Switch to proper wit deps handling (#10)

* guest works

* working version

* actually it's kinda works

* add some docs

.github/workflows/main.yml

@@ -0,0 +1,18 @@
+name: CI
+on:
+  push:
+    branches: [root]
+  pull_request:
+    branches: [root]
+
+jobs:
+  deps-up-to-date:
+    name: Check I2C dependency is up-to-date
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: ensure `./wit/deps` are in sync
+      run: |
+        curl -Lo 'wit-deps' https://github.com/bytecodealliance/wit-deps/releases/download/v0.3.2/wit-deps-x86_64-unknown-linux-musl
+        chmod +x ./wit-deps
+        ./wit-deps lock --check

.gitignore

@@ -1,5 +1,8 @@
 **/target
 
+# Ignore all wasm files, except the empty ones
+*.wasm
+!empty.wasm
 
 # Added by cargo
 

Justfile

@@ -0,0 +1,20 @@
+default: hat host
+
+hat: build-hat cp-hat
+lcd: build-lcd cp-lcd
+host: build-host
+
+build-hat:
+    cd guest/hat && cargo +nightly component build --release
+
+cp-hat:
+    cp guest/target/wasm32-wasi/release/hat.wasm hat.wasm
+
+build-lcd:
+    cd guest/lcd && cargo +nightly component build --release
+
+cp-lcd:
+    cp guest/target/wasm32-wasi/release/lcd.wasm lcd.wasm
+
+build-host:
+    cd host && cargo build --release --target aarch64-unknown-linux-gnu

README.md

@@ -3,6 +3,10 @@ The purpose of this repository is to serve as a proof of concept of a potential
 
 Currently, the setup is as follows: Raspberry Pi 4 Model B → I2C Interface → HD44780 LCD. It is my intention to switch out the Pi for a Pi Pico microcontroller, to have a proof of concept for a more constrained piece of hardware. I also have a Pi 3 Model B hooked up with a HTS221.
 
+## Just
+
+To make building easier [just](https://just.systems/man/en/) is used, see `Justfile`. 
+
 ## Host
 To compile for Raspberry Pi make sure to have the corresponding target and linker installed.
 
@@ -12,6 +16,12 @@ rustup target add aarch64-unknown-linux-gnu
 yay -S aarch64-linux-gnu-gcc
 ```
 
+### Switching guest
+
+1. Change the `included` guest in the wit.
+2. Change the method invocations in the `run` function inside `device.rs`.
+3. Change the used `wasm` file inside `main`.
+
 ## Guest
 ### Screen
 This guest component is written in Rust and uses the received I²C connection to display `hello world` to the HD44780 LCD screen.
@@ -32,9 +42,15 @@ cargo +nightly component build
 ```
 
 ## WIT
-`embedded.wit` comes from [hello-embedded](https://github.com/sunfishcode/hello-embedded) by sunfishcode. Only the `i2c` and `delay` interfaces are used from this.
+See [wasi-i2c](https://github.com/WebAssembly/wasi-i2c) for the source of the wit files.
+
+### `app` world and how I tried to make a generic interface for the host
+
+As I currently have multiple guest components, I would like to use whichever in the host via a CLI. Problem is that the [bindgen](https://docs.rs/wasmtime/latest/wasmtime/component/macro.bindgen.html) macro is quite restrictive, e.g. it's not possible to have one for each world or to define a wrapper around the guest components and then call that one (see [this commit](https://github.com/Zelzahn/i2c-wasm-components/pull/10/commits/5ea3c0f43e3e46022cf8d05a31e439431b359e2d)).
+
+So I came to the `app` world, it includes one of the guest components. The benefit of this wrapper is that the world itself does not change, thus limiting the number of changes required to switch the linked guest in the host.
 
-I had to use the same package for my `screen.wit` to make the `bindgen` in the host work, more specifically the `with`.
+Another solution would be to define a host for each guest component, see [this commit](https://github.com/Zelzahn/i2c-wasm-components/commit/7b9648b57c24aad50015215e89f6b6db9342f19e), but this leads to loads of code duplication.
 
 ## Embedded HAL
 The [embedded-hal](https://crates.io/crates/embedded-hal) crate is the main inspiration for the design of the API. But I currently have not found a way to package a crate that uses this API into a WASM module.

empty.wat

@@ -0,0 +1 @@
+(module)

guest/Cargo.toml

@@ -3,7 +3,7 @@ members = ["lcd", "hat"]
 resolver = "2"
 
 [workspace.dependencies]
-lol_alloc = "0.4.0"
-bitflags = "2.4.2"
+lol_alloc = "0.4.1"
+bitflags = "2.5.0"
 wit-bindgen-rt = { version = "0.22.0", default-features = false }
 compiler_builtins = { version = "0.1.108", features = ["mem"] }

guest/hat/Cargo.toml

@@ -14,19 +14,22 @@ bitflags = { workspace = true }
 wit-bindgen-rt = { workspace = true }
 compiler_builtins = { workspace = true }
 embedded-hal = "1.0.0"
-wasi-embedded-hal = { git = "https://github.com/Zelzahn/wasi-embedded-hal", default-features = false, features = [ "use_alloc" ] }
+wasi-embedded-hal = { version = "0.2.0", default-features = false, features = [
+    "use_alloc",
+] }
 
 [package.metadata.component]
-package = "embedded:hat"
+package = "sketch:implementation"
 # We don't need an adapter, but cargo-component doesn't yet have an option to
 # disable the adapter. As a workaround, use an empty adapter.
 adapter = "../empty.wasm"
 
 [package.metadata.component.target]
 path = "../../wit"
-world = "sensor"
+world = "app"
 
 [package.metadata.component.target.dependencies]
+"wasi:i2c" = { path = "../../wit/deps/i2c" }
 
 [package.metadata.component.bindings]
 # Enable this to put `std` usage behind a feature, so that we can use `no_std`.