From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp66.ord1d.emailsrvr.com (smtp66.ord1d.emailsrvr.com [184.106.54.66]) by sourceware.org (Postfix) with ESMTPS id 1879D3858D28 for ; Wed, 20 Jul 2022 16:47:45 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 1879D3858D28 X-Auth-ID: tom@honermann.net Received: by smtp9.relay.ord1d.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 62918C00EA; Wed, 20 Jul 2022 12:47:44 -0400 (EDT) Message-ID: <6cf42820-86cb-f3ee-e4cf-3310de2e0bd1@honermann.net> Date: Wed, 20 Jul 2022 12:47:43 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH v4 2/3] stdlib: Implement mbrtoc8(), c8rtomb(), and the char8_t typedef. Content-Language: en-US To: Joseph Myers , Adhemerval Zanella Cc: libc-alpha@sourceware.org References: <20220630125215.6052-1-tom@honermann.net> <20220630125215.6052-3-tom@honermann.net> From: Tom Honermann In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Classification-ID: 5af2e61d-c5a9-475f-97fb-5da3082df03b-1-1 X-Spam-Status: No, score=-3.1 required=5.0 tests=BAYES_00, BODY_8BITS, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 20 Jul 2022 16:47:46 -0000 Confirmed that this issue can be easily reproduced outside the testsuite. $ cat t.cpp #include $ g++ --version g++ (GCC) 13.0.0 20220720 (experimental) ... $ g++ -c -I/path/to/glibc-char8_t/include -std=c++17 -Werror=c++20-compat t.cpp In file included from t.cpp:1: /home/tom/products/glibc-char8_t/include/uchar.h:38:23: error: identifier ‘char8_t’ is a keyword in C++20 [-Werror=c++20-compat]    38 | typedef unsigned char char8_t;       |                       ^~~~~~~ cc1plus: some warnings being treated as errors The char8_t typedef is currently guarded by: /* Declare the C2x char8_t typedef in C2x modes, but only if the C++   __cpp_char8_t feature test macro is not defined.  */ #if __GLIBC_USE (ISOC2X) && !defined __cpp_char8_t /* Define the 8-bit character type.  */ typedef unsigned char char8_t; #endif __GLIBC_USE (ISOC2X) evaluates to true because gcc unconditionally defines _GNU_SOURCE. I believe otherwise, C++17 mode would only (or should only) imply __GLIBC_USE (ISOC11). Regardless, it seems that directives should be added to suppress the diagnostic. I tried prototyping such a fix, but it doesn't seem to work for me. I don't understand why. $ diff -U3 uchar.h.old uchar.h --- uchar.h.old 2022-07-20 12:37:55.544301692 -0400 +++ uchar.h     2022-07-20 12:43:21.124365563 -0400 @@ -34,8 +34,17 @@  /* Declare the C2x char8_t typedef in C2x modes, but only if the C++    __cpp_char8_t feature test macro is not defined.  */  #if __GLIBC_USE (ISOC2X) && !defined __cpp_char8_t +/* Suppress the C++20 compatability diagnostic regarding char8_t being a +   keyword.  */ +#if defined __GNUC__ && 4 < __GNUC__ + (6 <= __GNUC_MINOR__) +# pragma GCC diagnostic push +# pragma GCC diagnostic ignored "-Wc++20-compat" +#endif  /* Define the 8-bit character type.  */  typedef unsigned char char8_t; +#if defined __GNUC__ && 4 < __GNUC__ + (6 <= __GNUC_MINOR__) +# pragma GCC diagnostic pop +#endif  #endif  #ifndef __USE_ISOCXX11 Tom. On 7/19/22 5:08 PM, Joseph Myers wrote: > This change appears to introduce a failure of > wcsmbs/check-installed-headers-cxx with GCC mainline, because uchar.h now > produces: > > ../wcsmbs/uchar.h:38:23: error: identifier 'char8_t' is a keyword in C++20 [-Werror=c++20-compat] > 38 | typedef unsigned char char8_t; > > (recall we want our installed headers to avoid warnings *without* relying > on the default disabling of warnings in system headers). > > Unfortunately, GCC for C++ doesn't disable -Wc++20-compat inside > __extension__ (unlike what the C front end does), so simply adding > __extension__ to that declaration wouldn't help, but we could use > diagnostic disabling pragmas (as already done in some installed headers). >