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From: "anders.granlund.0 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/97569] New: Declaring a struct in a field declaration of
 another struct.
Date: Sun, 25 Oct 2020 16:18:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97569

            Bug ID: 97569
           Summary: Declaring a struct in a field declaration of another
                    struct.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anders.granlund.0 at gmail dot com
  Target Milestone: ---

Consider the following c++ program:

  int main()
  {
      struct A
      {
        struct B *b;
      };

      using U =3D B;=20=20=20
  }

Compile it with "-std=3Dc++20 -pedantic-errors".

The gcc compiler accepts it.

Clang however rejects it with the following error=20
message: "unknown type name 'B': using U =3D B;".

The interesting thing is that if we replace  struct S  with  struct S {}  b=
oth
compilers agree on rejecting the program.

I'm not sure if this is a bug in gcc or clang, but I think this is a gcc bu=
g.=