checker: forbid optional variable (#14460)

vlib/v/checker/checker.v

@@ -2312,6 +2312,10 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 	mut to_sym := c.table.sym(to_type) // type to be used as cast
 	mut final_to_sym := c.table.final_sym(to_type)
 
+	if to_type.has_flag(.optional) {
+		c.error('casting to optional type is forbidden', node.pos)
+	}
+
 	if (to_sym.is_number() && from_sym.name == 'JS.Number')
 		|| (to_sym.is_number() && from_sym.name == 'JS.BigInt')
 		|| (to_sym.is_string() && from_sym.name == 'JS.String')

vlib/v/checker/tests/optional_variable_err.out

@@ -0,0 +1,5 @@
+vlib/v/checker/tests/optional_variable_err.vv:2:7: error: casting to optional type is forbidden
+    1 | fn main() {
+    2 |     _ := ?bool(false)
+      |          ~~~~~~~~~~~~
+    3 | }

vlib/v/checker/tests/optional_variable_err.vv

@@ -0,0 +1,3 @@
+fn main() {
+	_ := ?bool(false)
+}

vlib/v/gen/c/cgen.v

@@ -2243,10 +2243,6 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 			g.write('*')
 		}
 	}
-	if expected_type.has_flag(.optional) && expr is ast.None {
-		g.gen_optional_error(expected_type, expr)
-		return
-	}
 	if expr is ast.IntegerLiteral {
 		if expected_type in [ast.u64_type, ast.u32_type, ast.u16_type] && expr.val[0] != `-` {
 			g.expr(expr)

vlib/v/tests/optional_assign_test.v

@@ -1,25 +0,0 @@
-type Foo = int | string
-
-fn test_optional_none_assign() {
-	x := ?Foo(none)
-	// assert x.err == none
-	// assert !x.has_value
-}
-
-fn test_optional_none_assign_nonsumtype() {
-	x := ?int(none)
-	// assert x.err == none
-	// assert !x.has_value
-}
-
-// TODO: make this working next
-/*
-fn test_optional_value_assign() {
-	x := ?Foo('test')
-}
-
-fn test_optional_none_reassign() {
-	mut x := ?Foo('test')
-	x = none
-}
-*/