[Bug c++/66439] Diagnostic on failed function template lookup is missing a line

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66439

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>:

https://gcc.gnu.org/g:864fed4a491606a7b17325d847e1d723d2a44104

commit r11-476-g864fed4a491606a7b17325d847e1d723d2a44104
Author: Patrick Palka <ppa...@redhat.com>
Date:   Mon May 18 23:50:14 2020 -0400

    c++: Explain fn template argument type/value mismatches [PR66439]

    In fn_type_unifcation, we are passing NULL_TREE as the 'in_decl'
    parameter to coerce_template_parms, and this is causing template
    type/value mismatch error messages to get suppressed regardless of the
    value of 'complain'.

    This means that when substitution into a function template fails due to
    a type/value mismatch between a template parameter and the provided
    template argument, we just say "template argument deduction/substitution
    failed:" without a followup explanation of the failure.

    Fix this by passing 'fn' instead of NULL_TREE to coerce_template_parms.

    gcc/cp/ChangeLog:

            PR c++/66439
            * pt.c (fn_type_unification): Pass 'fn' instead of NULL_TREE as
            the 'in_decl' parameter to coerce_template_parms.

    gcc/testsuite/ChangeLog:

            PR c++/66439
            * g++.dg/cpp2a/concepts-ts4.C: Expect a "type/value mismatch"
            diagnostic.
            * g++.dg/cpp2a/concepts-ts6.C: Likewise.
            * g++.dg/template/error56.C: Likewise.
            * g++.dg/template/error59.C: New test.

    libstdc++-v3/ChangeLog:

            PR c++/66439
            * testsuite/20_util/pair/astuple/get_neg.cc: Prune "type/value
            mismatch" messages.
            * testsuite/20_util/tuple/element_access/get_neg.cc: Likewise.