Implement [LegacyLenientSetter] and fix [LegacyLenientThis]

README.md

@@ -470,6 +470,7 @@ webidl2js is implementing an ever-growing subset of the Web IDL specification. S
 - `[EnforceRange]`
 - `[Exposed]`
 - `[LegacyLenientThis]`
+- `[LegacyLenientSetter]`
 - `[LegacyNoInterfaceObject]`
 - `[LegacyNullToEmptyString]`
 - `[LegacyOverrideBuiltins]`
@@ -494,7 +495,6 @@ Notable missing features include:
 - `[Default]` (for `toJSON()` operations)
 - `[Global]`'s various consequences, including the named properties object and `[[SetPrototypeOf]]`
 - `[LegacyFactoryFunction]`
-- `[LegacyLenientSetter]`
 - `[LegacyNamespace]`
 - `[LegacyTreatNonObjectAsNull]`
 - `[SecureContext]`

lib/constructs/attribute.js

@@ -48,8 +48,16 @@ class Attribute {
       setterBody = processedOutput.set;
     }
 
-    if (utils.getExtAttr(this.idl.extAttrs, "LegacyLenientThis")) {
-      brandCheck = "";
+    const replaceable = utils.getExtAttr(this.idl.extAttrs, "Replaceable");
+    const legacyLenientSetter = utils.getExtAttr(this.idl.extAttrs, "LegacyLenientSetter");
+    const legacyLenientThis = utils.getExtAttr(this.idl.extAttrs, "LegacyLenientThis");
+
+    if (legacyLenientThis) {
+      brandCheck = `
+        if (!exports.is(esValue)) {
+          return;
+        }
+      `;
     }
 
     if (sameObject) {
@@ -94,23 +102,47 @@ class Attribute {
         ${idlConversion}
         ${setterBody}
       `, "set", { configurable });
-    } else if (utils.getExtAttr(this.idl.extAttrs, "PutForwards")) {
-      addMethod(this.idl.name, ["V"], `
-        const esValue = this !== null && this !== undefined ? this : globalObject;
-        ${brandCheck}
-        this.${this.idl.name}.${utils.getExtAttr(this.idl.extAttrs, "PutForwards").rhs.value} = V;
-      `, "set", { configurable });
-    } else if (utils.getExtAttr(this.idl.extAttrs, "Replaceable")) {
-      addMethod(this.idl.name, ["V"], `
-        const esValue = this !== null && this !== undefined ? this : globalObject;
-        ${brandCheck}
-        Object.defineProperty(esValue, "${this.idl.name}", {
-          configurable: true,
-          enumerable: true,
-          value: V,
-          writable: true
-        });
-      `, "set", { configurable });
+    } else {
+      const putForwards = utils.getExtAttr(this.idl.extAttrs, "PutForwards");
+
+      setterBody = "";
+      if (replaceable) {
+        if (legacyLenientThis) {
+          brandCheck = "";
+        }
+
+        setterBody = `
+          Object.defineProperty(esValue, "${this.idl.name}", {
+            configurable: true,
+            enumerable: true,
+            value: V,
+            writable: true
+          });
+        `;
+      } else if (putForwards) {
+        setterBody = `
+          const Q = esValue["${this.idl.name}"];
+          if (!utils.isObject(Q)) {
+            throw new TypeError("Property '${this.idl.name}' is not an object");
+          }
+        `;
+
+        // WebIDL calls the `Set` abstract operation with a `Throw` value of `false`:
+        setterBody += `Reflect.set(Q, "${putForwards.rhs.value}", V);`;
+      }
+
+      if (setterBody) {
+        addMethod(this.idl.name, ["V"], `
+          const esValue = this !== null && this !== undefined ? this : globalObject;
+          ${brandCheck}
+          ${setterBody}
+        `, "set", { configurable });
+      } else if (legacyLenientSetter) {
+        addMethod(this.idl.name, ["V"], legacyLenientThis ? "" : `
+          const esValue = this !== null && this !== undefined ? this : globalObject;
+          ${brandCheck}
+        `, "set", { configurable });
+      }
     }
 
     if (!this.static && this.idl.special === "stringifier") {