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[cmake] Drop CMake's cached DEPFILE list after generating a dictionary #23876

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Merged
dpiparo merged 1 commit into from
Oct 28, 2026
Merged

[cmake] Drop CMake's cached DEPFILE list after generating a dictionary #23876

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17 changes: 17 additions & 0 deletions cmake/modules/RootMacros.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -773,6 +773,22 @@ function(ROOT_GENERATE_DICTIONARY dictionary)
set(touch_byproducts_command COMMAND ${CMAKE_COMMAND} -E touch_nocreate ${dictionary_byproducts})
endif()

# The Makefile generators of CMake < 4.0 merge the entries of a custom
# command's DEPFILE into CMakeFiles/<target>.dir/compiler_depend.internal
# instead of replacing them (CMake issue 26399). A header, LinkDef or pcm
# that rootcling read once but that has since disappeared, e.g. because the
# build tree is reused across a checkout, then stays recorded as a missing
# prerequisite, and make regenerates the dictionary on every build. Dropping
# the cached list after rootcling has run makes the next dependency scan
# start from the fresh depfile only, as CMake itself does for library
# targets whenever it regenerates.
set(drop_cached_depends_command)
if(CMAKE_GENERATOR MATCHES "Makefiles" AND CMAKE_VERSION VERSION_LESS 4.0)
get_filename_component(dictionary_target ${dictionary} NAME)
set(drop_cached_depends_command COMMAND ${CMAKE_COMMAND} -E rm -f
${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/${dictionary_target}.dir/compiler_depend.internal)
endif()

#---call rootcling------------------------------------------
add_custom_command(
OUTPUT ${dictionary}.cxx ${pcm_name} ${rootmap_name} ${cpp_module_file}
Expand All @@ -789,6 +805,7 @@ function(ROOT_GENERATE_DICTIONARY dictionary)
-DR__DUMMY_CXX_STANDARD_${CMAKE_CXX_STANDARD}
-MF ${depfile_path}
${touch_byproducts_command}
${drop_cached_depends_command}
DEPFILE ${depfile_path}
DEPENDS ${_list_of_header_dependencies} ${_linkdef} ${ROOTCLINGDEP}
${pcm_dependencies}
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