[CMake] CMAKE_COMPILER_IS_GNUC vs. CMAKE_COMPILER_IS_GNUCC

[Todd Gamblin]

On Jul 5, 2010, at 1:23 AM, Michael Wild wrote:

> 
> On 5. Jul, 2010, at 7:46 , Todd Gamblin wrote:
> 
>> The documentation here:
>> 
>> 	http://*www.*cmake.org/cmake/help/cmake2.6docs.html#variable:CMAKE_COMPILER_IS_GNULANG
>> 
>> is in conflict with the documentation here:
>> 
>> 	http://*www.*cmake.org/Wiki/CMake_Useful_Variables
>> 
>> And this thread (though it's from 2008) seems to imply that the second link above is right, even though the first is more current:
>> 
>> 	http://*www.*mail-archive.com/cmake@cmake.org/msg16863.html
>> 
>> 
>> I'm using CMake 2.8.2, and I'm noticing that CMAKE_COMPILER_IS_GNUC is empty, which conflicts with the latest documentation on the wiki.  This makes it hard to do things like this:
>> 
>>> 	for (lang C CXX Fortran)
>>> 		if (CMAKE_COMPILER_IS_GNU${lang})
>>> 			...
>>> 		endif()
>>> 	endfor()
>> 
>> Looking through the CMake source, it doesn't look like CMAKE_COMPILER_IS_GNUFortran is used anywhere.  I tested it, and it looks like it's empty too.  Would it be possible to add CMAKE_COMPILER_IS_GNUC and CMAKE_COMPILER_IS_GNUFortran so that they actually work?  I think this would be more consistent than the current setup.
>> 
>> These issues are coming up in the platform files I'm making for BlueGeneP.  I think writing things like this would be easier if this were more consistent.
>> 
>> -Todd
> 
> The variables are called CMAKE_COMPILER_IS_GNUC, CMAKE_COMPILER_IS_GNUCXX and CMAKE_COMPILER_IS_GNUG77 (the latter is admittedly weird)

I don't think this is correct, at least not in the platform files in CMake 2.8.2.  If I look at the value of CMAKE_COMPILER_IS_GNUC, it's empty.  If I look at CMAKE_COMPILER_IS_GNUCC, it's getting set to what I'd expect.  Is CMAKE_COMPILER_IS_GNUC set somewhere else, after the platform file gets included?

G77 is weird, since as far as I can tell it's "Fortran" for all the other variables.  Like I said, that really precludes you from doing something like this, especially if you try to set something inside the loop:

	for (lang C CXX Fortran)
		if (CMAKE_COMPILER_IS_GNU${lang})
			set(CMAKE_SHARED_LIBRARY_CREATE_${lang}_FLAGS "-shared")
		endif()
	endfor()

Since now ${lang} needs to be something different in all those places.

> 
> Michael