Implement the targets clause on the package directive.

LANGUAGE.md

@@ -409,7 +409,7 @@ statement ::= import-statement
             | let-statement
             | export-statement
 
-package-decl ::= `package` package-name `;`
+package-decl ::= `package` package-name (`targets` package-path)? `;`
 package-name ::= id (':' id)+ ('@' version)?
 version      ::= <SEMVER>
 

crates/wac-parser/src/ast.rs

@@ -256,6 +256,10 @@ pub(crate) trait Parse<'a>: Sized {
     fn parse(lexer: &mut Lexer<'a>) -> ParseResult<Self>;
 }
 
+trait Peek {
+    fn peek(lookahead: &mut Lookahead) -> bool;
+}
+
 fn parse_delimited<'a, T: Parse<'a> + Peek>(
     lexer: &mut Lexer<'a>,
     until: Token,
@@ -288,8 +292,25 @@ fn parse_delimited<'a, T: Parse<'a> + Peek>(
     Ok(items)
 }
 
-trait Peek {
-    fn peek(lookahead: &mut Lookahead) -> bool;
+/// Represents a package directive in the AST.
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct PackageDirective<'a> {
+    /// The name of the package named by the directive.
+    pub package: PackageName<'a>,
+    /// The optional world being targeted by the package.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub targets: Option<PackagePath<'a>>,
+}
+
+impl<'a> Parse<'a> for PackageDirective<'a> {
+    fn parse(lexer: &mut Lexer<'a>) -> ParseResult<Self> {
+        parse_token(lexer, Token::PackageKeyword)?;
+        let package = Parse::parse(lexer)?;
+        let targets = parse_optional(lexer, Token::TargetsKeyword, Parse::parse)?;
+        parse_token(lexer, Token::Semicolon)?;
+        Ok(Self { package, targets })
+    }
 }
 
 /// Represents a top-level WAC document.
@@ -298,8 +319,8 @@ trait Peek {
 pub struct Document<'a> {
     /// The doc comments for the package.
     pub docs: Vec<DocComment<'a>>,
-    /// The package name of the document.
-    pub package: PackageName<'a>,
+    /// The package directive of the document.
+    pub directive: PackageDirective<'a>,
     /// The statements in the document.
     pub statements: Vec<Statement<'a>>,
 }
@@ -312,10 +333,7 @@ impl<'a> Document<'a> {
         let mut lexer = Lexer::new(source).map_err(Error::from)?;
 
         let docs = Parse::parse(&mut lexer)?;
-
-        parse_token(&mut lexer, Token::PackageKeyword)?;
-        let package = Parse::parse(&mut lexer)?;
-        parse_token(&mut lexer, Token::Semicolon)?;
+        let directive = Parse::parse(&mut lexer)?;
 
         let mut statements: Vec<Statement> = Default::default();
         while lexer.peek().is_some() {
@@ -325,7 +343,7 @@ impl<'a> Document<'a> {
         assert!(lexer.next().is_none(), "expected all tokens to be consumed");
         Ok(Self {
             docs,
-            package,
+            directive,
             statements,
         })
     }

crates/wac-parser/src/ast/printer.rs

@@ -30,12 +30,7 @@ impl<'a, W: Write> DocumentPrinter<'a, W> {
     /// Prints the given document.
     pub fn document(&mut self, doc: &Document) -> std::fmt::Result {
         self.docs(&doc.docs)?;
-        writeln!(
-            self.writer,
-            "package {package};",
-            package = self.source(doc.package.span),
-        )?;
-        self.newline()?;
+        self.package_directive(&doc.directive)?;
 
         for (i, statement) in doc.statements.iter().enumerate() {
             if i > 0 {
@@ -49,6 +44,24 @@ impl<'a, W: Write> DocumentPrinter<'a, W> {
         Ok(())
     }
 
+    /// Prints the given package directive.
+    pub fn package_directive(&mut self, directive: &PackageDirective) -> std::fmt::Result {
+        self.indent()?;
+        write!(
+            self.writer,
+            "package {package}",
+            package = self.source(directive.package.span),
+        )?;
+
+        if let Some(targets) = &directive.targets {
+            write!(self.writer, " ")?;
+            self.package_path(targets)?;
+        }
+
+        writeln!(self.writer, ";")?;
+        self.newline()
+    }
+
     /// Prints the given statement.
     pub fn statement(&mut self, statement: &Statement) -> std::fmt::Result {
         match statement {

crates/wac-parser/src/lexer.rs

@@ -235,6 +235,9 @@ pub enum Token {
     /// The `package` keyword.
     #[token("package")]
     PackageKeyword,
+    /// The `targets` keyword.
+    #[token("targets")]
+    TargetsKeyword,
 
