Bug 14632 – Diagnostic improvement for invalid cast with alias this

Spin-off from issue 14093. From dmd test suite test/fail_compilation/fail_casting.d: /* TEST_OUTPUT: --- fail_compilation/fail_casting.d(179): Error: cannot cast expression __tup$n$.__expand_field_0 of type int to object.Object fail_compilation/fail_casting.d(179): Error: cannot cast expression __tup$n$.__expand_field_1 of type int to object.Object --- */ alias TypeTuple14093(T...) = T; struct Tuple14093(T...) { static if (T.length == 4) { alias Types = TypeTuple14093!(T[0], T[2]); Types expand; @property ref inout(Tuple14093!Types) _Tuple_super() inout @trusted { return *cast(typeof(return)*) &(expand[0]); } alias _Tuple_super this; } else { alias Types = T; Types expand; alias expand this; } } void test14093() { Tuple14093!(int, "x", int, "y") point; auto newPoint = cast(Object)(point); // line 179 } The message can be better as follows: Error: cannot cast expression point of type Tuple14093!(int, "x", int, "y") to object.Object

Reduced: struct Tuple(T...) { alias Types = T; Types expand; alias expand this; } void test() { Tuple!(int, int) point; auto newPoint = cast(Object)(point); } Error messages no longer use '__tup$n$' but could still be improved as per comment 0: onlineapp.d(10): Error: cannot cast expression point.__expand_field_0 of type int to object.Object onlineapp.d(10): Error: cannot cast expression point.__expand_field_1 of type int to object.Object

Commit pushed to master at https://github.com/dlang/dmd https://github.com/dlang/dmd/commit/4d4cd923df4401cf4aef4744c5c122adf8aeb631 Fix Issue 6777 and 14632 - alias this disables casting for classes