Normative: Define default constructors using spec steps

spec.html

@@ -8357,10 +8357,11 @@ <h1>%ThrowTypeError% ( )</h1>
       <h1>MakeConstructor ( _F_ [ , _writablePrototype_ [ , _prototype_ ] ] )</h1>
       <p>The abstract operation MakeConstructor takes argument _F_ (a function object) and optional arguments _writablePrototype_ (a Boolean) and _prototype_ (an Object). It converts _F_ into a constructor. It performs the following steps when called:</p>
       <emu-alg>
-        1. Assert: _F_ is an ECMAScript function object.
-        1. Assert: IsConstructor(_F_) is *false*.
-        1. Assert: _F_ is an extensible object that does not have a *"prototype"* own property.
-        1. Set _F_.[[Construct]] to the definition specified in <emu-xref href="#sec-ecmascript-function-objects-construct-argumentslist-newtarget"></emu-xref>.
+        1. Assert: _F_ is an ECMAScript function object or a built-in function object.
+        1. If _F_ is an ECMAScript function object, then
+          1. Assert: IsConstructor(_F_) is *false*.
+          1. Assert: _F_ is an extensible object that does not have a *"prototype"* own property.
+          1. Set _F_.[[Construct]] to the definition specified in <emu-xref href="#sec-ecmascript-function-objects-construct-argumentslist-newtarget"></emu-xref>.
         1. Set _F_.[[ConstructorKind]] to ~base~.
         1. If _writablePrototype_ is not present, set _writablePrototype_ to *true*.
         1. If _prototype_ is not present, then
@@ -21150,22 +21151,19 @@ <h1>Runtime Semantics: ClassDefinitionEvaluation</h1>
         1. Let _proto_ be ! OrdinaryObjectCreate(_protoParent_).
         1. If |ClassBody_opt| is not present, let _constructor_ be ~empty~.
         1. Else, let _constructor_ be ConstructorMethod of |ClassBody|.
-        1. If _constructor_ is ~empty~, then
-          1. If |ClassHeritage_opt| is present, then
-            1. Set _constructor_ to the result of parsing the source text
-              <pre><code class="javascript">constructor(...args) { super(...args); }</code></pre>
-              using the syntactic grammar with the goal symbol |MethodDefinition[~Yield, ~Await]|.
-          1. Else,
-            1. Set _constructor_ to the result of parsing the source text
-              <pre><code class="javascript">constructor() {}</code></pre>
-              using the syntactic grammar with the goal symbol |MethodDefinition[~Yield, ~Await]|.
         1. Set the running execution context's LexicalEnvironment to _classScope_.
-        1. Let _constructorInfo_ be ! DefineMethod of _constructor_ with arguments _proto_ and _constructorParent_.
-        1. Let _F_ be _constructorInfo_.[[Closure]].
+        1. If _constructor_ is ~empty~, then
+          1. Let _steps_ be the algorithm steps defined in <emu-xref href="#sec-default-constructor-functions"></emu-xref>.
+          1. Let _F_ be ! CreateBuiltinFunction(_steps_, &laquo; [[ConstructorKind]], [[HomeObject]], [[SourceText]] &raquo;, ~empty~, _constructorParent_, *true*).
+          1. Perform ! SetFunctionLength(_F_, *+0*<sub>𝔽</sub>).
+          1. Set _F_.[[HomeObject]] to _proto_.
+        1. Else,
+          1. Let _constructorInfo_ be ! DefineMethod of _constructor_ with arguments _proto_ and _constructorParent_.
+          1. Let _F_ be _constructorInfo_.[[Closure]].
+          1. Perform MakeClassConstructor(_F_).
         1. Perform SetFunctionName(_F_, _className_).
         1. Perform MakeConstructor(_F_, *false*, _proto_).
         1. If |ClassHeritage_opt| is present, set _F_.[[ConstructorKind]] to ~derived~.
-        1. Perform MakeClassConstructor(_F_).
         1. Perform CreateMethodProperty(_proto_, *"constructor"*, _F_).
         1. If |ClassBody_opt| is not present, let _methods_ be a new empty List.
         1. Else, let _methods_ be NonConstructorMethodDefinitions of |ClassBody|.
@@ -21182,6 +21180,23 @@ <h1>Runtime Semantics: ClassDefinitionEvaluation</h1>
           1. Perform _classScope_.InitializeBinding(_classBinding_, _F_).
         1. Return _F_.
       </emu-alg>
+
+      <emu-clause id="sec-default-constructor-functions">
+        <h1>Default Constructor Functions</h1>
+        <p>When a Default Constructor Function is called with zero or more arguments which form the rest parameter ..._args_, the following steps are taken:</p>
+        <emu-alg>
+          1. If NewTarget is *undefined*, throw a *TypeError* exception.
+          1. Let _F_ be the active function object.
+          1. If _F_.[[ConstructorKind]] is ~derived~, then
+            1. NOTE: This branch behaves similarly to `constructor(...args) { super(...args); }`. The most notable distinction is that while the aforementioned ECMAScript source text observably calls `%Array.prototype[@@iterator]%`, this abstract operation does not.
+            1. Let _func_ be ? _F_.[[GetPrototypeOf]]().
+            1. If IsConstructor(_func_) is *false*, throw a *TypeError* exception.
+            1. Return ? Construct(_func_, _args_, NewTarget).
+          1. Else,
+            1. NOTE: This branch behaves similarly to `constructor() {}`.
+            1. Return ? OrdinaryCreateFromConstructor(NewTarget, `"%Object.prototype%"`).
+        </emu-alg>
+      </emu-clause>
     </emu-clause>
 
     <emu-clause id="sec-runtime-semantics-bindingclassdeclarationevaluation">
@@ -26279,7 +26294,10 @@ <h1>Function.prototype.toString ( )</h1>
         <p>When the `toString` method is called, the following steps are taken:</p>
         <emu-alg>
           1. Let _func_ be the *this* value.
-          1. If _func_ is a <emu-xref href="#sec-built-in-function-objects">built-in function object</emu-xref>, return an implementation-defined String source code representation of _func_. The representation must have the syntax of a |NativeFunction|. Additionally, if _func_ has an [[InitialName]] internal slot and _func_.[[InitialName]] is a String, the portion of the returned String that would be matched by |NativeFunctionAccessor?| |PropertyName| must be the value of _func_.[[InitialName]].
+          1. If _func_ is a <emu-xref href="#sec-built-in-function-objects">built-in function object</emu-xref>, then
+            1. If _func_ has a [[SourceText]] internal slot and _func_.[[SourceText]] is a sequence of Unicode code points, then
+              1. Return ! CodePointsToString(_func_.[[SourceText]]).
+            1. Return an implementation-defined String source code representation of _func_. The representation must have the syntax of a |NativeFunction|. Additionally, if _func_ has an [[InitialName]] internal slot and _func_.[[InitialName]] is a String, the portion of the returned String that would be matched by |NativeFunctionAccessor?| |PropertyName| must be the value of _func_.[[InitialName]].
           1. If Type(_func_) is Object and _func_ has a [[SourceText]] internal slot and _func_.[[SourceText]] is a sequence of Unicode code points and ! HostHasSourceTextAvailable(_func_) is *true*, then
             1. Return ! CodePointsToString(_func_.[[SourceText]]).
           1. If Type(_func_) is Object and IsCallable(_func_) is *true*, return an implementation-defined String source code representation of _func_. The representation must have the syntax of a |NativeFunction|.