git show HEAD^ &&
+	test_must_fail git notes show HEAD^
+'
+
+test_expect_success 'add w/no options on existing note morphs into edit' '
+	MSG=b2 git notes add &&
+	test ! -f .git/NOTES_EDITMSG &&
+	test 1 = $(git ls-tree refs/notes/commits | wc -l) &&
+	test b2 = $(git notes show) &&
+	git show HEAD^ &&
+	test_must_fail git notes show HEAD^
+'
+
 test_expect_success 'can overwrite existing note with "git notes add -f"' '
 	MSG=b1 git notes add -f &&
 	test ! -f .git/NOTES_EDITMSG &&
@@ -194,6 +212,13 @@ test_expect_success 'show -F notes' '
 	test_cmp expect-F output
 '
 
+test_expect_success 'Re-adding -F notes without -f fails' '
+	echo "zyxxy" > note5 &&
+	test_must_fail git notes add -F note5 &&
+	git log -3 > output &&
+	test_cmp expect-F output
+'
+
 cat >expect << EOF
 commit 15023535574ded8b1a89052b32673f84cf9582b8
 tree e070e3af51011e47b183c33adf9736736a525709