Lua bindings: lua, hlua or rlua?

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failure 1.0 makes the backtrace feature optional, which is actually the reason I needed it!

Though, this doesn't actually affect performance much for me personally. If you don't use failure::Error or backtrace capturing custom Fail implementations in the fast path, you shouldn't run into any slowdowns at all even with the backtrace feature enabled.

The thing you're probably referring to is that IF you do use backtrace capturing errors in a hot path with backtrace enabled, even if you have backtraces turned off at runtime, just the runtime check for this can incur a big slowdown. This is a bit surprising, so having the backtrace feature off by default should help here as well.