[PATCH] D34158: For standards compatibility, preinclude <stdc-predef.h> if the file is available

[Fedor Sergeev via cfe-commits]

On Fri, Jul 28, 2017 at 02:07:29PM +0000, Blower, Melanie wrote:
>  
> 
> fedor.sergeev added a comment.
> 
> Hmm... I tried this patch and now the following worries me:
> 
> - it passes -finclude-if-exists stdc-predef.h on all platforms (say, including my Solaris platform that has no system stdc-predef.h)
> - it searches all the paths, not just "system include" ones
> 
> That essentially disallows user to have stdc-predef.h include in my own project, since there is a chance that this user header will be accidentally included by this hidden machinery.
> 
> >> Yes, I recognize this problem. However, I don't know an acceptable way to solve it. Does anyone have a recommendation? I had tried putting angle brackets around the file name string to imply a system-only search but that didn't work:  I guess the >angle brackets are taken to be part of the file name.  I believe it's intentional that has_include doesn't recognize the angle, I see test cases that have __has_include( "<...") Quoting from the patch:
> // For standards compliance, clang will preinclude <stdc-predef.h>
>     // -ffreestanding suppresses this behavior.
>     CmdArgs.push_back("-finclude-if-exists");
>     CmdArgs.push_back("<stdc-predef.h>"); // This doesn't work to restrict the search to system includes
>   } 
> 
> >I could change the argument scanner for __has_include to recognize the angle brackets -- would that be acceptable?  Alternatively, I could change the flag to be "finclude-if-exists" into "fsystem-include-if-exists". Then I could create a new preprocessing keyword(is that the right term?) __has_system_include and use that instead of __has_include.  
> 
> >I tried this test case with -c -E:
> >cat test1.c
> >#if __has_include( "stdio.h" )
> >#error it has stdio without angle  // This is printed
> >#else
> >#error it does not have stdio without angle
> >#endif
> 
> >#if __has_include( "<stdio.h>" )

According to:
  https://clang.llvm.org/docs/LanguageExtensions.html

a proper syntax here is without "s:

  #if __has_include(<stdio.h>)

regards,
  Fedor.

> >#error it has stdio with angle
> >#else
> >#error it does not have stdio with angle // This is printed
> >#endif
> 
>   ] cat stdc-predef.h
>   #error I was not expecting to see that
>   ] bin/clang hello-world.c
>   In file included from <built-in>:2:
>   ./stdc-predef.h:1:2: error: I was not expecting to see this!
>   #error I was not expecting to see this!
>    ^
>   1 error generated.
>   ]
> 
> 
> Repository:
>   rL LLVM
> 
> https://reviews.llvm.org/D34158
> 
> 
>