A destructor that fails when run from the cycle collector will do terrible things

[brson]

Failing inside a destructor is broken to begin with, but failing from within the cycle collector is even worse:

1. The cycle collector won't catch the failure and continue
2. The cycle collector jumps from the C stack to the Rust stack to run the destructor but does not do the proper maintenance if the destructor throws
3. The logic that prevents failure in crust functions is in effect because of reentry into the Rust stack, so the runtime will abort
4. The final cycle collection happens outside of any try-catch block so the runtime will abort

[catamorphism]

Also see: #910

[brson]

This needs to be revisited now that the cc is done in Rust code. The situation may not be as bad.

[pcwalton]

The cycle collector has been nuked from orbit.