From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp113.iad3b.emailsrvr.com (smtp113.iad3b.emailsrvr.com [146.20.161.113]) by sourceware.org (Postfix) with ESMTPS id 3C56438582A8 for ; Fri, 22 Jul 2022 17:00:17 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 3C56438582A8 X-Auth-ID: tom@honermann.net Received: by smtp23.relay.iad3b.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 9E159A014C; Fri, 22 Jul 2022 13:00:16 -0400 (EDT) Message-ID: <98ac49a5-519c-dd5f-ea0b-e6ad5efdfb59@honermann.net> Date: Fri, 22 Jul 2022 13:00:16 -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> <9940d0fb-0907-7ab2-2dc0-29236fc286a3@honermann.net> <68dad418-f607-e0af-1983-df01ed1e422f@linaro.org> <83387a91-fe6b-ba45-3906-448f2d9c98cd@linaro.org> <9166be9c-bf3e-46f9-d867-e007adc27eb2@linaro.org> From: Tom Honermann In-Reply-To: <9166be9c-bf3e-46f9-d867-e007adc27eb2@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Classification-ID: 7a29daaa-bb5c-4dde-b4c9-5bb09d74d0cc-1-1 X-Spam-Status: No, score=-2.3 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: Fri, 22 Jul 2022 17:00:18 -0000 On 7/22/22 10:15 AM, Adhemerval Zanella Netto wrote: > > On 22/07/22 08:21, Adhemerval Zanella Netto wrote: >> >> On 22/07/22 02:24, Tom Honermann wrote: >>> On 7/21/22 4:56 PM, Adhemerval Zanella Netto wrote: >>>> 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? >>>>> prereqYes, 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). >>> I agree. I debugged gcc tonight and discovered what the problem was. I'll submit a patch to gcc. >>>> We also need to avoid >>>> declare the typedef for __cplusplus >= 202002L. >>> The typedef is already avoided if the __cpp_char8_t feature test macro is defined (builtin char8_t support can be enabled in previous C++ standard modes via the -fchar8_t option). >> If the compiler preprocessor defined for -std=c++20? I had the impression it is >> enabled iff -fchar8_t is set. > I realized now I did not write proper english, I meant to ask if gcc always define > __cpp_char8_t for -std=c++20 and higher since I had the impression that the > define is only active iff -fchar8_t is actively used. English is hard :) For gcc, clang, and MSVC, -std=c++20 (/std:c++20 for MSVC) implies -fchar8_t (/Zc:char8_t), but that feature can be disabled with -fno-char8_t (/Zc:char8_t-). For example: $ gcc -E -dM -x c++ -std=c++17 /dev/null | grep __cpp_char8_t $ gcc -E -dM -x c++ -std=c++17 -fchar8_t /dev/null | grep __cpp_char8_t #define __cpp_char8_t 201811L $ gcc -E -dM -x c++ -std=c++20 /dev/null | grep __cpp_char8_t #define __cpp_char8_t 201811L $ gcc -E -dM -x c++ -std=c++20 -fno-char8_t /dev/null | grep __cpp_char8_t Tom.