[hageboeck]

There were way too many CI failures due to pycache being rebuilt. This e.g. prevents the doxygen documentation from building.

I'm not sure why this is happening, but CMake definitely decided that the stamp file for the python sources was out of date and rebuilt it. This change will be unnecessary if the root cause is found.

https://github.com/root-project/root/actions/runs/35296070609/job/105536700225

[guitargeek]

Thanks! But can we try #23411 first maybe? It's possible that copy_if_different gives false negatives because of files only differing in timestamp, and it's not really necessary in that ROOT_PYTHON_PACKAGE macro because the copy command is already wrapped in a add_custom_command that is only executed if the sources change (because it depends on DEPENDS ${py_sources_in_source_dir})

I didn't think that case through when introducing the ROOT_PYTHON_PACKAGE macro some months ago, but it can still be improved!

[hageboeck]

It's possible that copy_if_different gives false negatives because of files only differing in timestamp, and it's not really necessary in that ROOT_PYTHON_PACKAGE macro because the copy command is already wrapped in a add_custom_command that is only executed if the sources change (because it depends on DEPENDS ${py_sources_in_source_dir})

It's doing what it promises it does, but indeed, since the subsequent command depends on files in the build tree, the copy command must update all files in the build tree. It looks like #23411 should indeed solve that!