merge: add scissors line on merge conflict

This fixes a bug where the scissors line is placed after the Conflicts:
section, in the case where a merge conflict occurs and
commit.cleanup = scissors.

Next, if commit.cleanup = scissors is specified, don't produce a
scissors line in commit if one already exists in the MERGE_MSG file.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/merge-options.txt

@@ -33,8 +33,11 @@ updated behaviour, the environment variable `GIT_MERGE_AUTOEDIT` can be
 set to `no` at the beginning of them.
 
 --cleanup=<mode>::
-	This option determines how the merge message will be cleaned up
-	before commiting. See linkgit:git-commit[1] for more details.
+	This option determines how the merge message will be cleaned up before
+	commiting. See linkgit:git-commit[1] for more details. In addition, if
+	the '<mode>' is given a value of `scissors`, scissors will be appended
+	to `MERGE_MSG` before being passed on to the commit machinery in the
+	case of a merge conflict.
 
 --ff::
 	When the merge resolves as a fast-forward, only update the branch

builtin/commit.c

@@ -668,6 +668,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	const char *hook_arg2 = NULL;
 	int clean_message_contents = (cleanup_mode != COMMIT_MSG_CLEANUP_NONE);
 	int old_display_comment_prefix;
+	int merge_contains_scissors = 0;
 
 	/* This checks and barfs if author is badly specified */
 	determine_author_info(author_ident);
@@ -728,6 +729,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 			strbuf_addbuf(&sb, &message);
 		hook_arg1 = "message";
 	} else if (!stat(git_path_merge_msg(the_repository), &statbuf)) {
+		size_t merge_msg_start;
+
 		/*
 		 * prepend SQUASH_MSG here if it exists and a
 		 * "merge --squash" was originally performed
@@ -738,8 +741,16 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 			hook_arg1 = "squash";
 		} else
 			hook_arg1 = "merge";
+
+		merge_msg_start = sb.len;
 		if (strbuf_read_file(&sb, git_path_merge_msg(the_repository), 0) < 0)
 			die_errno(_("could not read MERGE_MSG"));
+
+		if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS &&
+		    wt_status_locate_end(sb.buf + merge_msg_start,
+					 sb.len - merge_msg_start) <
+				sb.len - merge_msg_start)
+			merge_contains_scissors = 1;
 	} else if (!stat(git_path_squash_msg(the_repository), &statbuf)) {
 		if (strbuf_read_file(&sb, git_path_squash_msg(the_repository), 0) < 0)
 			die_errno(_("could not read SQUASH_MSG"));
@@ -807,7 +818,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		struct ident_split ci, ai;
 
 		if (whence != FROM_COMMIT) {
-			if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS)
+			if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS &&
+				!merge_contains_scissors)
 				wt_status_add_cut_line(s->fp);
 			status_printf_ln(s, GIT_COLOR_NORMAL,
 			    whence == FROM_MERGE
@@ -832,10 +844,10 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 				_("Please enter the commit message for your changes."
 				  " Lines starting\nwith '%c' will be ignored, and an empty"
 				  " message aborts the commit.\n"), comment_line_char);
-		else if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS &&
-			 whence == FROM_COMMIT)
-			wt_status_add_cut_line(s->fp);
-		else /* COMMIT_MSG_CLEANUP_SPACE, that is. */
+		else if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS) {
+			if (whence == FROM_COMMIT && !merge_contains_scissors)
+				wt_status_add_cut_line(s->fp);
+		} else /* COMMIT_MSG_CLEANUP_SPACE, that is. */
 			status_printf(s, GIT_COLOR_NORMAL,
 				_("Please enter the commit message for your changes."
 				  " Lines starting\n"

builtin/merge.c

@@ -920,6 +920,20 @@ static int suggest_conflicts(void)
 	filename = git_path_merge_msg(the_repository);
 	fp = xfopen(filename, "a");
 
+	/*
+	 * We can't use cleanup_mode because if we're not using the editor,
+	 * get_cleanup_mode will return COMMIT_MSG_CLEANUP_SPACE instead, even
+	 * though the message is meant to be processed later by git-commit.
+	 * Thus, we will get the cleanup mode which is returned when we _are_
+	 * using an editor.
+	 */
+	if (get_cleanup_mode(cleanup_arg, 1) == COMMIT_MSG_CLEANUP_SCISSORS) {
+	    fputc('\n', fp);
+	    wt_status_add_cut_line(fp);
+	    /* comments out the newline from append_conflicts_hint */
+	    fputc(comment_line_char, fp);
+	}
+
 	append_conflicts_hint(&the_index, &msgbuf);
 	fputs(msgbuf.buf, fp);
 	strbuf_release(&msgbuf);

t/t7600-merge.sh

@@ -246,6 +246,52 @@ test_expect_success 'merge --squash c3 with c7' '
 	test_cmp expect actual
 '
 
+test_expect_success 'merge c3 with c7 with commit.cleanup = scissors' '
+	git config commit.cleanup scissors &&
+	git reset --hard c3 &&
+	test_must_fail git merge c7 &&
+	cat result.9z >file &&
+	git commit --no-edit -a &&
+
+	cat >expect <<-\EOF &&
+	Merge tag '"'"'c7'"'"'
+
+	# ------------------------ >8 ------------------------
+	# Do not modify or remove the line above.
+	# Everything below it will be ignored.
+	#
+	# Conflicts:
+	#	file
+	EOF
+	git cat-file commit HEAD >raw &&
+	sed -e '1,/^$/d' raw >actual &&
+	test_i18ncmp expect actual
+'
+
+test_expect_success 'merge c3 with c7 with --squash commit.cleanup = scissors' '
+	git config commit.cleanup scissors &&
+	git reset --hard c3 &&
+	test_must_fail git merge --squash c7 &&
+	cat result.9z >file &&
+	git commit --no-edit -a &&
+
+	cat >expect <<-EOF &&
+	Squashed commit of the following:
+
+	$(git show -s c7)
+
+	# ------------------------ >8 ------------------------
+	# Do not modify or remove the line above.
+	# Everything below it will be ignored.
+	#
+	# Conflicts:
+	#	file
+	EOF
+	git cat-file commit HEAD >raw &&
+	sed -e '1,/^$/d' raw >actual &&
+	test_i18ncmp expect actual
+'
+
 test_debug 'git log --graph --decorate --oneline --all'
 
 test_expect_success 'merge c1 with c2 and c3' '