[Bug c++/96184] New: GCC treats "use of local variable with automatic storage from containing function" differently in versions

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96184

            Bug ID: 96184
           Summary: GCC treats "use of local variable with automatic
                    storage from containing function" differently in
                    versions
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          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, GCC-trunk and other versions (etc., GCC-10) treat it differently.

$cat test.cc
int main(){
    int a  = 10;
    int const b = 10;
    auto p = [ ] () noexcept ( b ? 0 : a = b) { return 0;};
    return 0;
}

$g++-trunk -std=c++14 test.cc
//nothing

$g++-10 -std=c++14 test.cc
test.cc: In function ‘int main()’:
test.cc:4:40: error: use of local variable with automatic storage from
containing function
    4 |     auto p = [ ] () noexcept ( b ? 0 : a = b) { return 0;};
      |                                        ^
test.cc:2:9: note: ‘int a’ declared here
    2 |     int a  = 10;
      |         ^

I am wondering is this a enhancement of GCC-trunk? 

I also test this in other GCC versions. Weirdly, only GCC-9 or GCC-10 rejects
it while other versions from 6.1 to 8.3 (also trunk) accepts it.

I don't know how GCC deals with this case and this also makes me confused.

Thanks,
Haoxin