<div dir="ltr"><div dir="ltr">On Thu, Jan 24, 2019 at 12:06 PM <<a href="mailto:paul.robinson@sony.com">paul.robinson@sony.com</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Not to be super snarky, but is there some reason why Chrome project preferences must be encoded into Clang compiler features?</span></p></div></div></blockquote><div><br></div><div>It's more "encoded in build files instead of in source code". We pull in source code from ~100 third-party repos. We have custom build files for all of them, but don't control the code in there.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div lang="EN-US"><div class="gmail-m_-2291533962270354526WordSection1"><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">This is really a stylistic choice in how you want to manage your project.</span></p></div></div></blockquote><div><br></div><div>In general, clang is pretty flexible in how it can be used, so that it matches use cases of different projects. For example, you can enable warnings via flags or pragmas, or there's blanket -Werror vs -Werror=each_individual_flag, etc etc etc. There isn't really a need to offer more than one option, but different options are convenient for different projects.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div lang="EN-US"><div class="gmail-m_-2291533962270354526WordSection1"><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> There's no end to the potential who-wins argument, whether it should be '#pragma
dammit' or the '—dammit' command line option. We have one way in place, and you have other tactics available to enforce a different choice.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">--paulr<u></u><u></u></span></p>
<p class="MsoNormal"><a name="m_-2291533962270354526__MailEndCompose"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></a></p>
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<p class="MsoNormal"><b><span style="font-size:10pt;font-family:Tahoma,sans-serif">From:</span></b><span style="font-size:10pt;font-family:Tahoma,sans-serif"> cfe-dev [mailto:<a href="mailto:cfe-dev-bounces@lists.llvm.org" target="_blank">cfe-dev-bounces@lists.llvm.org</a>]
<b>On Behalf Of </b>James Y Knight via cfe-dev<br>
<b>Sent:</b> Thursday, January 24, 2019 12:00 PM<br>
<b>To:</b> Nico Weber<br>
<b>Cc:</b> cfe-dev<br>
<b>Subject:</b> Re: [cfe-dev] Does `#pragma GCC diagnostic warning` intentionally win over -Werror?<u></u><u></u></span></p>
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<p class="MsoNormal">Perhaps a lint rule triggering on "#pragma GCC diagnostic warning", saying "We don't allow warnings, please use `#pragma GCC diagnostic error` (or ignored)" would solve the problem sufficiently.<u></u><u></u></p>
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<p class="MsoNormal">Separately, I note that "#pragma GCC diagnostic error" allows errors to bypass -Wfatal-errors. That certainly seems to serve no useful purpose and could be removed.<u></u><u></u></p>
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<p class="MsoNormal">On Thu, Jan 24, 2019 at 11:20 AM Nico Weber <<a href="mailto:thakis@chromium.org" target="_blank">thakis@chromium.org</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">On Thu, Jan 24, 2019 at 11:12 AM James Y Knight <<a href="mailto:jyknight@google.com" target="_blank">jyknight@google.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">I don't think we should have such a flag. The explicit intent of '#pragma gcc diagnostic warning' is to allow downgrading an error to a warning, while still allowing it to be emitted.<u></u><u></u></p>
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<p class="MsoNormal">Perhaps a new value for pragma diagnostic which emits an upgradeable warning would be reasonable.<u></u><u></u></p>
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<p class="MsoNormal">The use case here is that we don't allow non-error diagnostics in chrome. Some subproject used `#pragma GCC diagnostic warning` because they wanted to configure warning flags in cc files instead of in build files for some reason. They didn't
expect this to trigger a warning instead of an error. A new pragma would meet that use case, but I don't want source code to be able to opt out of -Werror. In my experience, once it's known that such an option exist, someone will use it. So we do need some
kind of "_all_ warnings are errors" toggle.<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">On Thu, Jan 24, 2019 at 9:56 AM Nico Weber via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Re "intentional?", it matches gcc which explicitly documents on <a href="https://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html" target="_blank">https://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html</a> that the pragma wins over
-Werror.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">Does anyone know if there's a flag that says "I want all warnings to be errors, not just most of them"?<u></u><u></u></p>
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<p class="MsoNormal">If there isn't one yet, what would be a good UI for that?<u></u><u></u></p>
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<p class="MsoNormal">On Wed, Jan 23, 2019 at 11:11 PM Nico Weber <<a href="mailto:thakis@chromium.org" target="_blank">thakis@chromium.org</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Consider:<u></u><u></u></p>
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<p class="MsoNormal">$ cat test.cc<u></u><u></u></p>
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<p class="MsoNormal">#pragma GCC diagnostic warning "-Wsign-compare"<u></u><u></u></p>
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<p class="MsoNormal">bool f(int a, unsigned b) {<u></u><u></u></p>
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<p class="MsoNormal"> return a != b;<u></u><u></u></p>
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<p class="MsoNormal">}<u></u><u></u></p>
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<p class="MsoNormal">$ out/gn/bin/clang -c test.cc -Werror<u></u><u></u></p>
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<p class="MsoNormal">test.cc:4:12: warning: comparison of integers of different signs: 'int' and 'unsigned int' [-Wsign-compare]<u></u><u></u></p>
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<p class="MsoNormal"> return a != b;<u></u><u></u></p>
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<p class="MsoNormal"> ~ ^ ~<u></u><u></u></p>
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<p class="MsoNormal">1 warning generated.<u></u><u></u></p>
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<p class="MsoNormal">I found it surprising that this is emitted as a warning, not as an error. If this is intentional, is there some other way to say "I want my compiler warnings to always be errors"?<u></u><u></u></p>
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<p class="MsoNormal"><br>
Thanks,<u></u><u></u></p>
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<p class="MsoNormal">Nico<u></u><u></u></p>
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