unable to list source for <exception thrown> should never occur

[guest]

I get the very unhelpful "unable to list source for <exception thrown>". I would like to get one of the following two responses, the last one is best.

Do this and that to list source

We currently cannot list source, because you did and that Do you still want to list source                although it requires to do that and that(for example automatically recompiling and reexecuting it until the same program point) [Y/n]?

[simonmar]

Ok, would this help?

Source location of exception is unknown, try `:back` and then `:list`.

or if you're not using :trace it would suggest doing that first.

[igloo]

I've improved the error, but I'm not sure how to tell if we are running with :trace; is there an easy way?

[simonmar]

Perhaps by checking whether the history is empty?

[igloo]

Thanks; now fixed in 6.8 branch and HEAD, modulo #2054.

[igloo]

Ah, so actually the :trace detection doesn't work if you :trace an already evaluated CAF, so sometimes the error will tell you to use :trace when you already are doing.

[morabbin]

Bump; what's the state of :trace detection now?