checker: fix autocast in complex if condtions 2 (#18702)

vlib/v/checker/infix.v

@@ -17,6 +17,16 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 	if node.op == .and {
 		mut left_node := node.left
 		for mut left_node is ast.InfixExpr {
+			if left_node.op == .and && mut left_node.right is ast.InfixExpr {
+				if left_node.right.op == .key_is {
+					// search last `n is ast.Ident` in the left
+					from_type := c.expr(left_node.right.left)
+					to_type := c.expr(left_node.right.right)
+					c.autocast_in_if_conds(mut node.right, left_node.right.left, from_type,
+						to_type)
+					break
+				}
+			}
 			if left_node.op == .key_is {
 				// search `n is ast.Ident`
 				from_type := c.expr(left_node.left)
@@ -835,6 +845,16 @@ fn (mut c Checker) autocast_in_if_conds(mut right ast.Expr, from_expr ast.Expr,
 			c.autocast_in_if_conds(mut right.right, from_expr, from_type, to_type)
 		}
 		ast.CallExpr {
+			if right.left.str() == from_expr.str()
+				&& c.table.sym(to_type).has_method_with_generic_parent(right.name) {
+				right.left = ast.ParExpr{
+					expr: ast.AsCast{
+						typ: to_type
+						expr: from_expr
+						expr_type: from_type
+					}
+				}
+			}
 			c.autocast_in_if_conds(mut right.left, from_expr, from_type, to_type)
 			for mut arg in right.args {
 				c.autocast_in_if_conds(mut arg.expr, from_expr, from_type, to_type)

vlib/v/tests/autocast_in_if_conds_3_test.v

@@ -0,0 +1,45 @@
+type MySumType = S1 | S2
+
+struct Info {
+	name string
+}
+
+struct Node {
+	left MySumType
+}
+
+struct S1 {
+	is_info bool
+	info    Info
+}
+
+fn (s1 S1) is_info() bool {
+	return s1.is_info
+}
+
+struct S2 {
+	field2 string
+}
+
+fn get_name(name string) string {
+	return name
+}
+
+fn test_autocast_in_if_conds() {
+	node := Node{
+		left: MySumType(S1{
+			is_info: false
+			info: Info{'foo'}
+		})
+	}
+
+	a := 22
+
+	if a > 0 && node.left is S1 && !node.left.is_info && get_name(node.left.info.name) == 'foo'
+		&& !node.left.is_info() {
+		println('ok')
+		assert true
+	} else {
+		assert false
+	}
+}