[wahern]

Here's a potential use-after-free, listed in my query:

  https://github.com/servo/servo/issues/14014

Of course it's using unsafe code and doing other crazy stuff--a lot of these issues are related to shared, mutable, tree structures. But that's precisely my point. When you're implementing something as sophisticated as Servo and trying to keep things performant and multi-threaded, concurrency is hardly fearless. Servo does this and they have bugs.

Indeed, being "fearless" is precisely how you end up with these bugs, in Rust or any other language. If you're fearless you're more apt to move from a big lock to a fine-grained locking mechanism. That's error prone, including in Rust.

It's like that dude in Florida whose Tesla flew under the tractor trailer. He was fearless in the same way inexperienced engineers using Rust will be when they hear "fearless concurrency". They'll push the envelope when they have no need to, because that's what inexperienced engineers do who haven't been burned, especially when they think their tools make them fire-proof.