[Plplot-devel] CMake fails to detect NaN for Fortran

[Rafael L. <ra...@la...>]

Dear PLplot developers,

When building the plplot package for Debian, using the latest version 
of gfortran:

     $ gfortran --version | head -n1
     GNU Fortran (Debian 12.2.0-9) 12.2.0

The CMake configuration fails to detect the NaN capability:

     -- Check if isnan function is available in fortran
     -- Check for isnan in fortran - not found

I see the following in CMakeFiles/CMakeError.log:

     Determining if fortran has isnan function failed with the following output:
     Change Dir: [path]/plplot/obj-x86_64-linux-gnu/CMakeFiles/CMakeTmp

     Run Build Command(s):/usr/bin/gmake -f Makefile cmTC_58c30/fast && gmake[2]: Entering directory '[path]/plplot/obj-x86_64-linux-gnu/CMakeFiles/CMakeTmp'
     /usr/bin/gmake  -f CMakeFiles/cmTC_58c30.dir/build.make CMakeFiles/cmTC_58c30.dir/build
     gmake[3]: Entering directory '[path]/plplot/obj-x86_64-linux-gnu/CMakeFiles/CMakeTmp'
     Building Fortran object CMakeFiles/cmTC_58c30.dir/TestFortranIsnan.f.o
     /usr/bin/gfortran   -g -O2 -ffile-prefix-map=[path]/plplot=. -fstack-protector-strong -fvisibility=hidden  -c [path]/plplot/cmake/modules/TestFortran
     Isnan.f -o CMakeFiles/cmTC_58c30.dir/TestFortranIsnan.f.o
     [path]/plplot/cmake/modules/TestFortranIsnan.f:5:19:

         5 |       if (isnan(0.0/0.0)) then
           |                   1
     Error: Division by zero at (1)
     [path]/plplot/cmake/modules/TestFortranIsnan.f:7:9:

         7 |       endif
           |         1
     Error: Expecting END PROGRAM statement at (1)
     gmake[3]: *** [CMakeFiles/cmTC_58c30.dir/build.make:78: CMakeFiles/cmTC_58c30.dir/TestFortranIsnan.f.o] Error 1

The patch attached to this message fixes the problem. I think that the 
problems arises because the gfortran compiler is trying to do the 
computation "0.0/0.0" at compile-time.

Best,

Rafael Laboissière