[Bug c++/90101] New: [P0732]

[mateusz.pusz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90101

            Bug ID: 90101
           Summary: [P0732]
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mateusz.pusz at gmail dot com
  Target Milestone: ---

Hi,

Compiling the code provided below with the following options produces an error:
"-std=c++2a -Wall -Wextra"

```
template<typename List>
struct A;

template<template<auto...> typename List>
struct A<List<>> {};

template<template<auto...> typename List, auto V>
struct A<List<V>> {};

template<auto>
struct B {};

// works
A<B<1>> a1;

// error
struct X {
    int value;
};
A<B<X{1}>> a2;
```

Error:
<source>:20:12: error: aggregate 'A<B<X{1}> > a2' has incomplete type and
cannot be defined
   20 | A<B<X{1}>> a2;
      |            ^~

See also: https://godbolt.org/z/QSRjFb

Best

Mat