From 3eeb54861d310a37518e81642bee77120c097e00 Mon Sep 17 00:00:00 2001
From: Andy <anhans@microsoft.com>
Date: Tue, 10 Oct 2017 10:53:43 -0700
Subject: [PATCH] Fix invalid cast (#18821)

---
 src/compiler/binder.ts | 39 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index 48cace44841..4cacb5765db 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -2271,16 +2271,13 @@ namespace ts {
         function isExportsOrModuleExportsOrAlias(node: Node): boolean {
             return isExportsIdentifier(node) ||
                 isModuleExportsPropertyAccessExpression(node) ||
-                isNameOfExportsOrModuleExportsAliasDeclaration(node);
+                isIdentifier(node) && isNameOfExportsOrModuleExportsAliasDeclaration(node);
         }
 
-        function isNameOfExportsOrModuleExportsAliasDeclaration(node: Node) {
-            if (isIdentifier(node)) {
-                const symbol = lookupSymbolForName(node.escapedText);
-                return symbol && symbol.valueDeclaration && isVariableDeclaration(symbol.valueDeclaration) &&
-                    symbol.valueDeclaration.initializer && isExportsOrModuleExportsOrAliasOrAssignment(symbol.valueDeclaration.initializer);
-            }
-            return false;
+        function isNameOfExportsOrModuleExportsAliasDeclaration(node: Identifier): boolean {
+            const symbol = lookupSymbolForName(node.escapedText);
+            return symbol && symbol.valueDeclaration && isVariableDeclaration(symbol.valueDeclaration) &&
+                symbol.valueDeclaration.initializer && isExportsOrModuleExportsOrAliasOrAssignment(symbol.valueDeclaration.initializer);
         }
 
         function isExportsOrModuleExportsOrAliasOrAssignment(node: Node): boolean {
@@ -2354,20 +2351,22 @@ namespace ts {
             // Look up the function in the local scope, since prototype assignments should
             // follow the function declaration
             const leftSideOfAssignment = node.left as PropertyAccessExpression;
-            const target = leftSideOfAssignment.expression as Identifier;
+            const target = leftSideOfAssignment.expression;
 
-            // Fix up parent pointers since we're going to use these nodes before we bind into them
-            leftSideOfAssignment.parent = node;
-            target.parent = leftSideOfAssignment;
+            if (isIdentifier(target)) {
+                // Fix up parent pointers since we're going to use these nodes before we bind into them
+                leftSideOfAssignment.parent = node;
+                target.parent = leftSideOfAssignment;
 
-            if (isNameOfExportsOrModuleExportsAliasDeclaration(target)) {
-                // This can be an alias for the 'exports' or 'module.exports' names, e.g.
-                //    var util = module.exports;
-                //    util.property = function ...
-                bindExportsPropertyAssignment(node);
-            }
-            else {
-                bindPropertyAssignment(target.escapedText, leftSideOfAssignment, /*isPrototypeProperty*/ false);
+                if (isNameOfExportsOrModuleExportsAliasDeclaration(target)) {
+                    // This can be an alias for the 'exports' or 'module.exports' names, e.g.
+                    //    var util = module.exports;
+                    //    util.property = function ...
+                    bindExportsPropertyAssignment(node);
+                }
+                else {
+                    bindPropertyAssignment(target.escapedText, leftSideOfAssignment, /*isPrototypeProperty*/ false);
+                }
             }
         }