[Bug c++/97010] C++20 ADL and function templates that are not visible (P0846R0) fails on call with templated type

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97010

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

https://gcc.gnu.org/g:635072248a426c933c74ef4431e82401249b6218

commit r11-3709-g635072248a426c933c74ef4431e82401249b6218
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Sep 10 17:27:43 2020 -0400

    c++: Fix P0846 (ADL and function templates) in template [PR97010]

    To quickly recap, P0846 says that a name is also considered to refer to
    a template if it is an unqualified-id followed by a < and name lookup
    finds either one or more functions or finds nothing.

    In a template, when parsing a function call that has type-dependent
    arguments, we can't perform ADL right away so we set KOENIG_LOOKUP_P in
    the call to remember to do it when instantiating the call
    (tsubst_copy_and_build/CALL_EXPR).  When the called function is a
    function template, we represent the call with a TEMPLATE_ID_EXPR;
    usually the operand is an OVERLOAD.

    In the P0846 case though, the operand can be an IDENTIFIER_NODE, when
    name lookup found nothing when parsing the template name.  But we
    weren't handling this correctly in tsubst_copy_and_build.  First
    we need to pass the FUNCTION_P argument from <case TEMPLATE_ID_EXPR> to
    <case IDENTIFIER_NODE>, otherwise we give a bogus error.  And then in
    <case CALL_EXPR> we need to perform ADL.  The rest of the changes is to
    give better errors when ADL didn't find anything.

    gcc/cp/ChangeLog:

            PR c++/97010
            * pt.c (tsubst_copy_and_build) <case TEMPLATE_ID_EXPR>: Call
            tsubst_copy_and_build explicitly instead of using the RECUR macro.
            Handle a TEMPLATE_ID_EXPR with an IDENTIFIER_NODE as its operand.
            <case CALL_EXPR>: Perform ADL for a TEMPLATE_ID_EXPR with an
            IDENTIFIER_NODE as its operand.

    gcc/testsuite/ChangeLog:

            PR c++/97010
            * g++.dg/cpp2a/fn-template21.C: New test.
            * g++.dg/cpp2a/fn-template22.C: New test.