Target wasm32-wasi by default.

This commit makes `cargo component` target `wasm32-wasi` by default, using a
local preview1 adapter to adapt to a preview2 version of WASI.

Closes bytecodealliance#48.

.github/workflows/main.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - name: Install Rust
-      run: rustup update stable --no-self-update && rustup default stable && rustup target add wasm32-unknown-unknown
+      run: rustup update stable --no-self-update && rustup default stable && rustup target add wasm32-wasi && rustup target add wasm32-unknown-unknown
       shell: bash
     - name: Install Protobuf Compiler
       uses: arduino/setup-protoc@v1
@@ -33,7 +33,7 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - name: Install Rust
-      run: rustup update stable --no-self-update && rustup default stable && rustup target add wasm32-unknown-unknown
+      run: rustup update stable --no-self-update && rustup default stable && rustup target add wasm32-wasi && rustup target add wasm32-unknown-unknown
     - name: Install Protobuf Compiler
       uses: arduino/setup-protoc@v1
       with:

README.md

@@ -139,15 +139,25 @@ and tooling developers can use to test their implementations.
 
 ## WASI Support
 
-The current WASI preview does not yet support the WebAssembly component model.
+Currently `cargo component` targets `wasm32-wasi` by default.
 
-For that reason, `cargo component` currently targets `wasm32-unknown-unknown`
-by default.
+As this target is for a _preview1_ release of WASI, the WebAssembly module 
+produced by the Rust compiler must be adapted to the _preview2_ version of WASI 
+supported by the component model.
 
-Once a WASI preview is available that [supports the component model][1], `cargo component`
-will target WASI by default at that time.
+The adaptation is automatically performed when `wasm32-wasi` is targeted.
 
-[1]: https://github.com/WebAssembly/meetings/blob/main/wasi/2022/presentations/2022-06-30-gohman-wasi-preview2.pdf
+To prevent this, override the target to `wasm32-unknown-unknown` using the 
+`--target` option when building. This, however, will disable WASI support.
+
+Use the _preview2_ version of [`wasi-common`][2] in your host to run components 
+produced by `cargo component`.
+
+When the Rust compiler supports a [_preview2_ version of the WASI target][1], 
+support in `cargo component` for adapting a _preview1_ module will be removed.
+
+[1]: https://github.com/rust-lang/compiler-team/issues/594
+[2]: https://github.com/bytecodealliance/preview2-prototyping/tree/main/wasi-common
 
 ## Installation
 

example/README.md

@@ -19,7 +19,7 @@ To build the component, run the following command:
 cargo component build
 ```
 
-The component should now exist at `target/wasm32-unknown-unknown/debug/service.wasm`.
+The component should now exist at `target/wasm32-wasi/debug/service.wasm`.
 
 The resulting component will have the following imports:
 

src/commands.rs

@@ -150,8 +150,8 @@ impl CompileOptions {
         let spec = Packages::from_flags(self.workspace, self.exclude, self.packages)?;
 
         if self.targets.is_empty() {
-            target::install_wasm32_unknown_unknown()?;
-            self.targets.push("wasm32-unknown-unknown".to_string());
+            target::install_wasm32_wasi()?;
+            self.targets.push("wasm32-wasi".to_string());
         }
 
         log::debug!("using targets {:#?}", self.targets);

src/commands/build.rs

@@ -50,7 +50,7 @@ pub struct BuildCommand {
     #[clap(long = "no-default-features")]
     pub no_default_features: bool,
 
-    /// Build for the target triple (defaults to `wasm32-unknown-unknown`)
+    /// Build for the target triple (defaults to `wasm32-wasi`)
     #[clap(long = "target", value_name = "TRIPLE")]
     pub targets: Vec<String>,
 

src/commands/check.rs

@@ -82,7 +82,7 @@ pub struct CheckCommand {
     #[clap(long = "no-default-features")]
     pub no_default_features: bool,
 
-    /// Check for the target triple (defaults to `wasm32-unknown-unknown`)
+    /// Check for the target triple (defaults to `wasm32-wasi`)
     #[clap(long = "target", value_name = "TRIPLE")]
     pub targets: Vec<String>,
 

src/lib.rs

@@ -232,7 +232,13 @@ fn create_component(config: &Config, target_path: &Path) -> Result<()> {
         format!("component {path}", path = target_path.display()),
     )?;
 
-    let encoder = ComponentEncoder::default().module(&module)?.validate(true);
+    let encoder = ComponentEncoder::default()
+        .adapter(
+            "wasi_snapshot_preview1",
+            include_bytes!("../adapters/wasi_snapshot_preview1.wasm"),
+        )?
+        .module(&module)?
+        .validate(true);
 
     let mut producers = wasm_metadata::Producers::empty();
     producers.add(

src/target.rs

@@ -5,31 +5,31 @@ use std::{
     process::{Command, Stdio},
 };
 
-pub fn install_wasm32_unknown_unknown() -> Result<()> {
+pub fn install_wasm32_wasi() -> Result<()> {
     let sysroot = get_sysroot()?;
-    if sysroot.join("lib/rustlib/wasm32-unknown-unknown").exists() {
+    if sysroot.join("lib/rustlib/wasm32-wasi").exists() {
         return Ok(());
     }
 
     if env::var_os("RUSTUP_TOOLCHAIN").is_none() {
         bail!(
-            "failed to find the `wasm32-unknown-unknown` target \
+            "failed to find the `wasm32-wasi` target \
                and `rustup` is not available. If you're using rustup \
                make sure that it's correctly installed; if not, make sure to \
-               install the `wasm32-unknown-unknown` target before using this command"
+               install the `wasm32-wasi` target before using this command"
         );
     }
 
     let output = Command::new("rustup")
         .arg("target")
         .arg("add")
-        .arg("wasm32-unknown-unknown")
+        .arg("wasm32-wasi")
         .stderr(Stdio::inherit())
         .stdout(Stdio::inherit())
         .output()?;
 
     if !output.status.success() {
-        bail!("failed to install the `wasm32-unknown-unknown` target");
+        bail!("failed to install the `wasm32-wasi` target");
     }
 
     Ok(())

tests/build.rs

@@ -147,3 +147,23 @@ fn it_adds_a_producers_field() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn it_builds_wasm32_unknown_unknown() -> Result<()> {
+    let project = Project::new("foo")?;
+    project
+        .cargo_component("build --target wasm32-unknown-unknown")
+        .assert()
+        .stderr(contains("Finished dev [unoptimized + debuginfo] target(s)"))
+        .success();
+
+    validate_component(
+        &project
+            .build_dir()
+            .join("wasm32-unknown-unknown")
+            .join("debug")
+            .join("foo.wasm"),
+    )?;
+
+    Ok(())
+}

tests/support/mod.rs

@@ -127,14 +127,14 @@ impl Project {
 
     pub fn debug_wasm(&self, name: &str) -> PathBuf {
         self.build_dir()
-            .join("wasm32-unknown-unknown")
+            .join("wasm32-wasi")
             .join("debug")
             .join(format!("{name}.wasm"))
     }
 
     pub fn release_wasm(&self, name: &str) -> PathBuf {
         self.build_dir()
-            .join("wasm32-unknown-unknown")
+            .join("wasm32-wasi")
             .join("release")
             .join(format!("{name}.wasm"))
     }