     /// The `;` symbol.
     #[token(";")]
@@ -338,6 +341,7 @@ impl fmt::Display for Token {
             Token::IncludeKeyword => write!(f, "`include` keyword"),
             Token::AsKeyword => write!(f, "`as` keyword"),
             Token::PackageKeyword => write!(f, "`package` keyword"),
+            Token::TargetsKeyword => write!(f, "`targets` keyword"),
             Token::Semicolon => write!(f, "`;`"),
             Token::OpenBrace => write!(f, "`{{`"),
             Token::CloseBrace => write!(f, "`}}`"),
@@ -827,6 +831,8 @@ let
 use
 include
 as
+package
+targets
             "#,
             &[
                 (Ok(Token::ImportKeyword), "import", 1..7),
@@ -866,6 +872,8 @@ as
                 (Ok(Token::UseKeyword), "use", 203..206),
                 (Ok(Token::IncludeKeyword), "include", 207..214),
                 (Ok(Token::AsKeyword), "as", 215..217),
+                (Ok(Token::PackageKeyword), "package", 218..225),
+                (Ok(Token::TargetsKeyword), "targets", 226..233),
             ],
         );
     }

crates/wac-parser/src/resolution.rs

@@ -681,6 +681,44 @@ pub enum Error {
         #[label(primary, "spreading the exports of this instance has no effect")]
         span: SourceSpan,
     },
+    /// An import is not in the target world.
+    #[error("import `{name}` is not present in target world `{world}`")]
+    ImportNotInTarget {
+        /// The import name.
+        name: String,
+        /// The target world.
+        world: String,
+        /// The span where the error occurred.
+        #[label(primary, "import `{name}` is not in the target world")]
+        span: SourceSpan,
+    },
+    /// Missing an export for the target world.
+    #[error("missing export `{name}` for target world `{world}`")]
+    MissingTargetExport {
+        /// The export name.
+        name: String,
+        /// The target world.
+        world: String,
+        /// The span where the error occurred.
+        #[label(primary, "must export `{name}` to target this world")]
+        span: SourceSpan,
+    },
+    /// An import or export has a mismatched type for the target world.
+    #[error("{kind} `{name}` has a mismatched type for target world `{world}`")]
+    TargetMismatch {
+        /// The kind of mismatch.
+        kind: ExternKind,
+        /// The mismatched extern name.
+        name: String,
+        /// The target world.
+        world: String,
+        /// The span where the error occurred.
+        #[label(primary, "mismatched type for {kind} `{name}`")]
+        span: SourceSpan,
+        /// The source of the error.
+        #[source]
+        source: anyhow::Error,
+    },
 }
 
 /// Represents a resolution result.
@@ -732,6 +770,17 @@ impl ItemKind {
             ItemKind::Value(_) => "value",
         }
     }
+
+    /// Promote function types, instance types, and component types
+    /// to functions, instances, and components
+    fn promote(&self) -> Self {
+        match *self {
+            ItemKind::Type(Type::Func(id)) => ItemKind::Func(id),
+            ItemKind::Type(Type::Interface(id)) => ItemKind::Instance(id),
+            ItemKind::Type(Type::World(id)) => ItemKind::Component(id),
+            kind => kind,
+        }
+    }
 }
 
 /// Represents a item defining a type.

crates/wac-parser/src/resolution/ast.rs

@@ -181,11 +181,29 @@ impl<'a> AstResolver<'a> {
             }
         }
 
+        // If there's a target world in the directive, validate the composition
+        // conforms to the target
+        if let Some(path) = &self.document.directive.targets {
+            let item = self.resolve_package_export(&mut state, path)?;
+            match item {
+                ItemKind::Type(Type::World(world)) => {
+                    self.validate_target(&state, path, world)?;
+                }
+                _ => {
+                    return Err(Error::NotWorld {
+                        name: path.string.to_owned(),
+                        kind: item.as_str(&self.definitions).to_owned(),
+                        span: path.span,
+                    });
+                }
+            }
+        }
+
         assert!(state.scopes.is_empty());
 
