Add example wasm component and runner which embeds the component

.gitignore

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+/target
+bindings.rs

Cargo.toml

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+[workspace]
+
+members = [
+    "component",
+    "runner",
+]

README.md

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+# Wasmtime test
+
+Example project showcasing how to run a wasm component with wasmtime, and how to build the runnable component using cargo component.
+
+## Structure
+
+### component
+
+This package includes an example wasm component, which simply calls a `hello()` function provided by the runner.
+
+### runner
+
+This package includes an example runtime, to run the built wasm component from the component package.
+
+## Build
+
+First run `cargo component build -p component --release` to build the wasm component.
+
+Then run `cargo run -p runner --release` to run the runner with the build wasm component from the previous step.
+
+## Troubleshooting
+
+If you see errors about imports missing when trying to run the compiled component, it's likely there's a dependency on std that isn't supported by the runtime linker (e.g. by calling `println!()`).
+To build without std components, run the following:
+
+`cargo component build --target wasm32-unknown-unknown --release`
+
+Note this is only required when using std components. Preferably don't do this, and instead
+use #![no_std] to not accidentally use std. Otherwise, you'll need to either use a runtime that includes std (e.g. wasmtime cli), or add the appropriate imports to the runtime linker.
+
+To check the imports and exports for a compiled .wasm component, run the following (where component.wasm is the compiled .wasm file to inspect):
+
+`wasm-tools component wit component.wasm`

component/Cargo.toml

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+[package]
+name = "component"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+wit-bindgen-rt = { version = "0.24.0", features = ["bitflags"] }
+
+[lib]
+crate-type = ["cdylib"]
+
+[package.metadata.component]
+package = "component:test"

component/src/lib.rs

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+#[allow(warnings)]
+mod bindings;
+
+use bindings::{hello, Guest};
+
+struct Component;
+
+impl Guest for Component {
+    fn greet() {
+        hello();
+    }
+}
+
+bindings::export!(Component with_types_in bindings);

component/wit/test.wit

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+package my:project;
+
+world test {
+    import hello: func();
+    export greet: func();
+}

runner/Cargo.toml

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+[package]
+name = "wasmtime-test"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+wasmtime = {version = "20.0.2", features = ["component-model"]}

runner/src/main.rs

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+use wasmtime::{
+    component::{bindgen, Component, Linker},
+    Config, Engine, Store,
+};
+
+// Defaults to 'wit' folder adjacent to cargo.toml.
+// Change folder by using: bindgen!(in "other/with/folder")
+bindgen!();
+
+struct TestState {
+    name: String,
+}
+
+impl TestImports for TestState {
+    fn hello(&mut self) -> std::result::Result<(), wasmtime::Error> {
+        println!("{}", self.name);
+        Ok(())
+    }
+}
+
+fn main() -> wasmtime::Result<()> {
+    let mut config = Config::new();
+    config.wasm_component_model(true);
+    let engine = Engine::new(&config)?;
+    let component = Component::from_file(&engine, "target/wasm32-wasi/release/component.wasm")?;
+    let mut linker = Linker::new(&engine);
+    Test::add_to_linker(&mut linker, |state: &mut TestState| state)?;
+    let mut store = Store::new(
+        &engine,
+        TestState {
+            name: "Hello World".to_string(),
+        },
+    );
+    let (bindings, _) = Test::instantiate(&mut store, &component, &linker)?;
+    bindings.call_greet(&mut store)?;
+    Ok(())
+}

runner/wit/test.wit

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+package my:project;
+
+world test {
+    import hello: func();
+    export greet: func();
+}