Fuzzing the Erlang ecosystem

Erlfuzz is a recently open-sourced tool that produces random valid Erlang programs, used to test erlc, the BEAM VM, and a variety of other tools (dialyzer, eqWAlizer, erlfmt, infer, etc..). It has found more than 80 bugs to date, including more than 60 bugs in erlc. In this talk I'll explain how erlfuzz works, what tricks were used to detect subtle VM bugs, and how to use it for any tool you may want to test. I'll also mention some of the dark corners of the language that it revealed, mostly around the Erlang scoping rules.