Explicitly specify ADIOS2 components in openPMDConfig.cmake (#1693)

* Explicitly specify ADIOS2 components in openPMDConfig.cmake

When including openPMD in downstream CMake and that CMake script
contains Fortran, ADIOS2 will automatically detect that. But since we
do not reexport the ADIOS2 headers, we only need the components that
openPMD explicitly uses: CXX and MPI.

* Same in CMakeLists.txt

CMakeLists.txt

@@ -360,20 +360,24 @@ if(openPMD_HDF5_STATUS)
 endif()
 
 # external library: ADIOS2 (optional)
+set(openPMD_REQUIRED_ADIOS2_COMPONENTS CXX)
+if(openPMD_HAVE_MPI)
+    list(APPEND openPMD_REQUIRED_ADIOS2_COMPONENTS MPI)
+endif()
 if(openPMD_USE_ADIOS2 STREQUAL AUTO)
-    find_package(ADIOS2 2.7.0 CONFIG)
+    find_package(ADIOS2 2.7.0 CONFIG COMPONENTS ${openPMD_REQUIRED_ADIOS2_COMPONENTS})
     if(ADIOS2_FOUND)
         set(openPMD_HAVE_ADIOS2 TRUE)
     else()
         set(openPMD_HAVE_ADIOS2 FALSE)
     endif()
 elseif(openPMD_USE_ADIOS2)
-    find_package(ADIOS2 2.7.0 REQUIRED CONFIG)
+    find_package(ADIOS2 2.7.0 REQUIRED CONFIG COMPONENTS ${openPMD_REQUIRED_ADIOS2_COMPONENTS})
     set(openPMD_HAVE_ADIOS2 TRUE)
 else()
     set(openPMD_HAVE_ADIOS2 FALSE)
 endif()
-# TODO: Check if ADIOS2 is parallel when openPMD_HAVE_MPI is ON
+unset(openPMD_REQUIRED_ADIOS2_COMPONENTS)
 
 # external library: pybind11 (optional)
 include(${openPMD_SOURCE_DIR}/cmake/dependencies/pybind11.cmake)

openPMDConfig.cmake.in

@@ -31,7 +31,12 @@ set(openPMD_HDF5_FOUND ${openPMD_HAVE_HDF5})
 
 set(openPMD_HAVE_ADIOS2 @openPMD_HAVE_ADIOS2@)
 if(openPMD_HAVE_ADIOS2)
-    find_dependency(ADIOS2)
+    set(openPMD_REQUIRED_ADIOS2_COMPONENTS CXX)
+    if(openPMD_HAVE_MPI)
+        LIST(APPEND openPMD_REQUIRED_ADIOS2_COMPONENTS MPI)
+    endif()
+    find_dependency(ADIOS2 COMPONENTS ${openPMD_REQUIRED_ADIOS2_COMPONENTS})
+    unset(openPMD_REQUIRED_ADIOS2_COMPONENTS)
 endif()
 set(openPMD_ADIOS2_FOUND ${openPMD_HAVE_ADIOS2})