parser: disallow the array init: attr, when the len: attr is not provided (#16735)

examples/graphs/bfs.v

@@ -16,7 +16,7 @@ fn main() {
 // Breadth-First Search (BFS) allows you to find the shortest distance between two nodes in the graph.
 fn breadth_first_search_path(graph map[string][]string, vertex string, target string) []string {
 	mut path := []string{}
-	mut visited := []string{init: vertex}
+	mut visited := []string{len: 6, init: vertex}
 	mut queue := [][][]string{}
 	queue << [[vertex], path]
 	for queue.len > 0 {

vlib/v/checker/tests/assign_expr_undefined_err_i.out

@@ -1,6 +1,6 @@
-vlib/v/checker/tests/assign_expr_undefined_err_i.vv:2:23: error: undefined variable: `a`
+vlib/v/checker/tests/assign_expr_undefined_err_i.vv:2:31: error: undefined variable: `a`
     1 | fn main() {
-    2 |     mut a := []int{init: a}
+    2 |     mut a := []int{len: 1, init: a}
       |                                  ^
     3 |     println(a)
     4 | }

vlib/v/checker/tests/assign_expr_undefined_err_i.vv

@@ -1,4 +1,4 @@
 fn main() {
-	mut a := []int{init: a}
+	mut a := []int{len: 1, init: a}
 	println(a)
 }

vlib/v/checker/tests/optional_fn_err.out

@@ -80,18 +80,18 @@ vlib/v/checker/tests/optional_fn_err.vv:56:8: error: bar() returns an option, so
    55 |     // init
    56 |     _ := [bar(0)]
       |           ~~~~~~
-   57 |     _ := []int{init: bar(0)}
+   57 |     _ := []int{len: 1, init: bar(0)}
    58 |     _ := [bar(0)]!
-vlib/v/checker/tests/optional_fn_err.vv:57:19: error: bar() returns an option, so it should have either an `or {}` block, or `?` at the end
+vlib/v/checker/tests/optional_fn_err.vv:57:27: error: bar() returns an option, so it should have either an `or {}` block, or `?` at the end
    55 |     // init
    56 |     _ := [bar(0)]
-   57 |     _ := []int{init: bar(0)}
+   57 |     _ := []int{len: 1, init: bar(0)}
       |                              ~~~~~~
    58 |     _ := [bar(0)]!
    59 |     _ := [1]int{init: bar(0)}
 vlib/v/checker/tests/optional_fn_err.vv:58:8: error: bar() returns an option, so it should have either an `or {}` block, or `?` at the end
    56 |     _ := [bar(0)]
-   57 |     _ := []int{init: bar(0)}
+   57 |     _ := []int{len: 1, init: bar(0)}
    58 |     _ := [bar(0)]!
       |           ~~~~~~
    59 |     _ := [1]int{init: bar(0)}

vlib/v/checker/tests/optional_fn_err.vv

@@ -54,7 +54,7 @@ fn main() {
 	arr << bar(0)
 	// init
 	_ := [bar(0)]
-	_ := []int{init: bar(0)}
+	_ := []int{len: 1, init: bar(0)}
 	_ := [bar(0)]!
 	_ := [1]int{init: bar(0)}
 	// index

vlib/v/parser/containers.v

@@ -4,6 +4,7 @@
 module parser
 
 import v.ast
+import v.token
 
 fn (mut p Parser) array_init() ast.ArrayInit {
 	first_pos := p.tok.pos()
@@ -132,10 +133,12 @@ fn (mut p Parser) array_init() ast.ArrayInit {
 	mut has_cap := false
 	mut len_expr := ast.empty_expr
 	mut cap_expr := ast.empty_expr
+	mut attr_pos := token.Pos{}
 	if p.tok.kind == .lcbr && exprs.len == 0 && array_type != ast.void_type {
 		// `[]int{ len: 10, cap: 100}` syntax
 		p.next()
 		for p.tok.kind != .rcbr {
+			attr_pos = p.tok.pos()
 			key := p.check_name()
 			p.check(.colon)
 			match key {
@@ -172,6 +175,10 @@ fn (mut p Parser) array_init() ast.ArrayInit {
 			}
 		}
 		p.check(.rcbr)
+		if has_default && !has_len {
+			p.error_with_pos('cannot use `init` attribute unless `len` attribute is also provided',
+				attr_pos)
+		}
 	}
 	pos := first_pos.extend_with_last_line(last_pos, p.prev_tok.line_nr)
 	return ast.ArrayInit{

vlib/v/parser/tests/array_init_given_len_not_given_err.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/array_init_given_len_not_given_err.vv:8:27: error: cannot use `init` attribute unless `len` attribute is also provided
+    6 | 
+    7 | fn main() {
+    8 |     mut list_elem := [][]f64{init: [0.0, 0.0]}
+      |                              ~~~~
+    9 |     mut elem := 0.0
+   10 |     for i in 0 .. lenn {

vlib/v/parser/tests/array_init_given_len_not_given_err.vv

@@ -0,0 +1,15 @@
+import rand
+
+const (
+	lenn = 100
+)
+
+fn main() {
+	mut list_elem := [][]f64{init: [0.0, 0.0]}
+	mut elem := 0.0
+	for i in 0 .. lenn {
+		elem = rand.int_in_range(-100000000, 100000001)!
+		list_elem[i] << [elem, elem]
+	}
+	println(list_elem)
+}