[cmake-developers] C++11 and target_compiler_feature proposal

[Stephen Kelly]

Stephen Kelly wrote:

> We'll initially defer the concept of generating a header file with
> defines/MyStaticAssert etc.

I've looked into this a bit. The previous discussion on this ended here:

 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/6726/focus=7814

I'm still not sure that generating a header specific to the compiler (ID and 
version) is a good idea. 

That means that if I build a binary package of my library using GCC, and I 
list cxx_final as an optional feature, you can't use clang with my binary 
package.

Qt makes binary packages for x86 and x86_64 available, not both for each 
compiler:

 http://master.qt-project.org/snapshots/qt/5.2/5.2.0-beta1/2013-10-21_107/

The generate_export_header feature is also different, in that the header it 
generates is compatible between different compilers on linux (because clang 
chose to be compatible I suppose).

So, I think maybe it would make sense to list features separately, and if 
someone does this:

 write_compiler_detection_header(
   FILE ${CMAKE_CURRENT_BINARY_DIR}/grantlee_compiler_detection.h
   PREFIX Grantlee_
   FEATURES cxx_final cxx_override
 )

the generated header would look something like this:

 #ifndef GRANTLEE_COMPILER_DETECTION_H
 #define GRANTLEE_COMPILER_DETECTION_H

 #if defined(__GNU__) && !defined(__clang__) 
 #  if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCH__) >= 407
 #    define Grantlee_FINAL final
 #    define Grantlee_OVERRIDE override
 #  else 
 #    define Grantlee_FINAL
 #    define Grantlee_OVERRIDE 
 #  endif
 #elif defined(__clang__)
 #  if __has_feature(cxx_explicit_conversions)
 #    define Grantlee_FINAL final
 #    define Grantlee_OVERRIDE override
 #  else 
 #    define Grantlee_FINAL
 #    define Grantlee_OVERRIDE 
 #  endif
 #elif defined(_MSC_VER) 
 // TODO: This could also be intel or other pretenders. Handle that too.
 #  if _MSC_VER >= 1700
 #    define Grantlee_FINAL final
 #    define Grantlee_OVERRIDE override
 #  else 
 #    define Grantlee_FINAL
 #    define Grantlee_OVERRIDE 
 #  endif
 // TODO: Other compilers
 #endif

 #endif


Any further comments?

Thanks,

Steve.