[Bug c++/92402] parsing error in lambda trail return type with decltype, statement expressions and structured bindings

2020-01-30 Thread mpolacek at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92402

--- Comment #4 from Marek Polacek  ---
Not a regression though, so I'll leave it for GCC 11.

[Bug c++/92402] parsing error in lambda trail return type with decltype, statement expressions and structured bindings

2020-01-30 Thread mpolacek at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92402

--- Comment #3 from Marek Polacek  ---
Even shorter:

int a[1];
void f() {
  []() -> decltype(({auto&& [x] = a; 0;})) { return 0; };
}

clang++ compiles it.

[Bug c++/92402] parsing error in lambda trail return type with decltype, statement expressions and structured bindings

2020-01-30 Thread marxin at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92402

Martin Liška  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2020-01-30
 CC||jason at gcc dot gnu.org,
   ||marxin at gcc dot gnu.org,
   ||mpolacek at gcc dot gnu.org
 Ever confirmed|0   |1

--- Comment #2 from Martin Liška  ---
Confirmed.

[Bug c++/92402] parsing error in lambda trail return type with decltype, statement expressions and structured bindings

2019-11-21 Thread wjwray at gmail dot com 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92402

Will Wray  changed:

   What|Removed |Added

 CC||wjwray at gmail dot com

--- Comment #1 from Will Wray  ---
Here's a motivating use case; https://godbolt.org/z/Tt-QmN
This allows to effectively SFINAE on structured binding - a 'missing link'.
Works in Clang since 5.0.

GDB debugging gcc latest trunk build. The parse error occurs here

gcc/cp/parser.c:13869

 cp_parser_decomposition_declaration

  else if (decl != error_mark_node && DECL_CHAIN (decl2) != prev)
{
  /* Ensure we've diagnosed redeclaration if we aren't creating
 a new VAR_DECL.  */
  gcc_assert (errorcount);  /*** HERE  ***/
  decl = error_mark_node;
}

Haven't worked out exactly what is being checked there.

So I tried commenting out that entire else-if block to see what happens.
It then proceeds to mangling and crashes out in contains_struct_check.
Backtrace looks like this:

#0  contains_struct_check gcc/cp/mangle.c "write_closure_type_name"
gcc/tree.h:3386
#1  write_closure_type_name gcc/cp/mangle.c:1641 in write_unqualified_name 
#3  write_prefix gcc/cp/mangle.c:1164 in mangle_decomp  at gcc/cp/mangle.c:4050
#5  cp_maybe_mangle_decomp gcc/cp/decl.c:8024
#6  cp_parser_decomposition_declaration