rust-analyzer could probably do it. That information isn't exposed in type signatures, though, so it'd have to have full access to the source of everything and

rust-analyzer could probably do it. That information isn't exposed in type signatures, though, so it'd have to have full access to the source of everything and a good understanding of the standard library (and would fail if you added your own “might allocate” by going around the back of the global allocator).