Array Destructuring issue on .next function.

akroshg · akroshg · commit cb3f37fdafc9 · 2016-05-18T17:17:43.000-07:00
The iterator.next should not be called if the last slot is empty slot. Fixed that and added the test.
diff --git a/lib/Runtime/ByteCode/ByteCodeEmitter.cpp b/lib/Runtime/ByteCode/ByteCodeEmitter.cpp
@@ -6166,9 +6166,10 @@ void EmitDestructuredArray(
             elem = list;
         }
 
-        if (elem->nop == knopEllipsis)
+        if (elem->nop == knopEllipsis
+            || (elem->nop == knopEmpty && list->nop == knopEmpty))
         {
-            // Rest must be the last argument - no need to continue.
+            // Rest and last empty slot do not require any more processing.
             break;
         }
 
@@ -6190,6 +6191,7 @@ void EmitDestructuredArray(
             break;
         }
 
+
         byteCodeGenerator->StartStatement(elem);
 
         Js::RegSlot itemLocation = funcInfo->AcquireTmpRegister();
diff --git a/test/es6/destructuring.js b/test/es6/destructuring.js
@@ -581,6 +581,40 @@ var tests = [
         }
         assert.isTrue(foo(), "Array destructuring pattern on for..in is initialized correctly");
       }
+      
+      {
+         let obj1 = {};
+         obj1[Symbol.iterator] = function () {
+            return {
+                next: function() {
+                    assert.fail("next function should not be called");
+                }
+            };
+         };
+         
+         // Empty slot should not call next on the iterator.
+         var [] = obj1;
+      }
+
+      {
+         let obj1 = {};
+         obj1[Symbol.iterator] = function () {
+            return {
+                next: function() {
+                    this.counter++;
+                    if (this.counter > 1)
+                    {
+                        assert.fail("next function should not be called for the second time");
+                    }
+                    return {value : undefined, done: false};
+                },
+                counter : 0
+            };
+         };
+         
+         // Second empty slot should not call next on the iterator.
+         var [,] = obj1;
+      }
 
     }
   }

Original file line number	Diff line number	Diff line change
`@@ -6166,9 +6166,10 @@ void EmitDestructuredArray(`
`6166`	`6166`	`elem = list;`
`6167`	`6167`	`}`
`6168`	`6168`
`6169`		`- if (elem->nop == knopEllipsis)`
	`6169`	`+ if (elem->nop == knopEllipsis`
	`6170`	`+ \|\| (elem->nop == knopEmpty && list->nop == knopEmpty))`
`6170`	`6171`	`{`
`6171`		`- // Rest must be the last argument - no need to continue.`
	`6172`	`+ // Rest and last empty slot do not require any more processing.`
`6172`	`6173`	`break;`
`6173`	`6174`	`}`
`6174`	`6175`
`@@ -6190,6 +6191,7 @@ void EmitDestructuredArray(`
`6190`	`6191`	`break;`
`6191`	`6192`	`}`
`6192`	`6193`
	`6194`	`+`
`6193`	`6195`	`byteCodeGenerator->StartStatement(elem);`
`6194`	`6196`
`6195`	`6197`	`Js::RegSlot itemLocation = funcInfo->AcquireTmpRegister();`