From e83dd931da7a1bb7828bd3326a6c561e50ecfd9b Mon Sep 17 00:00:00 2001
From: Hans Larsen <hans@hansl.ca>
Date: Thu, 12 Oct 2017 08:09:19 -0700
Subject: [PATCH] fix(@ngtools/webpack): fix for TypeScript module resolution
 cache missing in old version

---
 packages/@ngtools/webpack/src/plugin.ts | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/packages/@ngtools/webpack/src/plugin.ts b/packages/@ngtools/webpack/src/plugin.ts
index 25525b96dc0d..39bf7b4cdeeb 100644
--- a/packages/@ngtools/webpack/src/plugin.ts
+++ b/packages/@ngtools/webpack/src/plugin.ts
@@ -50,7 +50,7 @@ export class AotPlugin implements Tapable {
   private _compilerOptions: ts.CompilerOptions;
   private _angularCompilerOptions: any;
   private _program: ts.Program;
-  private _moduleResolutionCache: ts.ModuleResolutionCache;
+  private _moduleResolutionCache?: ts.ModuleResolutionCache;
   private _rootFilePath: string[];
   private _compilerHost: WebpackCompilerHost;
   private _resourceLoader: WebpackResourceLoader;
@@ -225,9 +225,11 @@ export class AotPlugin implements Tapable {
     this._program = ts.createProgram(
       this._rootFilePath, this._compilerOptions, this._compilerHost);
 
-    // We use absolute paths everywhere.
-    this._moduleResolutionCache = ts.createModuleResolutionCache(
-      this._basePath, (fileName: string) => fileName);
+    if (ts.createModuleResolutionCache) {
+      // We use absolute paths everywhere.
+      this._moduleResolutionCache = ts.createModuleResolutionCache(
+          this._basePath, (fileName: string) => fileName);
+    }
 
     // We enable caching of the filesystem in compilerHost _after_ the program has been created,
     // because we don't want SourceFile instances to be cached past this point.