From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp64.ord1c.emailsrvr.com (smtp64.ord1c.emailsrvr.com [108.166.43.64]) by sourceware.org (Postfix) with ESMTPS id 0B26B3835839 for ; Thu, 21 Jul 2022 20:51:09 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 0B26B3835839 X-Auth-ID: tom@honermann.net Received: by smtp9.relay.ord1c.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 24BB1201B6; Thu, 21 Jul 2022 16:51:07 -0400 (EDT) Message-ID: <9940d0fb-0907-7ab2-2dc0-29236fc286a3@honermann.net> Date: Thu, 21 Jul 2022 16:51:04 -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: Adhemerval Zanella Netto , Joseph Myers Cc: libc-alpha@sourceware.org References: <20220630125215.6052-1-tom@honermann.net> <20220630125215.6052-3-tom@honermann.net> <6cf42820-86cb-f3ee-e4cf-3310de2e0bd1@honermann.net> From: Tom Honermann In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Classification-ID: 02be4a3f-5562-4438-aa36-68210664d711-1-1 X-Spam-Status: No, score=-2.8 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: Thu, 21 Jul 2022 20:51:11 -0000 On 7/21/22 3:22 PM, Adhemerval Zanella Netto wrote: > > On 20/07/22 13:47, Tom Honermann wrote: >> 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. > I have tried as well and I can't get to work either. It would expect to work > as we have done bits/stdlib-bsearch.h, could it be a gcc issue? Yes, this appears to be a gcc issue. I spent some time looking at gcc source code, but didn't find anything obvious. I verified the same technique does work to suppress the similar warning issued for use of, e.g., constexpr, as an identifier when -Wc++11-compat is enabled. I found tests that exercise #pragma GCC diagnostic ignored "-Wc++-compat", but none for -Wc++20-compat (or -Wc++11-compat). Tom. > >> $ 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). >>>