checker: disallow voidptr cast to struct (#18845)

vlib/term/ui/README.md

@@ -19,7 +19,7 @@ fn event(e &tui.Event, x voidptr) {
 }
 
 fn frame(x voidptr) {
-	mut app := &App(x)
+	mut app := unsafe { &App(x) }
 
 	app.tui.clear()
 	app.tui.set_bg_color(r: 63, g: 81, b: 181)

vlib/v/checker/checker.v

@@ -2943,9 +2943,9 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 				else {}
 			}
 		}
-		if from_type == ast.voidptr_type_idx && !c.inside_unsafe {
-			// TODO make this an error
-			c.warn('cannot cast voidptr to a struct outside `unsafe`', node.pos)
+		if from_type == ast.voidptr_type_idx && !c.inside_unsafe && !c.pref.translated
+			&& !c.file.is_translated {
+			c.error('cannot cast voidptr to a struct outside `unsafe`', node.pos)
 		}
 		if !from_type.is_int() && final_from_sym.kind != .enum_
 			&& !from_type.is_any_kind_of_pointer() {

vlib/v/checker/tests/voidptr_cast_to_struct_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/voidptr_cast_to_struct_err.vv:4:7: error: cannot cast `voidptr` to struct
+    2 | 
+    3 | fn main() {
+    4 |     a := Foo(unsafe { nil })
+      |          ~~~~~~~~~~~~~~~~~~~
+    5 |     println(a)
+    6 | }

vlib/v/checker/tests/voidptr_cast_to_struct_err.vv

@@ -0,0 +1,6 @@
+struct Foo {}
+
+fn main() {
+	a := Foo(unsafe { nil })
+	println(a)
+}

vlib/v/tests/option_generic_ptr_return_test.v

@@ -8,7 +8,7 @@ struct ABCD {}
 pub fn cast_object_desc[H](desc &ObjectDesc) ?H {
 	$if H is &ABCD {
 		if desc.typ == 12 { // desc == ABCD
-			return &ABCD(desc.ptr)
+			return unsafe { &ABCD(desc.ptr) }
 		}
 	}
 	return none

vlib/v/tests/option_ptr_cast_test.v

@@ -14,7 +14,7 @@ pub fn cast_object_desc[H](desc &ObjectDesc) ?H {
 			return &ABCD(desc.ptr)
 		}*/
 		if desc.typ == 12 { // desc == ABCD
-			return ?&ABCD(&ABCD(desc.ptr))
+			return ?&ABCD(unsafe { &ABCD(desc.ptr) })
 		}
 	}
 	return none

vlib/v/tests/pointers_multilevel_casts_test.v

@@ -49,10 +49,10 @@ fn test_struct_pointer_casts_with_field_selectors() {
 	}
 	dump(ss)
 	pss := voidptr(ss)
-	if &Struct(pss).name == 'abc' {
+	if unsafe { &Struct(pss).name } == 'abc' {
 		assert true
 	}
-	if &Struct(pss).x == 123 {
+	if unsafe { &Struct(pss).x } == 123 {
 		// &Struct cast and selecting .x
 		assert true
 	}