[CMake] Fortran project compiling with -isystem causing error

[Hugh Sorby]

Thanks Brad,

I looked at the documentation for gfortran and it says (before asking 
about my problem, I also read the CMake documentation but failed to 
comprehend it properly)

|-isystem|dir
    Searchdirfor header files, after all directories specified by-Ibut
    before the standard system directories. Mark it as a system
    directory, so that it gets the same special treatment as is applied
    to the standard system directories. Ifdirbegins with|=|, then
    the|=|will be replaced by the sysroot prefix; see--sysrootand-isysroot.

and

|-I|dir
    These affect interpretation of the|INCLUDE|directive (as well as of
    the|#include|directive of thecpppreprocessor).

    Also note that the general behavior of-Iand|INCLUDE|is pretty much
    the same as of-Iwith|#include|in thecpppreprocessor, with regard to
    looking forheader.gccfiles and other such things.

    This path is also used to search for.modfiles when previously
    compiled modules are required by a|USE|statement.

    SeeOptions for Directory Search
    <https://gcc.gnu.org/onlinedocs/gcc-4.4.4/gcc/Directory-Options.html#Directory-Options>,
    for information on the-Ioption.

I guess their documentation should be more explicit and say that 
-isystem dirs are not searched for .mod files.  The documentation as it 
stands implies to me that -isystem is the same as -I but for ordering.

Again thanks,
Hugh.

On 03/27/15 02:35, Brad King wrote:
> On 03/25/2015 08:26 PM, Hugh Sorby wrote:
>> |-- ex
>> |   |-- CMakeLists.txt
>> |   `-- use_mod.f90
>> |-- ex-build
>> |-- install
>> |-- modsrc
>> |   |-- CMakeLists.txt
>> |   `-- a.f90
>> `-- modsrc-build
> Thanks for the detailed example.  It was trivial to reproduce the
> issue with that!
>
> Since this commit:
>
>   Always consider includes from IMPORTED targets to be SYSTEM.
>   http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=a63fcbcb
>
> which was first included in CMake 3.0, include directories taken
> from imported targets are treated as SYSTEM automatically.  You
> can avoid it with a target property on the imported target:
>
>   http://www.cmake.org/cmake/help/v3.2/prop_tgt/NO_SYSTEM_FROM_IMPORTED.html
>
> Doing that will workaround the problem.  I think the real issue
> is that we cannot reliably use -isystem with gfortran at all
> because it won't look in such paths for module files.  I've
> fixed that here:
>
>   GNU: Do not use -isystem with gfortran
>   http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=a8e7a104
>
> Thanks,
> -Brad
>

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