Add basic example of wac CLI and programatic API

Signed-off-by: Ryan Levick <ryan.levick@fermyon.com>

Author: rylev

Cargo.lock

@@ -45,6 +45,9 @@ wat = ["wac-resolver/wat"]
 wit = ["wac-resolver/wit"]
 registry = ["wac-resolver/registry", "indicatif"]
 
+[workspace]
+members = ["examples/programmatic"]
+
 [workspace.dependencies]
 wac-parser = { path = "crates/wac-parser", version = "0.1.0", default-features = false }
 wac-resolver = { path = "crates/wac-resolver", version = "0.1.0", default-features = false }
@@ -61,7 +64,10 @@ clap = { version = "4.5.4", features = ["derive"] }
 semver = { version = "1.0.22", features = ["serde"] }
 pretty_env_logger = "0.5.0"
 log = "0.4.21"
-tokio = { version = "1.37.0", default-features = false, features = ["macros", "rt-multi-thread"] }
+tokio = { version = "1.37.0", default-features = false, features = [
+    "macros",
+    "rt-multi-thread",
+] }
 owo-colors = { version = "4.0.0", features = ["supports-colors"] }
 indexmap = { version = "2.2.6", features = ["serde"] }
 id-arena = "2.2.1"

Cargo.toml

@@ -0,0 +1,55 @@
+# Examples
+
+This example is composed of two different but equal ways for composing two example components together
+* using the `wac` CLI
+* using the `wac-graph` library crate
+
+The example uses two input components (both located in the `deps` directory) that will be composed together:
+
+The `hello` component exports a function `hello` which returns a string:
+
+```bash
+# Print the wit for the hello component
+$ wasm-tools component wit deps/example/hello.wasm 
+package root:component;
+
+world root {
+  export hello: func() -> string;
+}
+```
+
+The `hello` exported function from `hello.wasm` will be plugged into the `hello` import of the `greeter` component which has the same signature as the `hello` exported function: 
+
+```bash
+# Print the wit for the greeter component
+$ wasm-tools component wit deps/example/greeter.wasm 
+package root:component;
+
+world root {
+  import hello: func() -> string;
+
+  export greet: func() -> string;
+}
+```
+
+The resulting composed component will therefore only have the exported `greet` function originally from the `greeter` component.
+
+## CLI
+
+`wac` can be used as a CLI tool. The `wac encode` command takes a wac script as input which defines how two components are composed together.
+
+Running the following command should produce a new component that is the composition of the `hello` and `greeter` components.
+
+```
+wac encode composition.wac -o composed.wasm  
+```
+
+*Note*: `wac encode` expects to find any input components inside of a `deps` folder in a directory named after the namespace part of the input component's name. In our example, the wac script uses the `example:greeter` and `example:hello` input components so `wac encode` expects to find those components in the `deps/example` directory.
+
+## Programmatic Graph API
+
+You can also build the composition using the programmatic API used by the `programmatic` example binary. This can be done by running the following inside the `programmatic` directory:
+
+```
+$ cargo run
+```

examples/README.md

@@ -0,0 +1,7 @@
+[package]
+name = "programmatic-example"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+wac-graph = { path = "../../crates/wac-graph" }

examples/deps/example/greeter.wasm

@@ -0,0 +1,46 @@
+use wac_graph::{types::Package, CompositionGraph, EncodeOptions};
+
+fn main() {
+    let mut graph = CompositionGraph::new();
+
+    // Register the package dependencies into the graph
+    let package = Package::from_file(
+        "hello",
+        None,
+        "../deps/example/hello.wasm",
+        graph.types_mut(),
+    )
+    .unwrap();
+    let hello = graph.register_package(package).unwrap();
+    let package = Package::from_file(
+        "greeter",
+        None,
+        "../deps/example/greeter.wasm",
+        graph.types_mut(),
+    )
+    .unwrap();
+    let greeter = graph.register_package(package).unwrap();
+
+    // Instantiate the hello instance which does not have any arguments
+    let hello_instance = graph.instantiate(hello);
+
+    // Instantiate the greeter instance which has a single argument "hello" which is exported by the hello instance
+    let greeter_instance = graph.instantiate(greeter);
+    let hello_export = graph
+        .alias_instance_export(hello_instance, "hello")
+        .unwrap();
+    graph
+        .set_instantiation_argument(greeter_instance, "hello", hello_export)
+        .unwrap();
+
+    // Alias the "greet" export from the greeter instance
+    let greet_export = graph
+        .alias_instance_export(greeter_instance, "greet")
+        .unwrap();
+    // Export the "greet" function from the composition
+    graph.export(greet_export, "greet").unwrap();
+
+    // Encode the graph into a WASM binary
+    let encoding = graph.encode(EncodeOptions::default()).unwrap();
+    std::fs::write("composition.wasm", encoding).unwrap();
+}

examples/deps/example/hello.wasm

@@ -0,0 +1,13 @@
+package example:composition;
+
+// Instantiate the `hello` component
+let hello = new example:hello {};
+
+// Instantiate the `greeter` component plugging its one `hello` import with 
+// the `hello` export of the `hello` component.
+let greeter = new example:greeter {
+  hello: hello.hello,
+};
+
+// Export the greet function from the greeter component
+export greeter.greet;