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([2804:431:c7cb:8ded:90a7:7be2:9a21:5f25]) by smtp.gmail.com with ESMTPSA id m29-20020a056870059d00b0010d7e268e1esm1481205oap.10.2022.07.21.13.56.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Jul 2022 13:56:45 -0700 (PDT) Message-ID: <68dad418-f607-e0af-1983-df01ed1e422f@linaro.org> Date: Thu, 21 Jul 2022 17:56:43 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.0.2 Subject: Re: [PATCH v4 2/3] stdlib: Implement mbrtoc8(), c8rtomb(), and the char8_t typedef. Content-Language: en-US To: Tom Honermann , 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> <9940d0fb-0907-7ab2-2dc0-29236fc286a3@honermann.net> From: Adhemerval Zanella Netto Organization: Linaro In-Reply-To: <9940d0fb-0907-7ab2-2dc0-29236fc286a3@honermann.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-4.3 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 20:56:48 -0000 On 21/07/22 17:51, Tom Honermann wrote: > 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. > In any case I think the fix below is the correct way (in fact I don't see another way so I am assuming a compiler issue here). We also need to avoid declare the typedef for __cplusplus >= 202002L. >> >>> $ 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__) Use __GNUC_PREREQ. >>> +# 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). >>>>