[Bug c++/113919] New: Nested anonymous unions should be prohibited in ISO C++

[tsqurt at outlook dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113919

            Bug ID: 113919
           Summary: Nested anonymous unions should be prohibited in ISO
                    C++
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tsqurt at outlook dot com
  Target Milestone: ---

Created attachment 57425
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57425&action=edit
example.cpp

Anonymous unions shall not be declared within an anonymous union. But gcc never
warns about this. 

Demo source code as a C++17 source file attached. Note: attached code is a
valid C 
source code but not a valid C++ source code. GCC is expected to REJECT or WARN,
but it compiles without any message.

$gcc example.cpp -std=c++17 --pedantic -Wall -Wextra

expect:
warning: ISO C++ prohibits anonymous unions within anonymous unions[-Wpedantic]

But gcc exited with code 0, leaving empty message.

Reference: N4849, Working Draft, Standard for Programming Language C++, Chapter
11, Section 5.1 Anonymous unions. (Different versions of modern C++
specification mention this issue in their correspondent chapters.)