vector: do not malloc 0-length vectors on dup

src/vector.c

@@ -50,22 +50,24 @@ int git_vector_size_hint(git_vector *v, size_t size_hint)
 
 int git_vector_dup(git_vector *v, const git_vector *src, git_vector_cmp cmp)
 {
-	size_t bytes;
-
 	assert(v && src);
 
-	GITERR_CHECK_ALLOC_MULTIPLY(&bytes, src->length, sizeof(void *));
-
-	v->_alloc_size = src->length;
+	v->_alloc_size = 0;
+	v->contents = NULL;
 	v->_cmp = cmp ? cmp : src->_cmp;
 	v->length = src->length;
 	v->flags  = src->flags;
 	if (cmp != src->_cmp)
 		git_vector_set_sorted(v, 0);
+
+	if (src->length) {
+		size_t bytes;
+		GITERR_CHECK_ALLOC_MULTIPLY(&bytes, src->length, sizeof(void *));
 		v->contents = git__malloc(bytes);
 		GITERR_CHECK_ALLOC(v->contents);
-
+		v->_alloc_size = src->length;
 		memcpy(v->contents, src->contents, bytes);
+	}
 
 	return 0;
 }

tests/core/vector.c

@@ -407,3 +407,22 @@ void test_core_vector__reverse(void)
 
 	git_vector_free(&v);
 }
+
+void test_core_vector__dup_empty_vector(void)
+{
+	git_vector v = GIT_VECTOR_INIT;
+	git_vector dup = GIT_VECTOR_INIT;
+	void *dummy = 0xDEAFBEEB;
+
+	cl_assert_equal_i(0, v.length);
+
+	cl_git_pass(git_vector_dup(&dup, &v, v._cmp));
+	cl_assert_equal_i(0, dup._alloc_size);
+	cl_assert_equal_i(0, dup.length);
+
+	cl_git_pass(git_vector_insert(&dup, dummy));
+	cl_assert_equal_i(8, dup._alloc_size);
+	cl_assert_equal_i(1, dup.length);
+
+	git_vector_free(&dup);
+}