feat: Add support for Node’s [util.inspect.custom] symbol method

lib/constructs/interface.js

@@ -1373,6 +1373,26 @@ class Interface {
       const props = [...classProps].map(([name, body]) => `${name}: ${body}`);
       this.str += `Object.defineProperties(${this.name}, { ${props.join(", ")} });`;
     }
+
+    // This code can't currently be generated as the operation, parameters
+    // and overloads code doesn't currently support symbol properties.
+    // This method is also made non-enumerable to match the other 'utils' symbol properties.
+    this.str += `
+
+        if (utils.hasOwn(Impl.implementation.prototype, utils.inspectCustomSymbol)) {
+          Object.defineProperty(${this.name}.prototype, utils.inspectCustomSymbol, {
+            value(depth, ctx) {
+              if (!exports.is(this)) {
+                throw new TypeError("Illegal invocation");
+              }
+              return this[impl][utils.inspectCustomSymbol](...arguments);
+            },
+            writable: true,
+            enumerable: false,
+            configurable: true
+          });
+        }
+    `;
   }
 
   generateOnInstance() {

lib/output/utils.js

@@ -11,6 +11,7 @@ const wrapperSymbol = Symbol("wrapper");
 const implSymbol = Symbol("impl");
 const sameObjectCaches = Symbol("SameObject caches");
 const ctorRegistrySymbol = Symbol.for("[webidl2js]  constructor registry");
+const inspectCustomSymbol = Symbol.for("nodejs.util.inspect.custom");
 
 function getSameObject(wrapper, prop, creator) {
   if (!wrapper[sameObjectCaches]) {
@@ -91,6 +92,7 @@ module.exports = exports = {
   implSymbol,
   getSameObject,
   ctorRegistrySymbol,
+  inspectCustomSymbol,
   wrapperForImpl,
   implForWrapper,
   tryWrapperForImpl,