CMake: Fix ROOT dictionary dependencies of incremental builds

Author: davidrohr

cmake/AddRootDictionary.cmake

@@ -133,12 +133,23 @@ function(add_root_dictionary target)
   set(includeDirs $<REMOVE_DUPLICATES:${includeDirs}>)
 
   list(LENGTH A_EXTRA_PATCH hasExtraPatch)
+
+  set(_pcmdeps "$<REMOVE_DUPLICATES:${list_pcm_deps_${target}}>")
+  set(depSignatureFile ${CMAKE_CURRENT_BINARY_DIR}/${dictionary}_pcmdeps.txt)
+
+  file(GENERATE
+    OUTPUT ${depSignatureFile}
+    CONTENT "$<JOIN:${_pcmdeps},\n>"
+  )
+
   # add a custom command to generate the dictionary using rootcling
   # cmake-format: off
   add_custom_command(
     OUTPUT ${dictionaryFile} ${pcmFile} ${rootmapFile}
     VERBATIM
     COMMAND
+    ${CMAKE_COMMAND} -E rm -f ${dictionaryFile} ${pcmFile} ${rootmapFile}
+    COMMAND
     ${CMAKE_BINARY_DIR}/rootcling_wrapper.sh
       --rootmap_file ${rootmapFile}
       --dictionary_file ${dictionaryFile}
@@ -149,11 +160,11 @@ function(add_root_dictionary target)
       $<$<BOOL:${prop}>:-D$<JOIN:${prop},$<SEMICOLON>-D>>
       $<$<BOOL:${hasExtraPatch}>:--extra-patch>
       $<$<BOOL:${hasExtraPatch}>:${CMAKE_CURRENT_LIST_DIR}/${A_EXTRA_PATCH}>
-      --pcmdeps "$<REMOVE_DUPLICATES:${list_pcm_deps_${target}}>"
+      --pcmdeps "${_pcmdeps}"
       --headers "${headers}"
     COMMAND
     ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_BINARY_DIR}/${pcmBase} ${pcmFile}
-    DEPENDS ${headers} "$<REMOVE_DUPLICATES:${list_pcm_deps_${target}}>" ${A_EXTRA_PATCH})
+    DEPENDS ${headers} "$<REMOVE_DUPLICATES:${list_pcm_deps_${target}}>" ${depSignatureFile} ${A_EXTRA_PATCH})
   # cmake-format: on
 
   # add dictionary source to the target sources