From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTP id 881C43857809 for ; Mon, 17 May 2021 14:25:52 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 881C43857809 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-578-eDMsOPgJPe6AvfoYms4Euw-1; Mon, 17 May 2021 10:25:50 -0400 X-MC-Unique: eDMsOPgJPe6AvfoYms4Euw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 873059126F; Mon, 17 May 2021 14:25:49 +0000 (UTC) Received: from localhost (unknown [10.33.36.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2356910027C4; Mon, 17 May 2021 14:25:48 +0000 (UTC) Date: Mon, 17 May 2021 15:25:48 +0100 From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: Re: [PATCH] libstdc++: Fix filesystem::path constraints for volatile [PR 100630] Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-Clacks-Overhead: GNU Terry Pratchett X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline X-Spam-Status: No, score=-8.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libstdc++@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++ mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 17 May 2021 14:25:59 -0000 On 17/05/21 15:02 +0100, Jonathan Wakely wrote: >The constraint check for filesystem::path construction uses >decltype(__is_path_src(declval())) which mean it considers >conversion from an rvalue. When Source is a volatile-qualified type >it cannot use is_path_src(const Unknown&) because a const lvalue >reference can only bind to a non-volatile rvalue. > >Since the relevant path members all have a const Source& parameter, >the constraint should be defined in terms of declval(), >not declval(). This avoids the problem of volatile-qualified >rvalues, because we no longer use an rvalue at all. > >libstdc++-v3/ChangeLog: > > PR libstdc++/100630 > * include/bits/fs_path.h (__is_constructible_from): Test > construction from a const lvalue, not an rvalue. > * include/experimental/bits/fs_path.h (__is_constructible_from): > Likewise. > * testsuite/27_io/filesystem/path/construct/100630.cc: New test. > * testsuite/experimental/filesystem/path/construct/100630.cc: > New test. > >Tested x86_64-linux, pushed to gcc-10 (this isn't needed for gcc-11 or >trunk, but I also plan to backport it to gcc-9). Oh actually this is needed for experimental::filesystem::path on trun kand gcc-11 (as I found when I added to the new tests to trunk) so I'll fix it there too.