Subject: [PATCH v3 6/7] string-list: optionally omit empty string pieces in string_list_split*()

From: Junio C Hamano <[email-masked]>
Date: Fri, 1 Aug 2025 15:04:22 -0700

Teach the unified split_string() machinery a new flag bit,
STRING_LIST_SPLIT_NONEMPTY, to cause empty split pieces to be
omitted from the resulting string list.

Signed-off-by: Junio C Hamano <[email-masked]>
---
 string-list.c                |  3 +++
 string-list.h                |  2 ++
 t/unit-tests/u-string-list.c | 15 +++++++++++++++
 3 files changed, 20 insertions(+)

diff --git a/string-list.c b/string-list.c
index 86a309f8fb..343cf1ca90 100644
--- a/string-list.c
+++ b/string-list.c
@@ -294,6 +294,9 @@ static int append_one(struct string_list *list,
 				break;
 	}
 
+	if ((flags & STRING_LIST_SPLIT_NONEMPTY) && (end <= p))
+		return 0;
+
 	if (in_place) {
 		*((char *)end) = '\0';
 		string_list_append(list, p);
diff --git a/string-list.h b/string-list.h
index 87ccc5f1e6..c25f28e9a3 100644
--- a/string-list.h
+++ b/string-list.h
@@ -286,6 +286,8 @@ int string_list_split_in_place(struct string_list *list, char *string,
 enum {
 	/* trim() resulting string piece before adding it to the list */
 	STRING_LIST_SPLIT_TRIM = (1 << 0),
+	/* omit adding empty string piece to the resulting list */
+	STRING_LIST_SPLIT_NONEMPTY = (1 << 1),
 };
 
 int string_list_split_f(struct string_list *, const char *string,
diff --git a/t/unit-tests/u-string-list.c b/t/unit-tests/u-string-list.c
index daa9307e45..a2457d7b1e 100644
--- a/t/unit-tests/u-string-list.c
+++ b/t/unit-tests/u-string-list.c
@@ -92,6 +92,13 @@ void test_string_list__split_f(void)
 			      "foo", "bar", "baz", NULL);
 	t_string_list_split_f("  a  b c  ", " ", 1, STRING_LIST_SPLIT_TRIM,
 			      "a", "b c", NULL);
+	t_string_list_split_f("::foo::bar:baz:", ":", -1, STRING_LIST_SPLIT_NONEMPTY,
+			      "foo", "bar", "baz", NULL);
+	t_string_list_split_f("foo:baz", ":", -1, STRING_LIST_SPLIT_NONEMPTY,
+			      "foo", "baz", NULL);
+	t_string_list_split_f("foo :: : baz", ":", -1,
+			      STRING_LIST_SPLIT_NONEMPTY | STRING_LIST_SPLIT_TRIM,
+			      "foo", "baz", NULL);
 }
 
 static void t_string_list_split_in_place_f(const char *data_, const char *delim,
@@ -125,6 +132,14 @@ void test_string_list__split_in_place_f(void)
 				       "foo", "bar", "baz", NULL);
 	t_string_list_split_in_place_f("  a  b c  ", " ", 1, STRING_LIST_SPLIT_TRIM,
 				       "a", "b c", NULL);
+	t_string_list_split_in_place_f("::foo::bar:baz:", ":", -1,
+				       STRING_LIST_SPLIT_NONEMPTY,
+				       "foo", "bar", "baz", NULL);
+	t_string_list_split_in_place_f("foo:baz", ":", -1, STRING_LIST_SPLIT_NONEMPTY,
+				       "foo", "baz", NULL);
+	t_string_list_split_in_place_f("foo :: : baz", ":", -1,
+				       STRING_LIST_SPLIT_NONEMPTY | STRING_LIST_SPLIT_TRIM,
+				       "foo", "baz", NULL);
 }
 
 void test_string_list__split(void)
-- 
2.50.1-633-g85c5610de3