[nv-cmeerw]

With the changes for EDGcpfe/28857 (in version 6.9), a decltype in an alias
template that deduces class template arguments through one of the alias
template's template template parameters could trigger an internal error due to
a failed assertion in generic_cast_operand, when the alias was used with
dependent arguments, for example in a requires expression. For example, with
--c++20:

  template<typename T> struct S { S(T); };
  template<template<typename> class TT> using A = decltype(TT(0));
  template<template<typename> class TT>
  constexpr bool b = requires { typename A<TT>; };
  static_assert(b<S>);  // Previously an internal error, now okay.

In addition, deduction now succeeds when the template bound to the template
template parameter has more parameters (with default arguments or packs) than
the parameter itself, and a mismatch is now treated as a deduction failure
rather than an error in contexts where errors are not issued.

[nv-cmeerw]

@stevensudit-corvid FYI

[daveedvdv-nvidia]

Just suggestions for more comments.

[daveedvdv-nvidia]

Looks great.