         Ok(Composition {
-            package: self.document.package.name.to_owned(),
-            version: self.document.package.version.clone(),
+            package: self.document.directive.package.name.to_owned(),
+            version: self.document.directive.package.version.clone(),
             definitions: self.definitions,
             packages: state.packages,
             items: state.current.items,
@@ -227,13 +245,8 @@ impl<'a> AstResolver<'a> {
             ast::ImportType::Ident(id) => (state.local_item(id)?.1.kind(), stmt.id.span),
         };
 
-        // Promote function types, instance types, and component types to functions, instances, and components
-        let kind = match kind {
-            ItemKind::Type(Type::Func(id)) => ItemKind::Func(id),
-            ItemKind::Type(Type::Interface(id)) => ItemKind::Instance(id),
-            ItemKind::Type(Type::World(id)) => ItemKind::Component(id),
-            _ => kind,
-        };
+        // Promote any types to their corresponding item kind
+        let kind = kind.promote();
 
         let (name, span) = if let Some(name) = &stmt.name {
             // Override the span to the `as` clause string
@@ -505,8 +518,8 @@ impl<'a> AstResolver<'a> {
     fn id(&self, name: &str) -> String {
         format!(
             "{pkg}/{name}{version}",
-            pkg = self.document.package.name,
-            version = if let Some(version) = &self.document.package.version {
+            pkg = self.document.directive.package.name,
+            version = if let Some(version) = &self.document.directive.package.version {
                 format!("@{version}")
             } else {
                 String::new()
@@ -1551,7 +1564,7 @@ impl<'a> AstResolver<'a> {
         path: &'a ast::PackagePath<'a>,
     ) -> ResolutionResult<ItemKind> {
         // Check for reference to local item
-        if path.name == self.document.package.name {
+        if path.name == self.document.directive.package.name {
             return self.resolve_local_export(state, path);
         }
 
@@ -1704,7 +1717,7 @@ impl<'a> AstResolver<'a> {
         state: &mut State<'a>,
         expr: &'a ast::NewExpr<'a>,
     ) -> ResolutionResult<ItemId> {
-        if expr.package.name == self.document.package.name {
+        if expr.package.name == self.document.directive.package.name {
             return Err(Error::UnknownPackage {
                 name: expr.package.name.to_string(),
                 span: expr.package.span,
@@ -2248,4 +2261,67 @@ impl<'a> AstResolver<'a> {
         aliases.insert(name.to_owned(), id);
         Ok(Some(id))
     }
+
+    fn validate_target(
+        &self,
+        state: &State,
+        path: &ast::PackagePath,
+        world: WorldId,
+    ) -> ResolutionResult<()> {
+        let world = &self.definitions.worlds[world];
+
+        let mut checker = SubtypeChecker::new(&self.definitions, &state.packages);
+
+        // The output is allowed to import a subset of the world's imports
+        for (name, import) in &state.imports {
+            let expected = world
+                .imports
+                .get(name)
+                .ok_or_else(|| Error::ImportNotInTarget {
+                    name: name.clone(),
+                    world: path.string.to_owned(),
+                    span: import.span,
+                })?;
+
+            checker
+                .is_subtype(
+                    expected.promote(),
+                    state.root_scope().items[import.item].kind(),
+                )
+                .map_err(|e| Error::TargetMismatch {
+                    kind: ExternKind::Import,
+                    name: name.clone(),
+                    world: path.string.to_owned(),
+                    span: import.span,
+                    source: e,
+                })?;
+        }
+
+        // The output must export every export in the world
+        for (name, expected) in &world.exports {
+            let export = state
+                .exports
+                .get(name)
+                .ok_or_else(|| Error::MissingTargetExport {
+                    name: name.clone(),
+                    world: path.string.to_owned(),
+                    span: path.span,
+                })?;
+
+            checker
+                .is_subtype(
+                    expected.promote(),
+                    state.root_scope().items[export.item].kind(),
+                )
+                .map_err(|e| Error::TargetMismatch {
+                    kind: ExternKind::Export,
+                    name: name.clone(),
+                    world: path.string.to_owned(),
+                    span: export.span,
+                    source: e,
+                })?;
+        }
+
+        Ok(())
+    }
 }

crates/wac-parser/tests/parser/export.wac.result

@@ -1,12 +1,14 @@
 {
   "docs": [],
-  "package": {
-    "string": "test:comp",
-    "name": "test:comp",
-    "version": null,
-    "span": {
-      "offset": 8,
-      "length": 9
+  "directive": {
+    "package": {
+      "string": "test:comp",
+      "name": "test:comp",
+      "version": null,
+      "span": {
+        "offset": 8,
+        "length": 9
+      }
     }
   },
   "statements": [