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

[Blower, Melanie via cfe-commits]

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>" )
>#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