[Bug c++/98617] New: Failure to recognize pack expansion argument for non-pack parameter of alias template when alias is "exact"

[ryan_greenblatt at brown dot edu via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98617

            Bug ID: 98617
           Summary: Failure to recognize pack expansion argument for
                    non-pack parameter of alias template when alias is
                    "exact"
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ryan_greenblatt at brown dot edu
  Target Milestone: ---

It is invalid to expand a parameter pack into a non pack parameter of an alias
template. However, gcc accepts this when the alias is exactly the same as the
struct it is aliasing.

Consider https://godbolt.org/z/YrqTTx

AliasA doesn't fail, but it should fail with the same error as AliasB and
AliasC.