r289018 - [Headers] Enable #include_next<float.h> on Darwin

[Bruno Cardoso Lopes via cfe-commits]

On Tue, Apr 25, 2017 at 6:29 AM, Aaron Ballman <aaron at aaronballman.com> wrote:
> On Wed, Dec 7, 2016 at 9:13 PM, Bruno Cardoso Lopes via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
>> Author: bruno
>> Date: Wed Dec  7 20:13:56 2016
>> New Revision: 289018
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=289018&view=rev
>> Log:
>> [Headers] Enable #include_next<float.h> on Darwin
>>
>> Allows darwin targets to provide additional definitions and
>> implementation specifc values for float.h
>>
>> rdar://problem/21961491
>>
>> Added:
>>     cfe/trunk/test/Headers/Inputs/usr/
>>     cfe/trunk/test/Headers/Inputs/usr/include/
>>     cfe/trunk/test/Headers/Inputs/usr/include/float.h
>>     cfe/trunk/test/Headers/float-darwin.c
>> Modified:
>>     cfe/trunk/lib/Headers/float.h
>
> This commit appears to have caused a regression:
> https://bugs.llvm.org//show_bug.cgi?id=31504
>
> I am running into this on a Snow Leopard system as well, where the
> Integration tests are now failing because float.h cannot be found by
> the system #include_next.

What's actually happening here is that Snow Leopard (or any < 10.7)
used to ship a /usr/include/float.h, which has by itself another
include_next (which is the one failing), see:

--
/* This file exists soley to keep Metrowerks' compilers happy.  The version
   used by GCC can be found in /usr/lib/gcc, although it's
   not very informative.  */

#ifndef _FLOAT_H_

#if defined(__GNUC__)
#include_next <float.h>
--

We don't have any reliable way to check for the SDK version at this
level, the current macros we have tell a history about deployment
target, but that won't always solve the issue here. Can you try this
workaround below and let me know if works?

--
#if (defined(__APPLE__) || (defined(__MINGW32__) || defined(_MSC_VER))) && \
   __STDC_HOSTED__ && __has_include_next(<float.h>)

#ifdef __APPLE__
#define _FLOAT_H_ // Avoid #include_next'ing float.h content on MacOSX < 10.7
#endif

#  include_next <float.h>
--

> I was thinking of modifying lib/Headers/float.h to use the SDK version as mentioned in the bug report, but I share the reporter's question: why was this change needed in the first place? I couldn't find a review for the commit, and don't have access to the rdar link.

We need it to have flexibility to implement additional stuff for
float.h on future SDKs. There was no good reason for not upstreaming
it. I never got to the point of dealing with this specific issue
though, thanks for pinging.

-- 
Bruno Cardoso Lopes
http://www.brunocardoso.cc