commit --amend: copy notes to the new commit

Teaches 'git commit --amend' to copy notes.  The catch is that this
must also be guarded by --no-post-rewrite, which we use to prevent
--amend from copying notes during a rebase -i 'edit'/'reword'.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-commit.c

@@ -1340,6 +1340,12 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	rerere(0);
 	run_hook(get_index_file(), "post-commit", NULL);
 	if (amend && !no_post_rewrite) {
+		struct notes_rewrite_cfg *cfg;
+		cfg = init_copy_notes_for_rewrite("amend");
+		if (cfg) {
+			copy_note_for_rewrite(cfg, head_sha1, commit_sha1);
+			finish_copy_notes_for_rewrite(cfg);
+		}
 		run_rewrite_hook(head_sha1, commit_sha1);
 	}
 	if (!quiet)

t/t7501-commit.sh

@@ -425,4 +425,16 @@ test_expect_success 'amend using the message from a commit named with tag' '
 
 '
 
+test_expect_success 'amend can copy notes' '
+
+	git config notes.rewrite.amend true &&
+	git config notes.rewriteRef "refs/notes/*" &&
+	test_commit foo &&
+	git notes add -m"a note" &&
+	test_tick &&
+	git commit --amend -m"new foo" &&
+	test "$(git notes show)" = "a note"
+
+'
+
 test_done