Re: [PATCH] c++: Fix ICE in check_local_shadow with enum [PR95560]

[Marek Polacek <polacek@redhat.com>]

On Thu, Jun 11, 2020 at 03:32:14PM -0400, Jason Merrill wrote:
> On 6/10/20 5:11 PM, Marek Polacek wrote:
> > Another indication that perhaps this warning is emitted too early.  We
> > crash because same_type_p gets a null type: we have an enumerator
> > without a fixed underlying type and finish_enum_value_list hasn't yet
> > run.  So check if the type is null before calling same_type_p.
> 
> Hmm, I wonder why we use NULL_TREE for the type of uninitialized enumerators
> in a template; why not give them integer_type_node temporarily?

That breaks enum22.C:

  template <class T>
  struct A {
    enum e_ : unsigned char { Z_, E_=sizeof(Z_) };
  };

  static_assert ( A<double>::E_ == 1, "E_ should be 1");

If we give 'Z_' a type, it's no longer instantiation-dependent, so sizeof(Z_)
immediately evaluates to 4.  Whereas if it doesn't have a type, in the template
we create a SIZEOF_EXPR and only evaluate when instantiating (to 1).

This sounded like a problem big enough for me not to pursue this any further.
Do you want me to try anything else or is the original patch ok?

Marek