parser: allow using a, b and it as var names, when using the builtin array methods (fix #25729) (#25755)

Author: kbkpbot

vlib/v/parser/assign.v

@@ -49,6 +49,11 @@ fn (mut p Parser) check_undefined_variables(names []string, val ast.Expr) ! {
 		}
 		ast.CallExpr {
 			p.check_undefined_variables(names, val.left)!
+			// arr.sort(a < b) , arr.sorted(a < b), it := [2,3,4].map(it*2), it := [2,3,4].filter(it % 2 == 0), etc.
+			if val.args.len == 1
+				&& val.name in ['sort', 'sorted', 'map', 'filter', 'any', 'all', 'count'] {
+				return
+			}
 			for arg in val.args {
 				p.check_undefined_variables(names, arg.expr)!
 			}

vlib/v/tests/skip_sort_arg_check_test.v

@@ -0,0 +1,38 @@
+// should allow `a:=arr.sorted(a < b)` use `a` as var name
+fn test_skip_check_sort_arg_a_b() {
+	arr := [4, 2, 1, 3]
+	a := arr.sorted(a < b)
+	assert a == [1, 2, 3, 4]
+	b := arr.sorted(a > b)
+	assert b == [4, 3, 2, 1]
+}
+
+// should allow `it:=arr.map(it*2)` use `it` as var name
+fn test_skip_check_map_arg_it() {
+	it := [4, 2, 1, 3].map(it * 2)
+	assert it == [8, 4, 2, 6]
+}
+
+// should allow `it:=arr.filter(it%2==0)` use `it` as var name
+fn test_skip_check_filter_arg_it() {
+	it := [4, 2, 1, 3].filter(it % 2 == 0)
+	assert it == [4, 2]
+}
+
+// should allow `it:=arr.any(it%2==0)` use `it` as var name
+fn test_skip_check_any_arg_it() {
+	it := [4, 2, 1, 3].any(it % 2 == 0)
+	assert it
+}
+
+// should allow `it:=arr.all(it%2==0)` use `it` as var name
+fn test_skip_check_all_arg_it() {
+	it := [4, 2, 1, 3].all(it % 2 == 0)
+	assert !it
+}
+
+// should allow `it:=arr.count(it%2==0)` use `it` as var name
+fn test_skip_check_count_arg_it() {
+	it := [4, 2, 1, 3].count(it % 2 == 0)
+	assert it == 2
+}