readFile may return undefined

src/services/jsTyping.ts

@@ -9,10 +9,10 @@
 namespace ts.JsTyping {
 
     export interface TypingResolutionHost {
-        directoryExists: (path: string) => boolean;
-        fileExists: (fileName: string) => boolean;
-        readFile: (path: string, encoding?: string) => string;
-        readDirectory: (rootDir: string, extensions: ReadonlyArray<string>, excludes: ReadonlyArray<string>, includes: ReadonlyArray<string>, depth?: number) => string[];
+        directoryExists(path: string): boolean;
+        fileExists(fileName: string): boolean;
+        readFile(path: string, encoding?: string): string | undefined;
+        readDirectory(rootDir: string, extensions: ReadonlyArray<string>, excludes: ReadonlyArray<string>, includes: ReadonlyArray<string>, depth?: number): string[];
     }
 
     interface PackageJson {

src/services/services.ts

@@ -1149,7 +1149,7 @@ namespace ts {
                         !!hostCache.getEntryByPath(path) :
                         (host.fileExists && host.fileExists(fileName));
                 },
-                readFile: (fileName): string => {
+                readFile(fileName) {
                     // stub missing host functionality
                     const path = toPath(fileName, currentDirectory, getCanonicalFileName);
                     if (hostCache.containsEntryByPath(path)) {

src/services/shims.ts

@@ -69,7 +69,7 @@ namespace ts {
 
         getTypeRootsVersion?(): number;
         readDirectory(rootDir: string, extension: string, basePaths?: string, excludeEx?: string, includeFileEx?: string, includeDirEx?: string, depth?: number): string;
-        readFile(path: string, encoding?: string): string;
+        readFile(path: string, encoding?: string): string | undefined;
         fileExists(path: string): boolean;
 
         getModuleResolutionsForFile?(fileName: string): string;
@@ -95,7 +95,7 @@ namespace ts {
         /**
          * Read arbitary text files on disk, i.e. when resolution procedure needs the content of 'package.json' to determine location of bundled typings for node modules
          */
-        readFile(fileName: string): string;
+        readFile(fileName: string): string | undefined;
         realpath?(path: string): string;
         trace(s: string): void;
         useCaseSensitiveFileNames?(): boolean;
@@ -458,7 +458,7 @@ namespace ts {
             ));
         }
 
-        public readFile(path: string, encoding?: string): string {
+        public readFile(path: string, encoding?: string): string | undefined {
             return this.shimHost.readFile(path, encoding);
         }
 
@@ -501,7 +501,7 @@ namespace ts {
             return this.shimHost.fileExists(fileName);
         }
 
-        public readFile(fileName: string): string {
+        public readFile(fileName: string): string | undefined {
             return this.shimHost.readFile(fileName);
         }
 
@@ -1006,7 +1006,7 @@ namespace ts {
     class CoreServicesShimObject extends ShimBase implements CoreServicesShim {
         private logPerformance = false;
 
-        constructor(factory: ShimFactory, public logger: Logger, private host: CoreServicesShimHostAdapter) {
+        constructor(factory: ShimFactory, public readonly logger: Logger, private readonly host: CoreServicesShimHostAdapter) {
             super(factory);
         }
 

src/services/types.ts

@@ -165,7 +165,7 @@ namespace ts {
          * Without these methods, only completions for ambient modules will be provided.
          */
         readDirectory?(path: string, extensions?: ReadonlyArray<string>, exclude?: ReadonlyArray<string>, include?: ReadonlyArray<string>, depth?: number): string[];
-        readFile?(path: string, encoding?: string): string;
+        readFile?(path: string, encoding?: string): string | undefined;
         fileExists?(path: string): boolean;
 
         /*