Fortran: disable auto-detection of fortran bindings

Auto-detection of language available doesn't correctly work in CMake so
just explicitly default to OFF here and error out if set to AUTO.

CMakeLists.txt

@@ -90,7 +90,7 @@ adios_option(ZeroMQ    "Enable support for ZeroMQ" AUTO)
 adios_option(HDF5      "Enable support for the HDF5 engine" AUTO)
 adios_option(ADIOS1    "Enable support for the ADIOS 1.x engine" AUTO)
 adios_option(Python    "Enable support for Python bindings" AUTO)
-adios_option(Fortran   "Enable support for Fortran bindings" AUTO)
+adios_option(Fortran   "Enable support for Fortran bindings" OFF)
 adios_option(SysVShMem "Enable support for SysV Shared Memory IPC on *NIX" AUTO)
 include(${ADIOS2_SOURCE_DIR}/cmake/DetectOptions.cmake)
 

cmake/DetectOptions.cmake

@@ -33,25 +33,32 @@ if(ZFP_FOUND)
   set(ADIOS2_HAVE_ZFP TRUE)
 endif()
 
+set(mpi_find_components C)
+
+# Fortran
+if(ADIOS2_USE_Fortran STREQUAL AUTO)
+  # Currently auto-detection for language support does not work in CMake.  See
+  # documentation for the "enable_language" command
+  message(WARN "Auto-detection of Fortran is not currently supported; Disabling")
+  #enable_language(Fortran OPTIONAL)
+elseif(ADIOS2_USE_Fortran)
+  enable_language(Fortran)
+endif()
+if(CMAKE_Fortran_COMPILER_LOADED)
+  set(ADIOS2_HAVE_Fortran TRUE)
+  list(APPEND mpi_find_components Fortran)
+endif()
+
 # MPI
 if(ADIOS2_USE_MPI STREQUAL AUTO)
-  find_package(MPI)
+  find_package(MPI COMPONENTS ${mpi_find_components})
 elseif(ADIOS2_USE_MPI)
-  find_package(MPI REQUIRED)
+  find_package(MPI COMPONENTS ${mpi_find_components} REQUIRED)
 endif()
 if(MPI_FOUND)
   set(ADIOS2_HAVE_MPI TRUE)
 endif()
 
-# Fortran
-if(ADIOS2_USE_Fortran)
-  set(ADIOS2_HAVE_Fortran TRUE)
-  enable_language(Fortran)
-  if(ADIOS2_HAVE_MPI)
-    find_package(MPI COMPONENTS Fortran REQUIRED)
-  endif()
-endif()
-
 # DataMan
 if(SHARED_LIBS_SUPPORTED AND NOT MSVC)
   set(ADIOS2_HAVE_DataMan TRUE)