[CMake] Use output name of MODULE target also for dictionary name

Use output name of `MODULE` target also for the dictionary name, if the
target is defined. This makes the dictionary and library file names more
consistent.

Closes #15792.

Author: guitargeek

cmake/modules/RootMacros.cmake

@@ -515,22 +515,23 @@ function(ROOT_GENERATE_DICTIONARY dictionary)
   endforeach()
 
   #---Build the names for library, pcm and rootmap file ----
-  set(library_target_name)
-  if(dictionary MATCHES "^G__")
+  if(TARGET ${ARG_MODULE})
+    get_target_property(library_target_name ${ARG_MODULE} OUTPUT_NAME)
+  elseif(dictionary MATCHES "^G__")
     string(REGEX REPLACE "^G__(.*)" "\\1"  library_target_name ${dictionary})
     if (ARG_MULTIDICT)
       string(REGEX REPLACE "(.*)32$" "\\1"  library_target_name ${library_target_name})
     endif (ARG_MULTIDICT)
   else()
     get_filename_component(library_target_name ${dictionary} NAME_WE)
   endif()
-  if (ARG_MODULE)
+  if (ARG_MODULE AND NOT TARGET ${ARG_MODULE})
     if (NOT ${ARG_MODULE} STREQUAL ${library_target_name})
 #      message(AUTHOR_WARNING "The MODULE argument ${ARG_MODULE} and the deduced library name "
 #        "${library_target_name} mismatch. Deduction stem: ${dictionary}.")
       set(library_target_name ${ARG_MODULE})
     endif()
-  endif(ARG_MODULE)
+  endif()
 
   #---Set the library output directory-----------------------
   ROOT_GET_LIBRARY_OUTPUT_DIR(library_output_dir)
@@ -558,7 +559,7 @@ function(ROOT_GENERATE_DICTIONARY dictionary)
         set(cpp_module_file ${library_output_dir}/${cpp_module}.pcm)
         # The module depends on its modulemap file.
         if (cpp_module_file AND CMAKE_PROJECT_NAME STREQUAL ROOT)
-		set (runtime_cxxmodule_dependencies copymodulemap "${CMAKE_BINARY_DIR}/include/ROOT.modulemap")
+          set (runtime_cxxmodule_dependencies copymodulemap "${CMAKE_BINARY_DIR}/include/ROOT.modulemap")
         endif()
       endif(cpp_module)
     endif()