what does the c checked by this tool look like? for an example like https://play.rust-lang.org/?version=stable&mode=debug&editio... , does the tool accept the assignment with f and reject the assignment with g?
what do the annotations for the tool look like? is the analysis local, in that it doesn't look into the bodies of other functions? if it is, surely you would have to have lifetimes and be generic over them.
how much c code satisfies the tool? if there's hardly any c satisfying the tool, there might actually be a larger ecosystem of rust code to use.
If you want to get a sense of what that may look like, see https://www.frama-c.com (which is a community project, so maybe not as smooth and polished like more professional tools).