[cmake] Re-introducuce OGS_BUILD_PROCESS_XYZ.

- OGS_BUILD_PROCESSES_XYZ work as before.
- OGS_BUILD_PROCESSES is not a cache variable anymore but beside it
  works as before and also allows for multiple processes.
- OGS_BUILD_PROCESSES takes precedence before (overwrites) BUILD_PROCESSES_XYZ.

CMakeLists.txt

@@ -272,3 +272,5 @@ include(scripts/cmake/MarkVariablesAdvanced.cmake)
 unset(PRE_INSTALL_RUN CACHE)
 
 include(Features)
+
+printEnabledProcesses()

scripts/cmake/ProcessesSetup.cmake

@@ -28,19 +28,15 @@ set(_processes_list
     TwoPhaseFlowWithPrho
 )
 
-set(OGS_BUILD_PROCESSES ON
-    CACHE STRING "Semicolon-separated list of processes to build"
-)
-
-# Drop-down (cmake-gui), cycle-through list (ccmake) for easiere interactive
-# selection. For enabling multiple selected processes cmake usage via cli is
-# required!
-set_property(
-    CACHE OGS_BUILD_PROCESSES PROPERTY STRINGS ON OFF ${_processes_list}
-)
+foreach(process ${_processes_list})
+    option(OGS_BUILD_PROCESS_${process} "Build process ${process}" ON)
+    if(OGS_BUILD_PROCESS_${process})
+        list(APPEND _enabled_processes ${process})
+    endif()
+endforeach()
 
 if(NOT OGS_BUILD_CLI)
-    set(OGS_BUILD_PROCESSES OFF "" CACHE STRING "" FORCE)
+    set(OGS_BUILD_PROCESSES OFF)
     message(
         STATUS
             "ATTENTION: OGS_BUILD_CLI=OFF -> OGS_BUILD_PROCESSES is set to OFF too.\n"
@@ -49,33 +45,58 @@ if(NOT OGS_BUILD_CLI)
     )
 endif()
 
-if("${OGS_BUILD_PROCESSES}" STREQUAL "ON" OR "${OGS_BUILD_PROCESSES}" STREQUAL
-                                             "OFF"
-)
-    if(OGS_BUILD_PROCESSES)
-        message(STATUS "All processes enabled.")
-        set(_enabled_processes ${_processes_list})
+if(DEFINED CACHE{OGS_BUILD_PROCESSES})
+    if("${OGS_BUILD_PROCESSES}" STREQUAL "ON" OR "${OGS_BUILD_PROCESSES}"
+                                                 STREQUAL "OFF"
+    )
+        if(OGS_BUILD_PROCESSES)
+            set(_enabled_processes ${_processes_list})
+        else()
+            unset(_enabled_processes)
+        endif()
     else()
-        message(STATUS "All processes disabled.")
-        unset(_enabled_processes)
+        foreach(process ${OGS_BUILD_PROCESSES})
+            if(NOT "${process}" IN_LIST _processes_list)
+                message(
+                    FATAL_ERROR
+                        "${process} given in OGS_BUILD_PROCESSES is "
+                        "not a valid process name! Valid names are ${_processes_list}"
+                )
+            endif()
+        endforeach()
+        set(_enabled_processes ${OGS_BUILD_PROCESSES})
     endif()
-else()
-    foreach(process ${OGS_BUILD_PROCESSES})
-        if(NOT "${process}" IN_LIST _processes_list)
-            message(
-                FATAL_ERROR
-                    "${process} given in OGS_BUILD_PROCESSES is "
-                    "not a valid process name! Valid names are ${_processes_list}"
-            )
+    foreach(process ${_processes_list})
+        if(${process} IN_LIST _enabled_processes)
+            set(OGS_BUILD_PROCESS_${process} ON CACHE BOOL "" FORCE)
+        else()
+            set(OGS_BUILD_PROCESS_${process} OFF CACHE BOOL "" FORCE)
         endif()
     endforeach()
-    set(_enabled_processes ${OGS_BUILD_PROCESSES})
-    message(STATUS "Enabled processes: ${OGS_BUILD_PROCESSES}")
+    unset(OGS_BUILD_PROCESSES CACHE)
 endif()
 
-if("${OGS_BUILD_PROCESSES}" STREQUAL "ON" OR "RichardsComponentTransport"
-                                             IN_LIST OGS_BUILD_PROCESSES
-   OR "ComponentTransport" IN_LIST OGS_BUILD_PROCESSES
+if("RichardsComponentTransport" IN_LIST _enabled_processes
+   OR "ComponentTransport" IN_LIST _enabled_processes
 )
     set(_build_chemistry_lib ON)
 endif()
+
+# Print summary of enabled processes.
+function(printEnabledProcesses)
+    list(LENGTH _enabled_processes num_enabled_processes)
+    list(LENGTH _processes_list num_processes_list)
+    if(${num_enabled_processes} EQUAL 0)
+        message(STATUS "All processes have been disabled!\n")
+        return()
+    endif()
+    if(${num_processes_list} EQUAL ${num_enabled_processes})
+        message(STATUS "All processes have been enabled.\n")
+        return()
+    endif()
+    message(STATUS "The following processes have been enabled:\n")
+    foreach(process ${_enabled_processes})
+        message(" * ${process}")
+    endforeach()
+    message("")
+endfunction()