Normative: close underlying iterators when return is called before ne…

…xt (#267)

Co-authored-by: Michael Ficarra <m.ficarra@f5.com>

spec.html

@@ -271,8 +271,16 @@ <h1>%IteratorHelperPrototype%.next ( )</h1>
         <emu-clause id="sec-%iteratorhelperprototype%.return">
           <h1>%IteratorHelperPrototype%.return ( )</h1>
           <emu-alg>
+            1. Let _O_ be *this* value.
+            1. Perform ? RequireInternalSlot(_O_, [[UnderlyingIterator]]).
+            1. Assert: _O_ has a [[GeneratorState]] slot.
+            1. If _O_.[[GeneratorState]] is ~suspendedStart~, then
+              1. Set _O_.[[GeneratorState]] to ~completed~.
+              1. NOTE: Once a generator enters the completed state it never leaves it and its associated execution context is never resumed. Any execution state associated with _O_ can be discarded at this point.
+              1. Perform ? IteratorClose(_O_.[[UnderlyingIterator]], NormalCompletion(~unused~)).
+              1. Return CreateIterResultObject(*undefined*, *true*).
             1. Let _C_ be Completion { [[Type]]: ~return~, [[Value]]: *undefined*, [[Target]]: ~empty~ }.
-            1. Return ? GeneratorResumeAbrupt(*this* value, _C_, *"Iterator Helper"*).
+            1. Return ? GeneratorResumeAbrupt(_O_, _C_, *"Iterator Helper"*).
           </emu-alg>
         </emu-clause>
 
@@ -317,7 +325,9 @@ <h1>Iterator.prototype.map ( _mapper_ )</h1>
               1. Let _completion_ be Completion(Yield(_mapped_)).
               1. IfAbruptCloseIterator(_completion_, _iterated_).
               1. Set _counter_ to _counter_ + 1.
-          1. Return CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%).
+          1. Let _result_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterator]] »).
+          1. Set _result_.[[UnderlyingIterator]] to _iterated_.
+          1. Return _result_.
         </emu-alg>
       </emu-clause>
 
@@ -341,7 +351,9 @@ <h1>Iterator.prototype.filter ( _predicate_ )</h1>
                 1. Let _completion_ be Completion(Yield(_value_)).
                 1. IfAbruptCloseIterator(_completion_, _iterated_).
               1. Set _counter_ to _counter_ + 1.
-          1. Return CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%).
+          1. Let _result_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterator]] »).
+          1. Set _result_.[[UnderlyingIterator]] to _iterated_.
+          1. Return _result_.
         </emu-alg>
       </emu-clause>
 
@@ -367,7 +379,9 @@ <h1>Iterator.prototype.take ( _limit_ )</h1>
               1. If _next_ is *false*, return *undefined*.
               1. Let _completion_ be Completion(Yield(? IteratorValue(_next_))).
               1. IfAbruptCloseIterator(_completion_, _iterated_).
-          1. Return CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%).
+          1. Let _result_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterator]] »).
+          1. Set _result_.[[UnderlyingIterator]] to _iterated_.
+          1. Return _result_.
         </emu-alg>
       </emu-clause>
 
@@ -394,7 +408,9 @@ <h1>Iterator.prototype.drop ( _limit_ )</h1>
               1. If _next_ is *false*, return *undefined*.
               1. Let _completion_ be Completion(Yield(? IteratorValue(_next_))).
               1. IfAbruptCloseIterator(_completion_, _iterated_).
-          1. Return CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%).
+          1. Let _result_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterator]] »).
+          1. Set _result_.[[UnderlyingIterator]] to _iterated_.
+          1. Return _result_.
         </emu-alg>
       </emu-clause>
 
@@ -431,7 +447,9 @@ <h1>Iterator.prototype.flatMap ( _mapper_ )</h1>
                     1. IfAbruptCloseIterator(_backupCompletion_, _iterated_).
                     1. Return ? IteratorClose(_completion_, _iterated_).
               1. Set _counter_ to _counter_ + 1.
-          1. Return CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%).
+          1. Let _result_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterator]] »).
+          1. Set _result_.[[UnderlyingIterator]] to _iterated_.
+          1. Return _result_.
         </emu-alg>
       </emu-clause>
 
@@ -567,3 +585,38 @@ <h1>Iterator.prototype [ @@toStringTag ]</h1>
     </emu-clause>
   </emu-clause>
 </emu-clause>
+
+<emu-clause id="updated-abstract-operations">
+  <h1>Updated Abstract Operations</h1>
+
+  <emu-clause id="sec-createiteratorfromclosure" type="abstract operation">
+    <h1>
+      CreateIteratorFromClosure (
+        _closure_: an Abstract Closure with no parameters,
+        _generatorBrand_: a String or ~empty~,
+        _generatorPrototype_: an Object,
+        <ins>optional _extraSlots_: a List of names of internal slots,</ins>
+      ): a Generator
+    </h1>
+    <dl class="header">
+    </dl>
+    <emu-alg>
+      1. NOTE: _closure_ can contain uses of the Yield operation to yield an IteratorResult object.
+      1. <ins>If _extraSlots_ is not present, set _extraSlots_ to a new empty List.</ins>
+      1. Let _internalSlotsList_ be <ins>the list-concatenation of _extraSlots_ and</ins> « [[GeneratorState]], [[GeneratorContext]], [[GeneratorBrand]] ».
+      1. Let _generator_ be OrdinaryObjectCreate(_generatorPrototype_, _internalSlotsList_).
+      1. Set _generator_.[[GeneratorBrand]] to _generatorBrand_.
+      1. Set _generator_.[[GeneratorState]] to *undefined*.
+      1. Let _callerContext_ be the running execution context.
+      1. Let _calleeContext_ be a new execution context.
+      1. Set the Function of _calleeContext_ to *null*.
+      1. Set the Realm of _calleeContext_ to the current Realm Record.
+      1. Set the ScriptOrModule of _calleeContext_ to _callerContext_'s ScriptOrModule.
+      1. If _callerContext_ is not already suspended, suspend _callerContext_.
+      1. Push _calleeContext_ onto the execution context stack; _calleeContext_ is now the running execution context.
+      1. Perform GeneratorStart(_generator_, _closure_).
+      1. Remove _calleeContext_ from the execution context stack and restore _callerContext_ as the running execution context.
+      1. Return _generator_.
+    </emu-alg>
+  </emu-clause>
+</emu-clause>