The idea behind RUST_CTFE_BACKTRACE=1 was that it should only show a backtrace (of where a Miri error originates) when an error is actually shown to the user. And that worked fine when I implemented it. But since then, something changed in const_prop, and now I get thousands of backtraces even for crates with no errors, making the env var basically unusable. That is a big problem for debugging of the Miri engine.

Even RUST_CTFE_BACKTRACE=immediate shouldn't show so many errors, but that will be harder to do for const_prop which runs the CTFE engine on broken and non-monomorphized MIR (causing tons of problems, not just this).

@oli-obk @wesleywiser AFAIK you did a bunch of const_prop changes over the last few weeks/months; likely some of what you did is the culprit here. Any ideas?