allow test harness to provide a mock fileExists function

Author: basarat

src/harness/harnessLanguageService.ts

@@ -190,6 +190,7 @@ module Harness.LanguageService {
         log(s: string): void { }
         trace(s: string): void { }
         error(s: string): void { }
+        fileExists = (fn: string) => this.getFilenames().some(serviceAdaptorFileName=> serviceAdaptorFileName === fn);
     }
 
     export class NativeLanugageServiceAdapter implements LanguageServiceAdapter {
@@ -236,6 +237,7 @@ module Harness.LanguageService {
         log(s: string): void { this.nativeHost.log(s); }
         trace(s: string): void { this.nativeHost.trace(s); }
         error(s: string): void { this.nativeHost.error(s); }
+        fileExists(fn: string) { return this.nativeHost.fileExists(fn); }
     }
 
     class ClassifierShimProxy implements ts.Classifier { 

src/services/services.ts

@@ -960,6 +960,9 @@ module ts {
         log? (s: string): void;
         trace? (s: string): void;
         error? (s: string): void;
+        
+        // Needed for mocking support
+        fileExists? (s: string): boolean;
     }
 
     //
@@ -2436,7 +2439,7 @@ module ts {
                 getDefaultLibFileName: (options) => host.getDefaultLibFileName(options),
                 writeFile: (fileName, data, writeByteOrderMark) => { },
                 readFile: (fileName) => sys.readFile(fileName),
-                fileExists: (fileName) => !!hostCache.getOrCreateEntry(fileName),
+                fileExists: host.fileExists ? (fn) => host.fileExists(fn) : sys.fileExists,
                 getCurrentDirectory: () => host.getCurrentDirectory(),
             });
 

src/services/shims.ts

@@ -56,6 +56,7 @@ module ts {
         getDefaultLibFileName(options: string): string;
         getNewLine?(): string;
         getProjectVersion?(): string;
+        fileExists(fileName: string): boolean;
     }
 
     /** Public interface of the the of a config service shim instance.*/
@@ -260,6 +261,10 @@ module ts {
         public error(s: string): void {
             this.shimHost.error(s);
         }
+        
+        public fileExists(fn: string): boolean {
+            return this.shimHost.fileExists(fn);
+        }
 
         public getProjectVersion(): string {
             if (!this.shimHost.getProjectVersion) {