[Bug c++/94760] New: coroutines: mismatch between traits and promise parameter preview.

[Bug c++/94760] New: coroutines: mismatch between traits and promise parameter preview.

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94760

            Bug ID: 94760
           Summary: coroutines: mismatch between traits and promise
                    parameter preview.
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iains at gcc dot gnu.org
  Target Milestone: ---

Created attachment 48374
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48374&action=edit
fix under test

There was considerable confusion about how the various implementations
had interpreted the passing of 'this' and lambda capture object
pointers to traits lookup and the promise methods (constructor and
allocator)

In response, we changed the argument passed to the promise parameter
preview to match a reference to *this.  That has made things inconsistent
and we need to match it in the traits

the following code should compile, but fails unable to find a suitable
promise CTOR.

====

struct Fake {} ;

template<typename R, typename CallOp, typename ...T>
struct std::coroutine_traits<R, CallOp, T...> {
    struct promise_type {
        promise_type (CallOp op, T ...args) {}
        Fake get_return_object() { return {}; }
        std::suspend_always initial_suspend() { return {}; }
        std::suspend_never final_suspend() { return {}; }
        void return_void() {}
        void unhandled_exception() {}
    };
};


struct Foo
{
  Fake operator() (int a) {
    co_return;
  }
};

[Bug c++/94760] coroutines: mismatch between traits and promise parameter preview.

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94760

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
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-04-25
   Target Milestone|---                         |10.0
     Ever confirmed|0                           |1

[Bug c++/94760] coroutines: mismatch between traits and promise parameter preview.

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94760

--- Comment #1 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:f5edc76acac7bbadd8d1b00c4cc5994b2a088542

commit r10-8005-gf5edc76acac7bbadd8d1b00c4cc5994b2a088542
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Tue Apr 28 02:15:07 2020 +0100

    coroutines: Pass class ref to traits lookup and promise allocator
[PR94760].

    We changed the argument passed to the promise parameter preview
    to match a reference to *this.  However to be consistent with the
    other ports, we do need to match the reference transformation in
    the traits lookup and the promise allocator lookup.

    gcc/cp/ChangeLog:

    2020-04-28  Iain Sandoe  <iain@sandoe.co.uk>

            PR c++/94760
            * coroutines.cc (instantiate_coro_traits): Pass a reference to
            object type rather than a pointer type for 'this', for method
            coroutines.
            (struct param_info): Add a field to hold that the parm is a lambda
            closure pointer.
            (morph_fn_to_coro): Check for lambda closure pointers in the
            args.  Use a reference to *this when building the args list for the
            promise allocator lookup.

    gcc/testsuite/ChangeLog:

    2020-04-28  Iain Sandoe  <iain@sandoe.co.uk>

            PR c++/94760
            * g++.dg/coroutines/pr94760-mismatched-traits-and-promise-prev.C:
            New test.

[Bug c++/94760] coroutines: mismatch between traits and promise parameter preview.

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94760

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #2 from Iain Sandoe <iains at gcc dot gnu.org> ---
fixed on master