Small config bug in autotvm

@comaniac in my case it happened when I was logging the config at the top of a compute / schedule function, before all knobs were defined, which is sometimes useful given the dual collect / apply behavior of config.

Make sense. That’s also the only case I can think of.

True, but on subsequent calls to the same compute / schedule functions config is a ConfigEntity which has _collect always false, no?

I see. Your solution prevents ConfigEntity from calculating the length. It also works, but just a bit indirect.

Thanks for the discussion. Would you mind sending a PR to fix this?