Reimplement wasmtime-wasi on top of wasmtime (#899)

* Reimplement `wasmtime-wasi` on top of `wasmtime`

This commit reimplements the `wasmtime-wasi` crate on top of the
`wasmtime` API crate, instead of being placed on top of the `wasmtime-*`
family of internal crates. The purpose here is to continue to exercise
the API as well as avoid usage of internals wherever possible and
instead use the safe API as much as possible.

The `wasmtime-wasi` crate's API has been updated as part of this PR as
well. The general outline of it is now:

* Each module snapshot has a `WasiCtxBuilder`, `WasiCtx`, and `Wasi`
  type.
  * The `WasiCtx*` types are reexported from `wasi-common`.
  * The `Wasi` type is synthesized by the `wig` crate's procedural macro
* The `Wasi` type exposes one constructor which takes a `Store` and a
  `WasiCtx`, and produces a `Wasi`
* Each `Wasi` struct fields for all the exported functions in that wasi
  module. They're all public an they all have type `wasmtime::Func`
* The `Wasi` type has a `get_export` method to fetch an struct field by
  name.

The intention here is that we can continue to make progress on #727 by
integrating WASI construction into the `Instance::new` experience, but
it requires everything to be part of the same system!

The main oddity required by the `wasmtime-wasi` crate is that it needs
access to the caller's `memory` export, if any. This is currently done
with a bit of a hack and is expected to go away once interface types are
more fully baked in.

* Remove now no-longer-necessary APIs from `wasmtime`

* rustfmt

* Rename to from_abi

crates/misc/py/Cargo.toml

@@ -18,9 +18,7 @@ doc = false
 
 [dependencies]
 wasmtime = { path = "../../api", version = "0.9.0" }
-wasmtime-environ = { path = "../../environ", version = "0.9.0" }
 wasmtime-interface-types = { path = "../../interface-types", version = "0.9.0" }
-wasmtime-runtime = { path = "../../runtime", version = "0.9.0" }
 wasmtime-wasi = { path = "../../wasi", version = "0.9.0" }
 target-lexicon = { version = "0.10.0", default-features = false }
 anyhow = "1.0.19"

crates/misc/py/src/lib.rs

@@ -89,9 +89,11 @@ pub fn instantiate(
     // If this module expects to be able to use wasi then go ahead and hook
     // that up into the imported crates.
     let wasi = if let Some(module_name) = data.find_wasi_module_name() {
-        let instance = wasmtime_wasi::create_wasi_instance(&store, &[], &[], &[])
+        let cx = wasmtime_wasi::WasiCtxBuilder::new()
+            .build()
             .map_err(|e| err2py(e.into()))?;
-        Some((module_name, instance))
+        let wasi = wasmtime_wasi::Wasi::new(&store, cx);
+        Some((module_name, wasi))
     } else {
         None
     };
@@ -111,7 +113,7 @@ pub fn instantiate(
                 .ok_or_else(|| {
                     PyErr::new::<Exception, _>(format!("wasi export {} is not found", i.name(),))
                 })?;
-            imports.push(e.clone());
+            imports.push(e.clone().into());
         } else {
             return Err(PyErr::new::<Exception, _>(format!(
                 "imported module {} is not found",

crates/misc/rust/macro/src/lib.rs

@@ -62,14 +62,14 @@ fn generate_load(item: &syn::ItemTrait) -> syn::Result<TokenStream> {
 
             let mut imports: Vec<Extern> = Vec::new();
             if let Some(module_name) = data.find_wasi_module_name() {
-                let wasi_instance = #root::wasmtime_wasi::create_wasi_instance(&store, &[], &[], &[])
-                    .map_err(|e| format_err!("wasm instantiation error: {:?}", e))?;
+                let wasi_cx = #root::wasmtime_wasi::WasiCtxBuilder::new().build()?;
+                let wasi = #root::wasmtime_wasi::Wasi::new(&store, wasi_cx);
                 for i in module.imports().iter() {
                     if i.module() != module_name {
                         bail!("unknown import module {}", i.module());
                     }
-                    if let Some(export) = wasi_instance.get_export(i.name()) {
-                        imports.push(export.clone());
+                    if let Some(export) = wasi.get_export(i.name()) {
+                        imports.push(export.clone().into());
                     } else {
                         bail!("unknown import {}:{}", i.module(), i.name())
                     }