[Bug c++/124794] [reflection] ICE on member function template splicing

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124794

--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-16 branch has been updated by Marek Polacek
<[email protected]>:

https://gcc.gnu.org/g:4a459598063f4a7867aa142e9e1bf49479b91c13

commit r16-9572-g4a459598063f4a7867aa142e9e1bf49479b91c13
Author: Marek Polacek <[email protected]>
Date:   Fri Jul 31 11:57:14 2026 -0400

    c++/reflection: ICE with &template [:members_of():] [PR124794]

    Given

      struct C { template <class T> void f(T); };

    we handle "&template [:^^C::f:]" correctly because the spliced
    expression is

      BASELINK<OVERLOAD<TEMPLATE_DECL f>>, binfo C>

    which is fine: we have an OVERLOAD around the TEMPLATE_DECL and
    lookup_member wrapped the whole thing in a BASELINK.  But when
    we're splicing members_of(^^C, ac)[0], we ended up with

      OVERLOAD<TEMPLATE_DECL f>>

    and then go down the wrong path in cp_parser_splice_expression.

    splice already correctly adds the missing OVERLOAD but it also
    needs to (maybe) add a BASELINK.

    This patch also adjusts baselink_for_fns to gain a parameter
    controlling if we want to ignore currently_open_derived_class.
    It matters when we're in a member function of a class derived
    from C and the object argument of the -> is a different derived class,
    as exercised in splice17.C: pd->[:g1:] (42); in D2::mfn.  There, if
    we didn't ignore currently_open_derived_class, the BASELINK would
    use D2 as the access_binfo, which is wrong because it has no
    derivation relationship to the object type (here D1).  With this
    patch access_binfo will be C, which is what members_of gave us.

            PR c++/124794

    gcc/cp/ChangeLog:

            * cp-tree.h (baselink_for_fns): Adjust declaration.
            * parser.cc (cp_parser_reflect_expression): Adjust the call to
            baselink_for_fns.
            * reflect.cc (splice): Call baselink_for_fns.
            * semantics.cc (baselink_for_fns): Add a bool parameter.  If
            it's true, ignore currently_open_derived_class.

    gcc/testsuite/ChangeLog:

            * g++.dg/reflect/splice17.C: New test.

    Reviewed-by: Jason Merrill <[email protected]>
    (cherry picked from commit 8fb57eda04f88f4e0d1cbbcc209533fd9689dd9d)