[Bug c++/112632] [14 Regression] Non-type template parameter created with converting constructor sometimes has original type

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112632

--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:5ee5a05da06078975a933be849431eee1d4c6989

commit r16-4211-g5ee5a05da06078975a933be849431eee1d4c6989
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Oct 3 18:10:36 2025 +0100

    c++: concepts and conversions, take 2 [PR122127]

    My r16-4115 changed convert_template_argument (when called from
    instantiate_alias_template) to take the maybe_convert_nontype_argument path
    rather than convert_nontype_argument for this testcase.  This meant not
    folding the use of the by-ref capture in the template argument to constant
    1.  When we come back to convert_template_argument again when substituting
    into resize<_Np> we strip the IMPLICIT_CONV_EXPR (since the types are the
    same) and take the convert_nontype_argument path, but at this point we've
    pushed into the alias template context and trying to fold away the capture
    fails because current_lambda_expr() is now null.

    Taking the convert_nontype_argument path in the same-type case where we
    would later strip an IMPLICIT_CONV_EXPR fixes the problem.  Note that
    maybe_convert_nontype_argument already shares the same-type check with the
    stripping, but that isn't enough; it still doesn't fold away the capture
    proxy.

            PR c++/122127
            PR c++/112632

    gcc/cp/ChangeLog:

            * pt.cc (convert_template_argument): Don't add redundant
            IMPLICIT_CONV_EXPR.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/lambda/lambda-template18.C: New test.