[CMake] CMAKE_<languageName>_COMPILER_WORKS no longer cached?!

[Marcel Loose]

Hi all,

I noticed that, as of CMake 2.8.10, the variable 
CMAKE_<languageName>_COMPILER_WORKS is no longer cached. This breaks 
some of my code.

I have wrapped find_package() into a my own project-specific 
CMake-function <myproject>_find_package(). In one of my Find*.cmake 
files I do a enable_language(Fortran) and check the value of 
CMAKE_Fortran_COMPILER_WORKS. The thing is, this works when this Find* 
macro is called for the first time, but not for subsequent calls; and I 
think it is caused by the fact that CMAKE_Fortran_COMPILER_WORKS is no 
longer cached.

Stripping away the irrelevant parts of my Find module, here's what remains:

# Enable the Fortran compiler, if that has not been done yet.
get_property(_enabled_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
if(NOT _enabled_languages MATCHES Fortran)
   # Work-around for CMake issue #9220
   if(CMAKE_Fortran_COMPILER MATCHES "^$")
     set(CMAKE_Fortran_COMPILER CMAKE_Fortran_COMPILER-NOTFOUND)
   endif(CMAKE_Fortran_COMPILER MATCHES "^$")
   enable_language(Fortran)
endif(NOT _enabled_languages MATCHES Fortran)

# Check if we have a working Fortran compiler
if(CMAKE_Fortran_COMPILER_WORKS)
   # Do some fancy stuff.
else(CMAKE_Fortran_COMPILER_WORKS)
   message(SEND_ERROR "A working Fortran compiler is required!")
endif(CMAKE_Fortran_COMPILER_WORKS)

When this Find module is called for the first time by 
<myproject>_find_package(), the "Do some fancy stuff" is done. On 
subsequent calls, however, the error is triggered, because 
CMAKE_Fortran_COMPILER_WORKS is empty.

What's the correct way of handling this, without breaking backward 
compatibility?

Best regards,
Marcel Loose.

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