[Bug c++/99710] New: coroutines: co_yield and co_await should only be allowed in suspension context

[Bug c++/99710] New: coroutines: co_yield and co_await should only be allowed in suspension context

[nilsgladitz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99710

            Bug ID: 99710
           Summary: coroutines: co_yield and co_await should only be
                    allowed in suspension context
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nilsgladitz at gmail dot com
  Target Milestone: ---

I quite enjoyed seemingly being able to co_await in exception catch handlers
but as I am being told by another compiler this is apparently not legal.

Not sure I really understand why the standard disallows this but perhaps gcc
should issue a corresponding error diagnostic as well.

Equivalent (fixed) issue report I found for clang:
https://bugs.llvm.org/show_bug.cgi?id=40978

[Bug c++/99710] coroutines: co_yield and co_await should only be allowed in suspension context

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99710

Iain Sandoe <iains at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-09-30
                 CC|                            |iains at gcc dot gnu.org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Iain Sandoe <iains at gcc dot gnu.org> ---
indeed we should reject this

[Bug c++/99710] coroutines: co_yield and co_await should only be allowed in suspension context

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99710

--- Comment #2 from Iain Sandoe <iains at gcc dot gnu.org> ---
#include <coroutine>

struct task {
    struct promise_type {
        std::suspend_always initial_suspend();
        std::suspend_always final_suspend() noexcept;
        task get_return_object();
        void return_void();
        void unhandled_exception();
    };
};

task
my_coro ()
{
  try
    { }
  catch (...)
    {
      // [expr.await]
      co_await std::suspend_always{}; // { dg-error "We should have an error
here" }
    }
}

[Bug c++/99710] coroutines: co_yield and co_await should only be allowed in suspension context

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99710

Iain Sandoe <iains at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |iains at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/99710] coroutines: co_yield and co_await should only be allowed in suspension context

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99710

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Iain D Sandoe <iains@gcc.gnu.org>:

https://gcc.gnu.org/g:650beb110538097b9c3e8600149b333a83e7e836

commit r12-4102-g650beb110538097b9c3e8600149b333a83e7e836
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Sat Oct 2 14:43:39 2021 +0100

    coroutines: Await expressions are not allowed in handlers [PR 99710].

    C++20 [expr.await] / 2
    An await-expression shall appear only in a potentially-evaluated expression
    within the compound-statement of a function-body outside of a handler.

    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

            PR c++/99710

    gcc/cp/ChangeLog:

            * coroutines.cc (await_statement_walker): Report an error if
            an await expression is found in a handler body.

    gcc/testsuite/ChangeLog:

            * g++.dg/coroutines/pr99710.C: New test.