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[2001:8b0:bf73:93f7::51bb:e332]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c5c11fe22sm3024073f8f.41.2025.01.30.14.07.04 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jan 2025 14:07:05 -0800 (PST) Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.97) (envelope-from ) id 1tdcgg-0000000HR1L-2y16 for sc22wg14@open-std.org; Thu, 30 Jan 2025 22:07:02 +0000 Date: Thu, 30 Jan 2025 22:07:02 +0000 (UTC) From: Joseph Myers To: sc22wg14@open-std.org Subject: N3420 lvalue conversion of incomplete types Message-ID: <43505ab9-c992-a3bd-2504-6d53cda3de0f@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: MvsGz_8hxqvGpS269EFknX0SR0bhVttXCHT4JhXuTgY_1738274827 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Sender: owner-sc22wg14@open-std.org Precedence: bulk N3420 proposes replacing undefined behavior for lvalue conversion of an incomplete type (other than void, since lvalues can't have type void) with a constraint violation. 1. I see my previous reversion of changes incorrectly applied from N3244 item 19 was incomplete. I've now filed https://gitlab.gwdg.de/iso-c/draft/-/merge_requests/513 to restore the sentence that N3420 would remove so that we can consider the change on the basis of a current working draft. Could the editors please review the 36 open merge requests (preferably also issue 442 for a missing paper) so that we can get a new working draft issued before Graz that more accurately reflects what has and hasn't been approved so far for C2y and can be used as a basis for future work in Graz? 2. The proposed changes seem to make the constraint only apply where the "expression" syntax production is used - not in any case going through one of the other syntax productions for a particular kind of expression but not through "expression" itself. For example, the LHS of a comma-expression would, after these changes, never go through the expression syntax production, so not be subject to the constraint (although it would be subject to the present UB). Likewise if the lvalue with incomplete type is cast to void. (In the case of an unselected generic association, the correct handling is a bit less clear. The selected generic association can be used in a context where no lvalue conversion takes place, so what does that mean regarding constraints for lvalue conversion as applied to unselected generic associations, and does that depend at all on the context in which _Generic is used?) -- Joseph S. Myers josmyers@redhat.com