Add first version of targets command

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

Author: rylev

Cargo.lock

@@ -40,6 +40,8 @@ indexmap = { workspace = true }
 miette = { workspace = true, features = ["fancy"] }
 semver = { workspace = true }
 indicatif = { workspace = true, optional = true }
+wit-parser = { workspace = true }
+wit-component = { workspace = true }
 
 [features]
 default = ["wit", "registry"]

Cargo.toml

@@ -100,6 +100,7 @@ The `wac` CLI tool has the following commands:
 
 * `wac plug` - Plugs the imports of a component with one or more other components.
 * `wac compose` - Compose WebAssembly components using the provided WAC source file.
+* `wac targets` - Determines whether a given component conforms to the supplied wit world.
 * `wac parse` - Parses a composition into a JSON representation of the AST.
 * `wac resolve` - Resolves a composition into a JSON representation.
 
@@ -117,6 +118,17 @@ Or mixing in packages published to a Warg registry:
 wac plug my-namespace:package-name --plug some-namespace:other-package-name -o plugged.wasm
 ```
 
+### Checking Whether a Component Implements a World
+
+To see whether a given component implements a given world, use the `wac targets` command:
+
+```
+wac targets my-component.wasm my-wit.wit
+```
+
+If `my-component.wasm` implements the world defined in `my-wit.wit` then the command will succeed. Otherwise, an error will be returned.
+
+If `my-wit.wit` has multiple world definitions, you can disambiguate using the `--world` flag.
 
 ### Encoding Compositions
 

README.md

@@ -1,7 +1,9 @@
 use anyhow::Result;
 use clap::Parser;
 use owo_colors::{OwoColorize, Stream, Style};
-use wac_cli::commands::{ComposeCommand, ParseCommand, PlugCommand, ResolveCommand};
+use wac_cli::commands::{
+    ComposeCommand, ParseCommand, PlugCommand, ResolveCommand, TargetsCommand,
+};
 
 fn version() -> &'static str {
     option_env!("CARGO_VERSION_INFO").unwrap_or(env!("CARGO_PKG_VERSION"))
@@ -21,6 +23,7 @@ enum Wac {
     Compose(ComposeCommand),
     Parse(ParseCommand),
     Resolve(ResolveCommand),
+    Targets(TargetsCommand),
 }
 
 #[tokio::main]
@@ -32,6 +35,7 @@ async fn main() -> Result<()> {
         Wac::Resolve(cmd) => cmd.exec().await,
         Wac::Compose(cmd) => cmd.exec().await,
         Wac::Plug(cmd) => cmd.exec().await,
+        Wac::Targets(cmd) => cmd.exec().await,
     } {
         eprintln!(
             "{error}: {e:?}",

src/bin/wac.rs

@@ -4,8 +4,10 @@ mod compose;
 mod parse;
 mod plug;
 mod resolve;
+mod targets;
 
 pub use self::compose::*;
 pub use self::parse::*;
 pub use self::plug::*;
 pub use self::resolve::*;
+pub use self::targets::*;

src/commands.rs

@@ -0,0 +1,197 @@
+use anyhow::{bail, Context, Result};
+use clap::Args;
+use std::{
+    fs,
+    path::{Path, PathBuf},
+};
+use wac_types::{ExternKind, ItemKind, Package, SubtypeChecker, Types, WorldId};
+
+/// Parses a WAC source file into a JSON AST representation.
+#[derive(Args)]
+#[clap(disable_version_flag = true)]
+pub struct TargetsCommand {
+    /// The path to the component
+    #[clap(value_name = "COMPONENT_PATH")]
+    pub component: PathBuf,
+    /// The path to the WIT definition
+    #[clap(value_name = "WIT_PATH")]
+    pub wit: PathBuf,
+    /// The name of the world to target
+    ///
+    /// If the wit package only has one world definition, this does not need to be specified.
+    #[clap(long)]
+    pub world: Option<String>,
+}
+
+impl TargetsCommand {
+    /// Executes the command.
+    pub async fn exec(self) -> Result<()> {
+        log::debug!("executing targets command");
+        let mut types = Types::default();
+
+        let wit_bytes = encode_wit_as_component(&self.wit)?;
+        let wit = Package::from_bytes("wit", None, wit_bytes, &mut types)?;
+
+        let component_bytes = fs::read(&self.component).with_context(|| {
+            format!(
+                "failed to read file `{path}`",
+                path = self.component.display()
+            )
+        })?;
+        let component = Package::from_bytes("component", None, component_bytes, &mut types)?;
+
+        let wit = get_wit_world(&types, wit.ty(), self.world.as_deref())?;
+
+        validate_target(&types, wit, component.ty())?;
+
+        Ok(())
+    }
+}
+
+/// Gets the selected world from the component encoded WIT package
+fn get_wit_world(
+    types: &Types,
+    top_level_world: WorldId,
+    world_name: Option<&str>,
+) -> anyhow::Result<WorldId> {
+    let top_level_world = &types[top_level_world];
+    let world = match world_name {
+        Some(world_name) => top_level_world
+            .exports
+            .get(world_name)
+            .with_context(|| format!("wit package did not contain a world name '{world_name}'"))?,
+        None if top_level_world.exports.len() == 1 => {
