Remove non-WASI code

crates/plugin_runtime/README.md

@@ -1,6 +1,48 @@
 # Zed's Plugin Runner
-This crate contains a fairly generic interface through which plugins may be added to extend the editor. Currently the intention of this plugin runtime is language server definitions.
+Wasm plugins can be run through `wasmtime`, with supported for sandboxed system integration through WASI. There are three `plugin` crates that implement different things:
 
-Anything that implements the `Runtime` trait may be used as a plugin. Plugin interfaces are declared by implementing the `Interface` trait.
+1. `plugin_runtime` loads and runs compiled `Wasm` plugins, and handles setting up system bindings.
 
-Wasm plugins can be run through `wasmtime`. We plan to add wasi support eventually. We also plan to add macros to generate bindings between Rust plugins compiled to Wasm and the host runtime.
+2. `plugin` is the crate that Rust Wasm plugins should depend on. It re-exports some required crates (e.g. `serde`, `bincode`) and provides some necessary macros for generating bindings that `plugin_runtime` can hook into.
+
+3. `plugin_macros` implements the proc macros required by `plugin`, like the `#[bind]` attribute macro.
+
+## ABI
+The interface between the host Rust runtime ('Runtime') and plugins implemented in Wasm ('Plugin') is pretty simple.
+
+`Buffer` is a pair of two 4-byte (`u32`) fields:
+
+```
+struct Buffer {
+    ptr: u32,
+    len: u32,
+}
+```
+
+All functions that Plugin exports must have the following properties:
+
+- Have the signature `fn(ptr: u32, len: u32) -> u32`, where the return type is a pointer to a `Buffer`, and the arguments are the component parts of a `Buffer`.
+
+    - The input `Buffer` will contain the input arguments serialized to `bincode`.
+    - The output `Buffer` will contain the output arguments serialized to `bincode`.
+
+- Have a name starting with two underscores.
+
+Additionally, Plugin must export an:
+
+- `__alloc_buffer` function that, given a `u32` length, returns a `u32` pointer to a buffer of that length.
+
+Note that all of these requirements are automatically fullfilled for any Rust Wasm plugin that uses the `plugin` crate, and imports the `prelude`. 
+
+Here's an example Rust Wasm plugin that doubles the value of every float in a `Vec<f64>` passed into it:
+
+```rust
+use plugin::prelude::*;
+
+#[bind]
+pub fn double(mut x: Vec<f64>) -> Vec<f64> {
+    x.into_iter().map(|x| x * 2.0).collect()
+}
+```
+
+All the serialization code is automatically generated by `#[bind]`.