Bug 1147371: Implement IteratorClose for for-of

Issue #74

js/src/jsiter.cpp

@@ -12,6 +12,7 @@
 #include "mozilla/Maybe.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/PodOperations.h"
+#include "mozilla/Unused.h"
 
 #include "jsarray.h"
 #include "jsatom.h"
@@ -1229,6 +1230,7 @@ js::CloseIterator(JSContext* cx, HandleObject obj)
         }
         return LegacyGeneratorObject::close(cx, obj);
     }
+
     return true;
 }
 
@@ -1246,6 +1248,56 @@ js::UnwindIteratorForException(JSContext* cx, HandleObject obj)
     return true;
 }
 
+bool
+js::IteratorCloseForException(JSContext* cx, HandleObject obj)
+{
+    MOZ_ASSERT(cx->isExceptionPending());
+
+    bool isClosingGenerator = cx->isClosingGenerator();
+    JS::AutoSaveExceptionState savedExc(cx);
+
+    // Implements IteratorClose (ES 7.4.6) for exception unwinding. See
+    // also the bytecode generated by BytecodeEmitter::emitIteratorClose.
+
+    // Step 3.
+    //
+    // Get the "return" method.
+    RootedValue returnMethod(cx);
+    if (!GetProperty(cx, obj, obj, cx->names().return_, &returnMethod))
+        return false;
+
+    // Step 4.
+    //
+    // Do nothing if "return" is null or undefined. Throw a TypeError if the
+    // method is not IsCallable.
+    if (returnMethod.isNullOrUndefined())
+        return true;
+    if (!IsCallable(returnMethod))
+        return ReportIsNotFunction(cx, returnMethod);
+
+    // Step 5, 6, 8.
+    //
+    // Call "return" if it is not null or undefined.
+    RootedValue rval(cx);
+    bool ok = Call(cx, returnMethod, obj, &rval);
+    if (isClosingGenerator) {
+        // Closing an iterator is implemented as an exception, but in spec
+        // terms it is a Completion value with [[Type]] return. In this case
+        // we *do* care if the call threw and if it returned an object.
+        if (!ok)
+            return false;
+        if (!rval.isObject())
+            return ThrowCheckIsObject(cx, CheckIsObjectKind::IteratorReturn);
+    } else {
+        // We don't care if the call threw or that it returned an Object, as
+        // Step 6 says if IteratorClose is being called during a throw, the
+        // original throw has primacy.
+        savedExc.restore();
+    }
+
+    return true;
+}
+
 void
 js::UnwindIteratorForUncatchableException(JSContext* cx, JSObject* obj)
 {