This is enough to get an `externref -> externref` identity function passing. However, `externref`s that are dropped by compiled Wasm code are (safely) leaked. Follow up work will leverage cranelift's stack maps to resolve this issue.
This is the wasmtime-wast crate, which contains an implementation of WebAssembly's
"wast" test scripting language, which is used in the
WebAssembly spec testsuite, using wasmtime for execution.