checker: disallow non_opt_array << optvalue (#20573)

Author: Delta456

vlib/v/checker/infix.v

@@ -529,6 +529,10 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 				node.auto_locked, _ = c.fail_if_immutable(mut node.left)
 				left_value_type := c.table.value_type(c.unwrap_generic(left_type))
 				left_value_sym := c.table.sym(c.unwrap_generic(left_value_type))
+				if !left_value_type.has_flag(.option) && right_type.has_flag(.option) {
+					c.error('unwrapped Option cannot be used in an infix expression',
+						node.pos)
+				}
 				if left_value_sym.kind == .interface_ {
 					if right_final_sym.kind != .array {
 						// []Animal << Cat

vlib/v/checker/tests/non_optional_array_append_optional_type_err.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/non_optional_array_append_optional_type_err.vv:12:10: error: unwrapped Option cannot be used in an infix expression
+   10 | fn main() {
+   11 |     mut foobars := []Foobar{}
+   12 |     foobars << ?Foobar(.foo)
+      |             ~~
+   13 |     foobars << get_foo_or_none(true)
+   14 | }
+vlib/v/checker/tests/non_optional_array_append_optional_type_err.vv:13:10: error: unwrapped Option cannot be used in an infix expression
+   11 |     mut foobars := []Foobar{}
+   12 |     foobars << ?Foobar(.foo)
+   13 |     foobars << get_foo_or_none(true)
+      |             ~~
+   14 | }

vlib/v/checker/tests/non_optional_array_append_optional_type_err.vv

@@ -0,0 +1,14 @@
+pub enum Foobar {
+	foo
+	bar
+}
+
+fn get_foo_or_none(fail bool) ?Foobar {
+	return if fail {none} else {.foo}
+}
+
+fn main() {
+	mut foobars := []Foobar{}
+	foobars << ?Foobar(.foo)
+	foobars << get_foo_or_none(true)
+}

vlib/v/checker/tests/option_fn_err.out

@@ -40,6 +40,13 @@ vlib/v/checker/tests/option_fn_err.vv:49:6: error: cannot use `?int` as `int`, i
       |         ~~~~~~
    50 |
    51 |     // array
+vlib/v/checker/tests/option_fn_err.vv:53:6: error: unwrapped Option cannot be used in an infix expression
+   51 |     // array
+   52 |     mut arr := [1, 2]
+   53 |     arr << bar(0)
+      |         ~~
+   54 |     // init
+   55 |     _ := [bar(0)]
 vlib/v/checker/tests/option_fn_err.vv:56:27: error: cannot use unwrapped Option as initializer
    54 |     // init
    55 |     _ := [bar(0)]