Implement support for the [Exposed] extended attribute (#192)

This also fixes a bug where `install` takes `globalName` instead of `globalNames`.

Author: ExE-Boss

README.md

@@ -264,10 +264,12 @@ Performs the Web IDL conversion algorithm for this interface, converting _value_
 
 In practice, this means doing a type-check equivalent to `is(value)`, and if it passes, returns the corresponding impl. If the type-check fails, it throws an informative exception. _context_ can be used to describe the provided value in any resulting error message.
 
-#### `install(globalObject)`
+#### `install(globalObject, globalNames)`
 
 This method creates a brand new wrapper constructor and prototype and attach it to the passed `globalObject`. It also registers the created constructor with the `globalObject`'s global constructor registry, which makes `create()`, `createImpl()`, and `setup()` work. (Thus, it is important to invoke `install()` before invoking those methods, as otherwise they will throw.)
 
+The second argument `globalNames` is an array containing the [global names](https://heycam.github.io/webidl/#dfn-global-name) of the interface that `globalObject` implements. This is used for the purposes of deciding which interfaces are [exposed](https://heycam.github.io/webidl/#dfn-exposed). For example, this array should be `["Window"]` for a [`Window`](https://html.spec.whatwg.org/multipage/window-object.html#window) global object. But for a [`DedicatedWorkerGlobalScope`](https://html.spec.whatwg.org/multipage/workers.html#dedicatedworkerglobalscope) global object, this array should be `["Worker", "DedicatedWorker"]`. Note that we do not yet implement [`[SecureContext]`](https://heycam.github.io/webidl/#SecureContext), so the "exposed" check is not fully implemented.
+
 #### `create(globalObject, constructorArgs, privateData)`
 
 Creates a new instance of the wrapper class and corresponding implementation class, passing in the `globalObject`, the `constructorArgs` array and `privateData` object to the implementation class constructor. Then returns the wrapper class.
@@ -454,6 +456,7 @@ webidl2js is implementing an ever-growing subset of the Web IDL specification. S
 - Variadic arguments
 - `[Clamp]`
 - `[EnforceRange]`
+- `[Exposed]`
 - `[LegacyArrayClass]`
 - `[LegacyUnenumerableNamedProperties]`
 - `[LegacyWindowAlias]`
@@ -478,7 +481,6 @@ Notable missing features include:
 - `[AllowShared]`
 - `[Default]` (for `toJSON()` operations)
 - `[Global]`'s various consequences, including the named properties object and `[[SetPrototypeOf]]`
-- `[Exposed]`
 - `[LenientSetter]`
 - `[LenientThis]`
 - `[NamedConstructor]`

lib/constructs/callback-interface.js

@@ -20,6 +20,25 @@ class CallbackInterface {
 
     this._analyzed = false;
     this._outputStaticProperties = new Map();
+
+    const exposed = utils.getExtAttr(this.idl.extAttrs, "Exposed");
+    if (this.idl.members.some(member => member.type === "const") && !exposed) {
+      throw new Error(`Callback interface ${this.name} with defined constants lacks the [Exposed] extended attribute`);
+    }
+
+    if (exposed) {
+      if (!exposed.rhs || (exposed.rhs.type !== "identifier" && exposed.rhs.type !== "identifier-list")) {
+        throw new Error(`[Exposed] must take an identifier or an identifier list in callback interface ${this.name}`);
+      }
+
+      if (exposed.rhs.type === "identifier") {
+        this.exposed = new Set([exposed.rhs.value]);
+      } else {
+        this.exposed = new Set(exposed.rhs.value.map(token => token.value));
+      }
+    } else {
+      this.exposed = new Set();
+    }
   }
 
   _analyzeMembers() {
@@ -178,14 +197,24 @@ class CallbackInterface {
   }
 
   generateInstall() {
+    if (this.constants.size > 0) {
+      this.str += `
+        const exposed = new Set(${JSON.stringify([...this.exposed])});
+      `;
+    }
+
     this.str += `
-      exports.install = function install(globalObject) {
+      exports.install = (globalObject, globalNames) => {
     `;
 
     if (this.constants.size > 0) {
       const { name } = this;
 
       this.str += `
+        if (!globalNames.some(globalName => exposed.has(globalName))) {
+          return;
+        }
+
         const ${name} = () => {
           throw new TypeError("Illegal invocation");
         };
@@ -234,4 +263,6 @@ class CallbackInterface {
   }
 }
 
+CallbackInterface.prototype.type = "callback interface";
+
 module.exports = CallbackInterface;

lib/constructs/interface.js

@@ -1463,7 +1463,12 @@ class Interface {
     const { idl, name } = this;
 
     this.str += `
-      exports.install = (globalObject, globalName) => {
+      const exposed = new Set(${JSON.stringify([...this.exposed])});
+
+      exports.install = (globalObject, globalNames) => {
+        if (!globalNames.some(globalName => exposed.has(globalName))) {
+          return;
+        }
     `;
 
     if (idl.inheritance) {
@@ -1500,7 +1505,7 @@ class Interface {
 
       if (this.legacyWindowAliases) {
         this.str += `
-          if (globalName === "Window") {
+          if (globalNames.includes("Window")) {
         `;
 
         for (const legacyWindowAlias of this.legacyWindowAliases) {