tests: add recursive generics fn test (#9907)

vlib/v/tests/generics_with_recursive_generics_fn_test.v

@@ -0,0 +1,43 @@
+import rand
+
+const (
+	gen_len = 1000 // how many random numbers to generate
+	gen_max = 10000 // max of the generated numbers
+)
+
+fn test_generics_with_recursive_generics_fn() {
+	mut arr := []int{}
+	for _ in 0 .. gen_len {
+		arr << rand.intn(gen_max)
+	}
+	println('before quick sort whether array is sorted: ${is_sorted<int>(arr)}')
+	assert !is_sorted<int>(arr)
+	quick_sort<int>(mut arr, 0, arr.len - 1)
+	println('after quick sort whether array is sorted: ${is_sorted<int>(arr)}')
+	assert is_sorted<int>(arr)
+}
+
+fn quick_sort<T>(mut arr []T, l int, r int) {
+	if l >= r {
+		return
+	}
+	mut sep := l // what is sep: [...all_value<arr[sep]...sep...all_value>=arr[sep]...]
+	for i in l + 1 .. r + 1 {
+		if arr[i] < arr[l] {
+			sep++
+			arr[i], arr[sep] = arr[sep], arr[i]
+		}
+	}
+	arr[l], arr[sep] = arr[sep], arr[l]
+	quick_sort<T>(mut arr, l, sep - 1)
+	quick_sort<T>(mut arr, sep + 1, r)
+}
+
+fn is_sorted<T>(arr []T) bool {
+	for i in 0 .. arr.len - 1 {
+		if arr[i] > arr[i + 1] {
+			return false
+		}
+	}
+	return true
+}