struct A { int a; }; struct A { int a; }; is rejected by clang -std=c23

[pascal-cuoq]

I have read #149965 but this seems like a different issue.

I understand that the program struct A { int a; }; struct A { int a; }; is valid C23. GCC 15.2 accepts it with -std=c23 and rejects it with -std=c17. It is rejected by Clang 20.1.0 with -std=c23:

<source>:5:8: error: redefinition of 'A'
    5 | struct A { int a; };
      |        ^
<source>:3:8: note: previous definition is here
    3 | struct A { int a; };
      |        ^
1 error generated.
Compiler returned: 1

CE link: https://gcc.godbolt.org/z/Ej7vzY4z5

[frederick-vs-ja]

This feature is implemented in Clang 21 (see #132939).

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Pascal Cuoq (pascal-cuoq)

I have read https://github.com//issues/149965 but this seems like a different issue.

I understand that the program struct A { int a; }; struct A { int a; }; is valid C23. GCC 15.2 accepts it with -std=c23 and rejects it with -std=c17. It is rejected by Clang 20.1.0 with -std=c23:

<source>:5:8: error: redefinition of 'A'
    5 | struct A { int a; };
      |        ^
<source>:3:8: note: previous definition is here
    3 | struct A { int a; };
      |        ^
1 error generated.
Compiler returned: 1

CE link: https://gcc.godbolt.org/z/Ej7vzY4z5

[AaronBallman]

Closing, this was implemented for Clang 21.x by a4ceac7 and numerous follow-ups