strvec: introduce new `strvec_splice()` function

Introduce a new `strvec_splice()` function that can replace a range of
strings in the vector with another array of strings. This function will
be used in subsequent commits.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strvec.c

@@ -56,6 +56,25 @@ void strvec_pushv(struct strvec *array, const char **items)
 		strvec_push(array, *items);
 }
 
+void strvec_splice(struct strvec *array, size_t idx, size_t len,
+		   const char **replacement, size_t replacement_len)
+{
+	if (idx + len > array->nr)
+		BUG("range outside of array boundary");
+	if (replacement_len > len)
+		ALLOC_GROW(array->v, array->nr + (replacement_len - len) + 1,
+			   array->alloc);
+	for (size_t i = 0; i < len; i++)
+		free((char *)array->v[idx + i]);
+	if (replacement_len != len) {
+		memmove(array->v + idx + replacement_len, array->v + idx + len,
+			(array->nr - idx - len + 1) * sizeof(char *));
+		array->nr += (replacement_len - len);
+	}
+	for (size_t i = 0; i < replacement_len; i++)
+		array->v[idx + i] = xstrdup(replacement[i]);
+}
+
 const char *strvec_replace(struct strvec *array, size_t idx, const char *replacement)
 {
 	char *to_free;

strvec.h

@@ -67,6 +67,15 @@ void strvec_pushl(struct strvec *, ...);
 /* Push a null-terminated array of strings onto the end of the array. */
 void strvec_pushv(struct strvec *, const char **);
 
+/*
+ * Replace `len` values starting at `idx` with the provided replacement
+ * strings. If `len` is zero this is effectively an insert at the given `idx`.
+ * If `replacement_len` is zero this is effectively a delete of `len` items
+ * starting at `idx`.
+ */
+void strvec_splice(struct strvec *array, size_t idx, size_t len,
+		   const char **replacement, size_t replacement_len);
+
 /**
  * Replace the value at the given index with a new value. The index must be
  * valid. Returns a pointer to the inserted value.

t/unit-tests/strvec.c

@@ -88,6 +88,71 @@ void test_strvec__pushv(void)
 	strvec_clear(&vec);
 }
 
+void test_strvec__splice_with_same_size_replacement(void)
+{
+	struct strvec vec = STRVEC_INIT;
+	const char *replacement[] = { "1" };
+
+	strvec_pushl(&vec, "foo", "bar", "baz", NULL);
+	strvec_splice(&vec, 1, 1, replacement, ARRAY_SIZE(replacement));
+	check_strvec(&vec, "foo", "1", "baz", NULL);
+	strvec_clear(&vec);
+}
+
+void test_strvec__splice_with_smaller_replacement(void)
+{
+	struct strvec vec = STRVEC_INIT;
+	const char *replacement[] = { "1" };
+
+	strvec_pushl(&vec, "foo", "bar", "baz", NULL);
+	strvec_splice(&vec, 1, 2, replacement, ARRAY_SIZE(replacement));
+	check_strvec(&vec, "foo", "1", NULL);
+	strvec_clear(&vec);
+}
+
+void test_strvec__splice_with_bigger_replacement(void)
+{
+	struct strvec vec = STRVEC_INIT;
+	const char *replacement[] = { "1", "2", "3" };
+
+	strvec_pushl(&vec, "foo", "bar", "baz", NULL);
+	strvec_splice(&vec, 0, 2, replacement, ARRAY_SIZE(replacement));
+	check_strvec(&vec, "1", "2", "3", "baz", NULL);
+	strvec_clear(&vec);
+}
+
+void test_strvec__splice_with_empty_replacement(void)
+{
+	struct strvec vec = STRVEC_INIT;
+
+	strvec_pushl(&vec, "foo", "bar", "baz", NULL);
+	strvec_splice(&vec, 0, 2, NULL, 0);
+	check_strvec(&vec, "baz", NULL);
+	strvec_clear(&vec);
+}
+
+void test_strvec__splice_with_empty_original(void)
+{
+	struct strvec vec = STRVEC_INIT;
+	const char *replacement[] = { "1", "2" };
+
+	strvec_pushl(&vec, "foo", "bar", "baz", NULL);
+	strvec_splice(&vec, 1, 0, replacement, ARRAY_SIZE(replacement));
+	check_strvec(&vec, "foo", "1", "2", "bar", "baz", NULL);
+	strvec_clear(&vec);
+}
+
+void test_strvec__splice_at_tail(void)
+{
+	struct strvec vec = STRVEC_INIT;
+	const char *replacement[] = { "1", "2" };
+
+	strvec_pushl(&vec, "foo", "bar", NULL);
+	strvec_splice(&vec, 2, 0, replacement, ARRAY_SIZE(replacement));
+	check_strvec(&vec, "foo", "bar", "1", "2", NULL);
+	strvec_clear(&vec);
+}
+
 void test_strvec__replace_at_head(void)
 {
 	struct strvec vec = STRVEC_INIT;