On Fri, 20 Sep 2024, Jason Merrill wrote:
> On 9/20/24 6:51 PM, Patrick Palka wrote:
> > On Fri, 20 Sep 2024, Jason Merrill wrote:
> >
> > > On 9/18/24 10:59 PM, Patrick Palka wrote:
> > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this
> > > > look OK for trunk? I'm not sure this is worth backporting
> > > > without the previous CWG 2273 tweak since it'll mean inconsistent
> > > > behavior between implict vs explicit object members in GCC 14: the call
> > > > to S<>{}.f() in concepts-memfun4.C would now return 10 (due to the CWG
> > > > 2273 tiebreaker incorrectly triggering), while the g() and h() calls
> > > > would be ambiguous (since that tiebreaker doesn't consider object
> > > > correspondence).
> > >
> > > Agreed, I wouldn't backport.
> >
> > What do you think about enforcing this part of CWG 2789 only for
> > constructors in GCC 14? That would sidestep the inconsistency that
> > arises if we don't also backport the CWG 2273, and still fix the
> > testcase in the PR.
> >
> > Like so?
>
> That seems reasonable with a comment.
Ack, does
/* This really really be checked for all member functions as per
CWG2789, but for GCC 14 we check this only for constructors since
without r15-3740 doing so would result in inconsistent handling
of object parameters (such as in concepts-memfun4.C). */
work?
>
> > -- >8 --
> >
> > Subject: [PATCH GCC 14] c++: CWG 2789 and usings [PR116492]
> >
> > For GCC 14, narrowly fix this PR by enforcing the unimplemented
> >
> > - if they are member functions, both are direct members of the same
> > class, and
> >
> > part of CWG 2789 for constructors only.
> >
> > PR c++/116492
> > DR 2789
> >
> > gcc/cp/ChangeLog:
> >
> > * call.cc (cand_parms_match): Return false for constructors that
> > come from different classes.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp2a/concepts-inherit-ctor12.C: New test.
> > ---
> > gcc/cp/call.cc | 4 ++++
> > .../g++.dg/cpp2a/concepts-inherit-ctor12.C | 16 ++++++++++++++++
> > 2 files changed, 20 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
> >
> > diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
> > index 0f4eeeb5395..5c7aaa6dcf1 100644
> > --- a/gcc/cp/call.cc
> > +++ b/gcc/cp/call.cc
> > @@ -12826,6 +12826,10 @@ cand_parms_match (z_candidate *c1, z_candidate *c2,
> > pmatch match_kind)
> > && DECL_FUNCTION_MEMBER_P (fn2)))
> > /* Early escape. */;
> > + else if ((DECL_INHERITED_CTOR (fn1) || DECL_INHERITED_CTOR (fn2))
> > + && (DECL_CONTEXT (strip_inheriting_ctors (fn1))
> > + != DECL_CONTEXT (strip_inheriting_ctors (fn2))))
> > + return false;
> > /* CWG2789 is not adequate, it should specify corresponding object
> > parameters, not same typed object parameters. */
> > else if (!object_parms_correspond (c1, fn1, c2, fn2))
> > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
> > b/gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
> > new file mode 100644
> > index 00000000000..3e5dbfc37ad
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
> > @@ -0,0 +1,16 @@
> > +// PR c++/116492
> > +// CWG 2789
> > +// { dg-do compile { target c++20 } }
> > +
> > +template<class T>
> > +struct A {
> > + A() requires true = delete;
> > +};
> > +
> > +struct B : A<int> {
> > + B();
> > + using A<int>::A;
> > +};
> > +
> > +B b; // OK, selects the non-inherited constructor over the more constrained
> > + // inherited constructor.
>
>
