v.ast: allow for fn f()&IAbc{return voidptr(0)} with no additional …

…voidptr implicit conversions to compile

vlib/v/ast/table.v

@@ -1122,6 +1122,9 @@ fn (mut table Table) does_type_implement_interface(typ Type, inter_typ Type) boo
 			return false
 		}
 		inter_sym.info.types << utyp
+		if !inter_sym.info.types.contains(voidptr_type) {
+			inter_sym.info.types << voidptr_type
+		}
 	}
 	return true
 }

vlib/v/tests/interface_edge_cases/fn_returning_voidptr_casted_as_interface_test.v

@@ -0,0 +1,24 @@
+interface IAbc {
+	name string
+	xyz()
+}
+
+fn f(i &IAbc) string {
+	return '$i'
+}
+
+struct Abc {
+	name string
+	x    int = 123
+}
+
+fn (a Abc) xyz() {}
+
+fn resource__null() &IAbc {
+	return voidptr(0)
+}
+
+fn test_fn_returning_voidptr_casted_as_interface_works() {
+	pi := resource__null()
+	assert f(pi) == '&IAbc(0)'
+}