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<p class="MsoNormal">Hi Marshall and others.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">After this discussion and some internal discussions I agree with the idea that files without extension are treated as C++ header files and non-header files should either move out of the C++ code base or have a proper extension. The VERSION
case is just the most visible case of it. The introduction of new headers that break existing projects can be handled with the use of -iquote or by using project specific names if people care about future proofing their projects. Makes me wonder if clang should
make -I to mean -iquote and have an -iangle option for the language headers instead. Anyway, I’m happy to leave it at this.<o:p></o:p></p>
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<p class="MsoNormal">Thanks for everybody’s time and thoughts on this.<o:p></o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Christof<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Marshall Clow <mclow.lists@gmail.com><br>
<b>Date: </b>Monday, 22 October 2018 at 15:41<br>
<b>To: </b>Christof Douma <Christof.Douma@arm.com><br>
<b>Cc: </b>"cfe-commits@lists.llvm.org" <cfe-commits@lists.llvm.org>, nd <nd@arm.com>, Arnaud De Grandmaison <Arnaud.DeGrandmaison@arm.com>, Jonathan Wakely <cxx@kayari.org><br>
<b>Subject: </b>Re: [libcxx] r342073 - Implement the infrastructure for feature-test macros. Very few actual feature test macros, though. Reviewed as: https://reviews.llvm.org/D51955<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On Tue, Oct 2, 2018 at 10:33 AM Christof Douma <<a href="mailto:Christof.Douma@arm.com">Christof.Douma@arm.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Hi Marshall.<br>
<br>
I think that this patch breaks backwards compatibility. Assumes that the header file "version" is used by C++ projects that use a C++ standard that did not specify a 'version' header. Many toolchains will put search paths specified with -I in front of the
system search path. The result is that the application header file is included whenever a standard header file is included. That is unexpected and can break builds.<br>
<br>
Do you agree this is an issue or do you consider this an issue with the way toolchains handle include search paths?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Christof -<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">I've been thinking about this the last few days.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">We can ameliorate this in libc++, (See Richard's suggestion on __version) but anything we do will be a short-term solution.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">The first time someone includes another header file that #include <version>, they're back to square one.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">That header is supposed to be "the place to go" for information about your standard library, and people are going to use it.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">For example, I expect that Boost.Config will start using it soon (if it doesn't already)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">A better solution (and not just because it would require other people to do the work) would be to have the build systems either:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">* Stop using VERSION as a file name - use something like VERSION.STAMP instead.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">* Use '-iquote' instead of '-I' to manage the list of include directories.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">I agree that it's annoying for people's builds to be broken when they upgrade their development tools,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">and especially when they didn't do anything "wrong".<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">-- Marshall<o:p></o:p></p>
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