From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 083173985445; Wed, 23 Jun 2021 12:25:33 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 083173985445 From: "cvs-commit at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/86439] CTAD with deleted copy constructor fails due to deduction-guide taking by value Date: Wed, 23 Jun 2021 12:25:33 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Version: 8.1.1 X-Bugzilla-Keywords: rejects-valid X-Bugzilla-Severity: normal X-Bugzilla-Who: cvs-commit at gcc dot gnu.org X-Bugzilla-Status: ASSIGNED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: ppalka at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Jun 2021 12:25:34 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D86439 --- Comment #2 from CVS Commits --- The master branch has been updated by Patrick Palka : https://gcc.gnu.org/g:3eecc1db4c691a87ef4a229d059aa863066d9a1c commit r12-1744-g3eecc1db4c691a87ef4a229d059aa863066d9a1c Author: Patrick Palka Date: Wed Jun 23 08:24:34 2021 -0400 c++: CTAD and deduction guide selection [PR86439] During CTAD, we select the best viable deduction guide using build_new_function_call, which performs overload resolution on the set of candidate guides and then forms a call to the guide. As the PR points out, this latter step is unnecessary and occasionally incorrect since a call to the selected guide may be ill-formed, or forming the call may have side effects such as prematurely deducing the type of a {= }. So this patch introduces a specialized subroutine based on build_new_function_call that stops short of building a call to the selected function, and makes do_class_deduction use this subroutine instead. And since a call is no longer built, do_class_deduction doesn't need to set tf_decltype or cp_unevaluated_operand anymore. This change causes us to reject some container CTAD examples in the libstdc++ testsuite due to deduction failure for {}, which AFAICT is the correct behavior. Previously in e.g. the first removed example std::map{{std::pair{1, 2.0}, {2, 3.0}, {3, 4.0}}, {}}, the type of the {} would get deduced to less as a side effect of forming a call to the chosen guide template, typename _Allocator =3D allocator>> map(initializer_list>, _Compare =3D _Compare(), _Allocator =3D _Allocator()) -> map<_Key, _Tp, _Compare, _Allocator>; which made later overload resolution for the constructor call unambiguous. Now, the type of the {} remains undeduced until constructor overload resolution, and we complain about ambiguity for the two equally good constructor candidates map(initializer_list, const _Compare& =3D _Compare(), const allocator_type& =3D allocator_type()) map(initializer_list, const allocator_type&). This patch fixes these problematic container CTAD examples by giving the {} an appropriate concrete type. Two of these adjusted CTAD examples (one for std::set and one for std::multiset) end up triggering an unrelated CTAD bug on trunk, PR101174, so these two adjusted examples are commented out for now. PR c++/86439 gcc/cp/ChangeLog: * call.c (print_error_for_call_failure): Constify 'args' parame= ter. (perform_dguide_overload_resolution): Define. * cp-tree.h: (perform_dguide_overload_resolution): Declare. * pt.c (do_class_deduction): Use perform_dguide_overload_resolu= tion instead of build_new_function_call. Don't use tf_decltype or set cp_unevaluated_operand. Remove unnecessary NULL_TREE tests. libstdc++-v3/ChangeLog: * testsuite/23_containers/map/cons/deduction.cc: Replace ambigu= ous CTAD examples. * testsuite/23_containers/multimap/cons/deduction.cc: Likewise. * testsuite/23_containers/multiset/cons/deduction.cc: Likewise. Mention one of the replaced examples is broken due to PR101174. * testsuite/23_containers/set/cons/deduction.cc: Likewise. * testsuite/23_containers/unordered_map/cons/deduction.cc: Repl= ace ambiguous CTAD examples. * testsuite/23_containers/unordered_multimap/cons/deduction.cc: Likewise. * testsuite/23_containers/unordered_multiset/cons/deduction.cc: Likewise. * testsuite/23_containers/unordered_set/cons/deduction.cc: Likewise. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/class-deduction88.C: New test. * g++.dg/cpp1z/class-deduction89.C: New test. * g++.dg/cpp1z/class-deduction90.C: New test.=