[core] Add core headers to private CMake target FILE_SETS

[ferdymercury]

This is a non-functional change, it only improves the IDE experience.

In the future, we could avoid copying headers to build-directory and verbose target_include_directory statements by just using the file_sets. Same with INSTALL, would go through headers.
This could ultimately go into the ROOT custom macros, but for the moment let's only do the minimal changes for the IDE and let the rest for later.
They are all added as private now, in the future we can distinguish private from public file-sets.
As well as DICT_HEADERS for dictionary generation. This might enhance dependency issues and build speed.

Follow-up of #18419

[guitargeek]

Hi! Can this not be part of the ROOT_STANDARD_LIBRARY_PACKAGE, so we don't duplicate a lot of CMake configuration code?

[ferdymercury]

Hi! Can this not be part of the ROOT_STANDARD_LIBRARY_PACKAGE, so we don't duplicate a lot of CMake configuration code?

Not without a major rework of that macro as well as other macro such as ROOT_OBJECT_LIBRARY, since we have to specify separately DICT_HEADERS vs public headers not in dict vs private headers. Then we would also need to specify the base directory of each group of headers (inc, res)...
As said in the first message, I agree that this is the way to go, but I don't think I can achieve that myself since I am not expert with it. Also, if we touch the macro, then it's difficult to add this modularly.

In my opinion, it would make sense to first add all HEADERS verbosely, which is easy and modular, and one does not risk to break everything, to improve IDE experience in a short time frame. To me, it only makes sense to touch the macros at the same time than the copy-header-to-build-dir is removed by using file-sets instead. But that's a major cleanup of the CMake build system.

Also, there are several places were headers are not explicitly stated but globbed/searched for in inc-dir, so this fixes that too.

[guitargeek]

Hi @ferdymercury, sorry for not reading your initial post carefully enough!

I think even if we can't integrate the it in the existing macros like ROOT_STANDARD_LIBRARY_PACKAGE, we should at least introduce a new macro like ROOT_SET_TARGET_SOURCES to avoid the redundant CMAKE_VERSION check and to make sure that we can find all packages that already set the target sources with git grep. That would be important if we want to merge this later at some point with ROOT_STANDARD_LIBRARY_PACKAGE/ROOT_OBJECT_LIBRARY.

What do you think?

[ferdymercury]

Thanks @guitargeek

What do you think?

I guess the answer depends on whether #19941 is going to get merged for 6.40 or for later. If we want to stay with CMake 3.22 for ROOT 6.40, then yes, it makes total sense to have ROOT_SET_TARGET_SOURCES
If not, I do not see much advantage in an extra wrapper.

Side note: one could even think the other way round for the future.

CMake target_sources defines four types of FILE_SETS

• private headers
• dictionary headers
• Linkdefs
• public headers

Then, ROOT_STL_PACKAGE would look for Target.LinkDefFileSet Target.DictHeaders

rather than passing all the headers again to ROOT_STL_PACKAGE as argument.