It's valuable information, including to the user, since it may point to a very specific part of the code (before they even report the ICE to us), and it's always available (even without debuginfo).

We could even print the query stack like a set of diagnostic messages, highlighting the span that was provided with tcx.at(span) (if any) - I guess we have the code for it, for query cycles?

cc @rust-lang/compiler