I made an additional request for VHDL-2008 support in #12, but I'm not sure that it will be seen since the issue is closed. If it has already been seen, then please close this issue.
I've just implemented force/release so if you download the program again, that should work now.
Slices in aggregates are supposed to work. Do you have an example of a failing VHDL file?
I'm working on hierarchical names and contexts but they're a while away from being done.
I only listed slices in aggregates because I didn't see it in the list of supported features. I haven't actually used vhdl-tool very much yet. Without support for contexts, I didn't find it very useful, because I can't navigate around the code. If you've implemented it, presumably it will work.
Contexts have been implemented in version 0.12. Remaining missing VHDL-2008 features are tracked here: https://git.vhdltool.com/vhdl-tool/vhdl-tool/issues/29.