+            top_level_world.exports.values().next().unwrap()
+        }
+        None if top_level_world.exports.len() > 1 => {
+            bail!("wit package has multiple worlds, please specify one with the --world flag")
+        }
+        None => {
+            bail!("wit package did not contain a world")
+        }
+    };
+    let ItemKind::Type(wac_types::Type::World(world_id)) = world else {
+        // We expect the top-level world to export a world type
+        bail!("wit package was not encoded properly")
+    };
+    let wit_world = &types[*world_id];
+    let world = wit_world.exports.values().next();
+    let Some(ItemKind::Component(w)) = world else {
+        // We expect the nested world type to export a component
+        bail!("wit package was not encoded properly")
+    };
+    Ok(*w)
+}
+
+/// Encodes the wit package found at `path` into a component
+fn encode_wit_as_component(path: &Path) -> anyhow::Result<Vec<u8>> {
+    let mut resolve = wit_parser::Resolve::new();
+    let pkg = if path.is_dir() {
+        log::debug!(
+            "loading WIT package from directory `{path}`",
+            path = path.display()
+        );
+
+        let (pkg, _) = resolve.push_dir(&path)?;
+        pkg
+    } else if path.extension().and_then(std::ffi::OsStr::to_str) == Some("wit") {
+        let unresolved = wit_parser::UnresolvedPackage::parse_file(&path)?;
+        let pkg = resolve.push(unresolved)?;
+        pkg
+    } else {
+        bail!("expected either a wit directory or wit file")
+    };
+    let encoded = wit_component::encode(Some(true), &resolve, pkg).with_context(|| {
+        format!(
+            "failed to encode WIT package from `{path}`",
+            path = path.display()
+        )
+    })?;
+    Ok(encoded)
+}
+
+/// An error in target validation
+#[derive(thiserror::Error, miette::Diagnostic, Debug)]
+#[diagnostic(code("component does not match wit world"))]
+pub enum Error {
+    #[error("the target wit does not have an import named `{import}` but the component does")]
+    /// The import is not in the target world
+    ImportNotInTarget {
+        /// The name of the missing target
+        import: String,
+    },
+    #[error("{kind} `{name}` has a mismatched type for targeted wit world")]
+    /// An import or export has a mismatched type for the target world.
+    TargetMismatch {
+        /// The name of the mismatched item
+        name: String,
+        /// The extern kind of the item
+        kind: ExternKind,
+        /// The source of the error
+        #[source]
+        source: anyhow::Error,
+    },
+    #[error("the targeted wit world requires an export named `{name}` but the component did not export one")]
+    /// Missing an export for the target world.
+    MissingTargetExport {
+        /// The export name.
+        name: String,
+        /// The expected item kind.
+        kind: ItemKind,
+    },
+}
+
+/// Validate whether the component conforms to the given world
+pub fn validate_target<'a>(
+    types: &'a Types,
+    wit_world_id: WorldId,
+    component_world_id: WorldId,
+) -> Result<(), Error> {
+    let component_world = &types[component_world_id];
+    let wit_world = &types[wit_world_id];
+    // The interfaces imported implicitly through uses.
+    let implicit_imported_interfaces = wit_world.implicit_imported_interfaces(types);
+    let mut cache = Default::default();
+    let mut checker = SubtypeChecker::new(&mut cache);
+
+    // The output is allowed to import a subset of the world's imports
+    checker.invert();
+    for (import, item_kind) in component_world.imports.iter() {
+        let expected = implicit_imported_interfaces
+            .get(import.as_str())
+            .or_else(|| wit_world.imports.get(import))
+            .ok_or_else(|| Error::ImportNotInTarget {
+                import: import.to_owned(),
+            })?;
+
+        checker
+            .is_subtype(expected.promote(), types, *item_kind, types)
+            .map_err(|e| Error::TargetMismatch {
+                kind: ExternKind::Import,
+                name: import.to_owned(),
+                source: e,
+            })?;
+    }
+
+    checker.revert();
+
+    // The output must export every export in the world
+    for (name, expected) in &wit_world.exports {
+        let export = component_world.exports.get(name).copied().ok_or_else(|| {
+            Error::MissingTargetExport {
+                name: name.clone(),
+                kind: *expected,
+            }
+        })?;
+
+        checker
+            .is_subtype(export, types, expected.promote(), types)
+            .map_err(|e| Error::TargetMismatch {
+                kind: ExternKind::Export,
+                name: name.clone(),
+                source: e,
+            })?;
+    }
+
+    Ok(())
+}