[Bug c++/96120] New: Ambiguity diagnostic message of "invalid use of type 'void' in parameter declaration"

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96120

            Bug ID: 96120
           Summary: Ambiguity diagnostic message of "invalid use of type
                    'void' in parameter declaration"
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haoxintu at gmail dot com
  Target Milestone: ---

Hi, all.

This code, test.cc, GCC might emit the ambiguity diagnostic message on it.

$cat test.cc
void foo1 (void) {}
void foo2 (void, int){}

$g++ -c test.cc
test.cc:2:12: error: invalid use of type ‘void’ in parameter declaration
    2 | void foo2 (void, int){}
      |            ^~~~

Apparently, "void" can be used in parameter declaration like line 1, but GCC
emits the ambiguity message on it. The output information conflicts with valid
grammar, so I guess users might be confused with this diagnostic.

I think clang handles better in this case

$clang++ -c test.cc
test.cc:2:11: error: 'void' must be the first and only parameter if specified
void foo2 (void, int){}
          ^
1 error generated.

Thanks,
Haoxin