[CMake] Issue with check_include_file() and GL/glxproto.h

[GOUJON Alexandre]

On 11/11/2011 04:13 AM, Michael Hertling wrote:
> On 11/10/2011 11:22 PM, Eric Noulard wrote:
>> If this is the case then it is a "GL/glxproto.h" design mistake
>> not CMake mistake.
> Absolutely, try to compile the following program by hand; it's
> the same the CHECK_INCLUDE_FILE() macro tries to compile, too:
>
> #include<GL/glxproto.h>
> int main(void){return 0;}
>
> It will fail with the same error message, i.e. the GL/glxproto.h header
> is not self-sufficient; if intentionally or accidentally, I don't know.
> It's this failure that makes CHECK_INCLUDE_FILE() report the header as
> non-existent, or better as "not compilable".
I just sent them an e-mail so that they will be aware of the issue.

>> This is true but the documentation tells you more about the macro
>> cmake --help-module CheckIncludeFile
>>
>> says
>> "an optional third argument is the CFlags to add to the compile line or
>>         you can use CMAKE_REQUIRED_FLAGS"
>>
>> which clearly states that it does a compilation.
> Indeed, CHECK_INCLUDE_FILE() means: Check if a header is *functional*.
Ok, will use find_file instead.
>> The thing you want is probably
>>
>> if(DEFINED VARIABLE)
>>     message(FATAL_ERROR "VARIABLE already defined :<${VARIABLE}>  aborting")
>> endif()
Yeah, thanks.
>> I think it's not the responsability of check_include_file to do such job
>> but you can do that in your CMakeLists.txt
> With FIND_FILE/PATH() looking for a header, the user must have the
> possibility to make them no-ops by presetting the result variable,
> so these functions must not overwrite a valid path. However, with
> CHECK_INCLUDE_FILE(), the user can't "define" a header as working;
> thus, there is no need to protect an already defined variable from
> being overwritten, IMO. Moreover, the user must have the chance to
> reuse the same variable for this purpose again without having the
> configuration terminate. OTOH, one usually uses an individually
> named variable for each header, e.g. HAVE_GL_GLXPROTO_H, as you
> do, which is most certainly not reused for anything at all.
Ok but as I didn't understand why check_include_file was failing, I 
tried many things like simple then double quoting GL/glxproto.h and also 
tried a different variable name. I took HAVE_UNISTDE_H because I knew 
HAVE_UNISTD_H was working. With HAVE_UNISTDE_H, check_include_file 
seemed to work (it wasn't true, this variable name was simply defined 
before elsewhere) so in the end, I believed some variable names were 
allowed and others not. So to avoid the same mistake, I thought a 
message (at least a STATUS one) wouldn't hurt.
>>> IF("${VARIABLE}" MATCHES "^${VARIABLE}$") fails : is it intended ?
>> I do not understand
>> In which case does it fail?
Actually, every time.
Here is the beginning of my modified CheckIncludeFile.cmake :

MACRO(CHECK_INCLUDE_FILE INCLUDE VARIABLE)
message(STATUS "${VARIABLE}")
   IF("${VARIABLE}" MATCHES "^${VARIABLE}$")
message(STATUS "${VARIABLE} matches ^${VARIABLE}$")

and I only have the following output
-- HAVE_SYS_TIME_H
-- HAVE_SYS_TYPES_H
-- HAVE_SYS_RESOURCE_H
-- HAVE_SYS_STAT_H
-- HAVE_UNISTD_H
-- HAVE_FCNTL_H
-- HAVE_GL_GLXPROTO_H
CMake Error at CMakeLists.txt:117 (message):
[..]

So the first IF is failing, skipping the whole macro.
If I add a # before this IF (and the corresponding ENDIF), 
check_include_file does its jobs and even finds the other headers :
[...]
-- HAVE_FCNTL_H
-- HAVE_FCNTL_H matches ^HAVE_FCNTL_H$
-- Looking for fcntl.h
-- Looking for fcntl.h - found
-- HAVE_GL_GLXPROTO_H
-- HAVE_GL_GLXPROTO_H matches ^HAVE_GL_GLXPROTO_H$
-- Looking for GL/glxproto.h
-- Looking for GL/glxproto.h - not found

Any idea ?