ls-files: add %(objecttype) atom to format option

Sometimes users may want to align the feature of
`git ls-files --format` with that of `git ls-tree --format`,
but the %(objecttype) atom is missing in the format option
of git ls-files compared to git ls-tree.

Therefore, the %(objecttype) atom is added to the format option
of git ls-files, which can be used to obtain the object type
of the file which is recorded in the index.

Signed-off-by: ZheNing Hu <adlternative@gmail.com>

Documentation/git-ls-files.txt

@@ -270,6 +270,8 @@ interpolated.  The following "fieldname" are understood:
 
 objectmode::
 	The mode of the file which is recorded in the index.
+objecttype::
+	The object type of the file which is recorded in the index.
 objectname::
 	The name of the file which is recorded in the index.
 stage::

builtin/ls-files.c

@@ -272,6 +272,8 @@ static size_t expand_show_index(struct strbuf *sb, const char *start,
 		strbuf_addf(sb, "%06o", data->ce->ce_mode);
 	else if (skip_prefix(start, "(objectname)", &p))
 		strbuf_add_unique_abbrev(sb, &data->ce->oid, abbrev);
+	else if (skip_prefix(start, "(objecttype)", &p))
+		strbuf_addstr(sb, type_name(object_type(data->ce->ce_mode)));
 	else if (skip_prefix(start, "(stage)", &p))
 		strbuf_addf(sb, "%d", ce_stage(data->ce));
 	else if (skip_prefix(start, "(eolinfo:index)", &p))

t/t3013-ls-files-format.sh

@@ -38,6 +38,13 @@ test_expect_success 'git ls-files --format objectname v.s. -s' '
 	test_cmp expect actual
 '
 
+test_expect_success 'git ls-files --format objecttype' '
+	git ls-files --format="%(objectname)" o1.txt o4.txt o6.txt >objectname &&
+	git cat-file --batch-check="%(objecttype)" >expect <objectname &&
+	git ls-files --format="%(objecttype)" o1.txt o4.txt o6.txt >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'git ls-files --format v.s. --eol' '
 	git ls-files --eol >tmp &&
 	sed -e "s/	/ /g" -e "s/  */ /g" tmp >expect 2>err &&