Currently, source_group() is restricted to subdirectories, which is not convenient then we have a base library with sets of headers (inside some target possibly).
While we could use the `target_sources( INTERFACE) for adding some headers/file sets, we can’t group it in a target itself.
It would be convenient if we could also optionally store the source_groups inside the targets and derive it as a property.
The source_group functionality is one of the last few pieces of the older directory-based model that hasn’t been updated to target-based equivalents. I agree with (2) in the original post that target_sources may be a reasonable place to specify source groups.
I expect people will want to control source groups both for normal sources and those in a FILE_SET, and perhaps map sources in the same file set to multiple different source groups.