The failure crate invents its own traits that don't use std::error::Error (because failure predates certain features added to Error); this prevents using ? on an error from failure in a function using Error. The thiserror crate integrates with the standard Error trait instead.
This crate performs the translation from a wasm module in binary format to the in-memory form of the Cranelift IR.
If you're looking for a complete WebAssembly implementation that uses this library, see Wasmtime.