[Bug c/65377] New: [5.0 Regression] cpp attribute check ala clang fails to compile

[Bug c/65377] New: [5.0 Regression] cpp attribute check ala clang fails to compile

[npl at chello dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

            Bug ID: 65377
           Summary: [5.0 Regression] cpp attribute check ala clang fails
                    to compile
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: npl at chello dot at

The following code fails to compile with gcc-5-20150301, gcc 4.8.4 and 4.9.2
are fine.
The command used is simply "gcc test.c"

--------------------
#ifndef __has_cpp_attribute         // Optional of course.
#  define __has_cpp_attribute(x) 0  // Compatibility with non-clang compilers.
#endif

#if __has_cpp_attribute(clang::fallthrough) || (defined(__clang__) &&
__clang_major__ >= 4 || (__clang_major__ == 3 &&__clang_minor__ >= 3))
#  define FALLTHROUGH [[clang::fallthrough]];
#else
#  define FALLTHROUGH
#endif

int main()
{
}
--------------------


Error Message is:
test.c:5:30: error: missing ')' after "__has_attribute"
 #if __has_cpp_attribute(clang::fallthrough) || (defined(__clang__) &&
__clang_major__ >= 4 || (__clang_major__ == 3 &&__clang_minor__ >= 3))
                              ^
test.c:5:31: error:  ':' without preceding '?'
 #if __has_cpp_attribute(clang::fallthrough) || (defined(__clang__) &&
__clang_major__ >= 4 || (__clang_major__ == 3 &&__clang_minor__ >= 3))
                               ^

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Why should it?  We don't define __clang_major__.

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |trippels at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #2 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
If you want to compile C++ use g++.

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[npl at chello dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

npl at chello dot at changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |---

--- Comment #3 from npl at chello dot at ---
1) It simply shouldnt fail.
2) this is a generic header for C and C++.

__has_cpp_attribute(clang::fallthrough) should resolve to 0 and not fail. This
is a bug in gcc, unless you can explain why it shouldnt resolve to 0.

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
even "clang test.c" fails. Either rename it to test.cpp or use g++.

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Use the proper check if you are want check if you are compiling c++ code first.

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[npl at chello dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

--- Comment #6 from npl at chello dot at ---
(In reply to npl from comment #3)
> 1) It simply shouldnt fail.
> 2) this is a generic header for C and C++.
> 
> __has_cpp_attribute(clang::fallthrough) should resolve to 0 and not fail.
> This is a bug in gcc, unless you can explain why it shouldnt resolve to 0.

I think gcc should simply ignore the __has_cpp_attribute macro, unless it does
compile C++ code?
if I use other names than __has_cpp_attribute it compiles. I will put some C++
guards around this code, but I still think this is a bug?

(And I am compiling with Clang 3.4, but this doesnt support the feature check)

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

--- Comment #7 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
Unfortunately https://gcc.gnu.org/ml/gcc-patches/2015-01/msg02357.html hasn't
been checked in yet.

[Bug c/65377] [5.0 Regression] cpp attribute check ala clang fails to compile

[npl at chello dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65377

--- Comment #8 from npl at chello dot at ---
This (and the Iso recommendation) doesnt answer the question whether the
__has_cpp_attribute macro should be defined for C sources either (it seems
illogical to me).
Guess its undefined and not a bug, I wont bother you anymore =)