Include 'delete' operator in control flow analysis

Author: ahejlsberg

src/compiler/binder.ts

@@ -580,6 +580,9 @@ namespace ts {
                 case SyntaxKind.BinaryExpression:
                     bindBinaryExpressionFlow(<BinaryExpression>node);
                     break;
+                case SyntaxKind.DeleteExpression:
+                    bindDeleteExpressionFlow(<DeleteExpression>node);
+                    break;
                 case SyntaxKind.ConditionalExpression:
                     bindConditionalExpressionFlow(<ConditionalExpression>node);
                     break;
@@ -1055,6 +1058,13 @@ namespace ts {
             }
         }
 
+        function bindDeleteExpressionFlow(node: DeleteExpression) {
+            forEachChild(node, bind);
+            if (node.expression.kind === SyntaxKind.PropertyAccessExpression) {
+                bindAssignmentTargetFlow(node.expression);
+            }
+        }
+
         function bindConditionalExpressionFlow(node: ConditionalExpression) {
             const trueLabel = createBranchLabel();
             const falseLabel = createBranchLabel();

src/compiler/checker.ts

@@ -7563,6 +7563,8 @@ namespace ts {
                     return checkRightHandSideOfForOf((<ForOfStatement>parent).expression) || unknownType;
                 case SyntaxKind.BinaryExpression:
                     return getAssignedTypeOfBinaryExpression(<BinaryExpression>parent);
+                case SyntaxKind.DeleteExpression:
+                    return undefinedType;
                 case SyntaxKind.ArrayLiteralExpression:
                     return getAssignedTypeOfArrayLiteralElement(<ArrayLiteralExpression>parent, node);
                 case SyntaxKind.SpreadElementExpression: