commit: fix empty commit creation when there's no changes but ita entries

If i-t-a entries are present and there is no change between the index
and HEAD i-t-a entries, index_differs_from() still returns "dirty, new
entries" (aka, the resulting commit is not empty), but cache-tree will
skip i-t-a entries and produce the exact same tree of current
commit.

index_differs_from() is supposed to catch this so we can abort
git-commit (unless --no-empty is specified). Update it to optionally
ignore i-t-a entries when doing a diff between the index and HEAD so
that it would return "no change" in this case and abort commit.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -910,7 +910,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 			if (ignore_submodule_arg &&
 			    !strcmp(ignore_submodule_arg, "all"))
 				diff_flags |= DIFF_OPT_IGNORE_SUBMODULES;
-			commitable = index_differs_from(parent, diff_flags);
+			commitable = index_differs_from(parent, diff_flags, 1);
 		}
 	}
 	strbuf_release(&committer_ident);

diff-lib.c

@@ -535,7 +535,8 @@ int do_diff_cache(const unsigned char *tree_sha1, struct diff_options *opt)
 	return 0;
 }
 
-int index_differs_from(const char *def, int diff_flags)
+int index_differs_from(const char *def, int diff_flags,
+		       int ita_invisible_in_index)
 {
 	struct rev_info rev;
 	struct setup_revision_opt opt;
@@ -547,6 +548,7 @@ int index_differs_from(const char *def, int diff_flags)
 	DIFF_OPT_SET(&rev.diffopt, QUICK);
 	DIFF_OPT_SET(&rev.diffopt, EXIT_WITH_STATUS);
 	rev.diffopt.flags |= diff_flags;
+	rev.diffopt.ita_invisible_in_index = ita_invisible_in_index;
 	run_diff_index(&rev, 1);
 	if (rev.pending.alloc)
 		free(rev.pending.objects);

diff.h

@@ -357,7 +357,7 @@ extern int diff_result_code(struct diff_options *, int);
 
 extern void diff_no_index(struct rev_info *, int, const char **);
 
-extern int index_differs_from(const char *def, int diff_flags);
+extern int index_differs_from(const char *def, int diff_flags, int ita_invisible_in_index);
 
 /*
  * Fill the contents of the filespec "df", respecting any textconv defined by

sequencer.c

@@ -469,7 +469,7 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 		unborn = get_sha1("HEAD", head);
 		if (unborn)
 			hashcpy(head, EMPTY_TREE_SHA1_BIN);
-		if (index_differs_from(unborn ? EMPTY_TREE_SHA1_HEX : "HEAD", 0))
+		if (index_differs_from(unborn ? EMPTY_TREE_SHA1_HEX : "HEAD", 0, 0))
 			return error_dirty_index(opts);
 	}
 	discard_cache();
@@ -1064,7 +1064,7 @@ static int sequencer_continue(struct replay_opts *opts)
 		if (ret)
 			return ret;
 	}
-	if (index_differs_from("HEAD", 0))
+	if (index_differs_from("HEAD", 0, 0))
 		return error_dirty_index(opts);
 	todo_list = todo_list->next;
 	return pick_commits(todo_list, opts);

t/t2203-add-intent.sh

@@ -129,5 +129,16 @@ test_expect_success 'cache-tree does skip dir that becomes empty' '
 	)
 '
 
+test_expect_success 'commit: ita entries ignored in empty commit check' '
+	git init empty-subsequent-commit &&
+	(
+		cd empty-subsequent-commit &&
+		test_commit one &&
+		: >two &&
+		git add -N two &&
+		test_must_fail git commit -m nothing-new-here
+	)
+'
+
 test_done