`typeof(ref)` shown on stdout

[c42f]

I just got the following inscrutable message on stdout while using Revise, and tracked it to LoweredCodeUtils:

ref = :(_1)
typeof(ref) = Core.SlotNumber

Presumably this was emitted by the line here: https://github.com/JuliaDebug/LoweredCodeUtils.jl/blob/ff8998f6151bce37bbf6a82ce72622e692fd8df3/src/signatures.jl#L412

Strangely this doesn't seem to have triggered the assert on the next line (or if it did, the error was swallowed somewhere, because I didn't see an AssertionError).

[c42f]

So far I've only observed this a single time, but I'll post a reproducer if I find one.

[c42f]

I've seen this more than once now, but still no idea what causes it.

[timholy]

Maybe dev LoweredCodeUtils and add a few additional things to @show: bodyparent JuliaInterpreter.whereis(frame)?