From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp110.iad3a.emailsrvr.com (smtp110.iad3a.emailsrvr.com [173.203.187.110]) by sourceware.org (Postfix) with ESMTPS id 1148C3835839 for ; Fri, 22 Jul 2022 05:24:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 1148C3835839 X-Auth-ID: tom@honermann.net Received: by smtp6.relay.iad3a.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 46A2D3A65; Fri, 22 Jul 2022 01:24:15 -0400 (EDT) Message-ID: Date: Fri, 22 Jul 2022 01:24:14 -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> From: Tom Honermann In-Reply-To: <68dad418-f607-e0af-1983-df01ed1e422f@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Classification-ID: fde4b828-1bec-4850-9451-75792772b21c-1-1 X-Spam-Status: No, score=-2.1 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, RCVD_IN_MSPIKE_H2, 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 05:24:18 -0000 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? >> 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). 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). > >>>> $ 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. Yes, thank you. I also determined that the -Wc++20-compat option was added to gcc 10 and is only recognized in C++ modes, so the diagnostic suppression guards will be __GNUC_PREREQ (10, 0) && defined __cplusplus. I'll follow up with a patch soon. Tom. > >>>> +# 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). >>>>>