Add and use utils.define(…) helper

Author: ExE-Boss

Diff for: lib/constructs/interface.js

@@ -1277,11 +1277,7 @@ class Interface {
 
     if (_needsUnforgeablesObject) {
       this.str += `
-        const unforgeables = getUnforgeables(globalObject);
-        for (const key of Reflect.ownKeys(unforgeables)) {
-          const descriptor = Reflect.getOwnPropertyDescriptor(unforgeables, key);
-          Object.defineProperty(wrapper, key, descriptor);
-        }
+        utils.define(wrapper, getUnforgeables(globalObject));
       `;
     }
 
@@ -1572,10 +1568,9 @@ class Interface {
     const propStrs = [...props].map(([name, body]) => `${name}: ${body}`);
     if (methods.length > 0) {
       this.str += `
-        Object.defineProperties(
-          wrapper,
-          Object.getOwnPropertyDescriptors({ ${methods.join(", ")} })
-        );
+        utils.define(wrapper, {
+          ${methods.join(", ")}
+        });
       `;
     }
     if (propStrs.length > 0) {
@@ -1626,16 +1621,13 @@ class Interface {
       function getUnforgeables(globalObject) {
         let unforgeables = unforgeablesMap.get(globalObject);
         if (unforgeables === undefined) {
-          unforgeables = Object.create(
-            null,
+          unforgeables = Object.create(null);
     `;
 
     if (methods.length > 0) {
-      this.str += `Object.getOwnPropertyDescriptors({ ${methods.join(", ")} }),`;
+      this.str += `utils.define(unforgeables, { ${methods.join(", ")} });`;
     }
 
-    this.str += ");";
-
     if (props.size > 0) {
       const propStrs = [...props].map(([name, body]) => `${name}: ${body}`);
       this.str += `

Diff for: lib/output/utils.js

@@ -7,6 +7,17 @@ function isObject(value) {
 
 const hasOwn = Function.prototype.call.bind(Object.prototype.hasOwnProperty);
 
+// Like `Object.assign`, but using `[[GetOwnProperty]]` and `[[DefineOwnProperty]]`
+// instead of `[[Get]]` and `[[Set]]` and only allowing objects
+function define(target, source) {
+  for (const key of Reflect.ownKeys(source)) {
+    const descriptor = Reflect.getOwnPropertyDescriptor(source, key);
+    if (descriptor && !Reflect.defineProperty(target, key, descriptor)) {
+      throw new TypeError(`Cannot redefine property: ${String(key)}`);
+    }
+  }
+}
+
 const wrapperSymbol = Symbol("wrapper");
 const implSymbol = Symbol("impl");
 const sameObjectCaches = Symbol("SameObject caches");
@@ -131,6 +142,7 @@ const asyncIteratorEOI = Symbol("async iterator end of iteration");
 module.exports = exports = {
   isObject,
   hasOwn,
+  define,
   wrapperSymbol,
   implSymbol,
   getSameObject,