factor out helpers + cleanup startsWith and friends

src/compiler/core.ts

@@ -1730,13 +1730,18 @@ namespace ts {
 
     /* @internal */
     export function startsWith(str: string, prefix: string): boolean {
-        return str.lastIndexOf(prefix, 0) === 0;
+        return str.indexOf(prefix) === 0;
+    }
+
+    /* @internal */
+    export function removePrefix(str: string, prefix: string | undefined): string {
+        return startsWith(str, prefix) ? str.substr(prefix.length) : str;
     }
 
     /* @internal */
     export function endsWith(str: string, suffix: string): boolean {
         const expectedPos = str.length - suffix.length;
-        return expectedPos >= 0 && str.indexOf(suffix, expectedPos) === expectedPos;
+        return expectedPos >= 0 && str.lastIndexOf(suffix, expectedPos) === expectedPos;
     }
 
     export function hasExtension(fileName: string): boolean {
@@ -1747,7 +1752,7 @@ namespace ts {
         return path.length > extension.length && endsWith(path, extension);
     }
 
-    export function fileExtensionIsAny(path: string, extensions: string[]): boolean {
+    export function fileExtensionIsOneOf(path: string, extensions: string[]): boolean {
         for (const extension of extensions) {
             if (fileExtensionIs(path, extension)) {
                 return true;
@@ -1947,7 +1952,7 @@ namespace ts {
             for (const current of files) {
                 const name = combinePaths(path, current);
                 const absoluteName = combinePaths(absolutePath, current);
-                if (extensions && !fileExtensionIsAny(name, extensions)) continue;
+                if (extensions && !fileExtensionIsOneOf(name, extensions)) continue;
                 if (excludeRegex && excludeRegex.test(absoluteName)) continue;
                 if (!includeFileRegexes) {
                     results[0].push(name);

src/compiler/moduleNameResolver.ts

@@ -958,10 +958,13 @@ namespace ts {
         }
     }
 
+    /** Double underscores are used in DefinitelyTyped to delimit scoped packages. */
+    const mangledScopedPackageSeparator = "__";
+
     /** For a scoped package, we must look in `@types/foo__bar` instead of `@types/@foo/bar`. */
     function mangleScopedPackage(moduleName: string, state: ModuleResolutionState): string {
         if (startsWith(moduleName, "@")) {
-            const replaceSlash = moduleName.replace(ts.directorySeparator, "__");
+            const replaceSlash = moduleName.replace(ts.directorySeparator, mangledScopedPackageSeparator);
             if (replaceSlash !== moduleName) {
                 const mangled = replaceSlash.slice(1); // Take off the "@"
                 if (state.traceEnabled) {
@@ -973,6 +976,16 @@ namespace ts {
         return moduleName;
     }
 
+    export function getPackageNameFromAtTypesDirectory(mangledName: string): string {
+        const withoutAtTypePrefix = removePrefix(mangledName, "@types/");
+        if (withoutAtTypePrefix !== mangledName) {
+            return withoutAtTypePrefix.indexOf("__") !== -1 ?
+                "@" + withoutAtTypePrefix.replace(mangledScopedPackageSeparator, ts.directorySeparator) :
+                withoutAtTypePrefix;
+        }
+        return mangledName;
+    }
+
     function tryFindNonRelativeModuleNameInCache(cache: PerModuleNameCache | undefined, moduleName: string, containingDirectory: string, traceEnabled: boolean, host: ModuleResolutionHost): SearchResult<Resolved> {
         const result = cache && cache.get(containingDirectory);
         if (result) {

src/services/codefixes/importFixes.ts

@@ -501,14 +501,6 @@ namespace ts.codefix {
                             relativeFileName = getRelativePath(moduleFileName, sourceDirectory);
                         }
 
-                        if (startsWith(relativeFileName, "@types/")) {
-                            relativeFileName = relativeFileName.substr(/*"@types".length*/ 7);
-                            if (relativeFileName.indexOf("__") !== -1) {
-                                // Double underscores are used in DefinitelyTyped to delimit scoped packages.
-                                relativeFileName = "@" + relativeFileName.replace("__", "/");
-                            }
-                        }
-
                         relativeFileName = removeFileExtension(relativeFileName);
                         if (endsWith(relativeFileName, "/index")) {
                             relativeFileName = getDirectoryPath(relativeFileName);
@@ -530,6 +522,8 @@ namespace ts.codefix {
                             catch (e) { }
                         }
 
+                        relativeFileName = getPackageNameFromAtTypesDirectory(relativeFileName);
+
                         return relativeFileName;
                     }
                 }

src/services/pathCompletions.ts

@@ -245,18 +245,15 @@ namespace ts.Completions.PathCompletions {
 
         // Get modules that the type checker picked up
         const ambientModules = map(typeChecker.getAmbientModules(), sym => stripQuotes(sym.name));
-        let nonRelativeModules = filter(ambientModules, moduleName => startsWith(moduleName, fragment));
+        let nonRelativeModuleNames = filter(ambientModules, moduleName => startsWith(moduleName, fragment));
 
         // Nested modules of the form "module-name/sub" need to be adjusted to only return the string
         // after the last '/' that appears in the fragment because that's where the replacement span
         // starts
         if (isNestedModule) {
             const moduleNameWithSeperator = ensureTrailingDirectorySeparator(moduleNameFragment);
-            nonRelativeModules = map(nonRelativeModules, moduleName => {
-                if (startsWith(fragment, moduleNameWithSeperator)) {
-                    return moduleName.substr(moduleNameWithSeperator.length);
-                }
-                return moduleName;
+            nonRelativeModuleNames = map(nonRelativeModuleNames, nonRelativeModuleName => {
+                return removePrefix(nonRelativeModuleName, moduleNameWithSeperator);
             });
         }
 
@@ -264,7 +261,7 @@ namespace ts.Completions.PathCompletions {
         if (!options.moduleResolution || options.moduleResolution === ModuleResolutionKind.NodeJs) {
             for (const visibleModule of enumerateNodeModulesVisibleToScript(host, scriptPath)) {
                 if (!isNestedModule) {
-                    nonRelativeModules.push(visibleModule.moduleName);
+                    nonRelativeModuleNames.push(visibleModule.moduleName);
                 }
                 else if (startsWith(visibleModule.moduleName, moduleNameFragment)) {
                     const nestedFiles = tryReadDirectory(host, visibleModule.moduleDir, supportedTypeScriptExtensions, /*exclude*/ undefined, /*include*/ ["./*"]);
@@ -272,14 +269,14 @@ namespace ts.Completions.PathCompletions {
                         for (let f of nestedFiles) {
                             f = normalizePath(f);
                             const nestedModule = removeFileExtension(getBaseFileName(f));
-                            nonRelativeModules.push(nestedModule);
+                            nonRelativeModuleNames.push(nestedModule);
                         }
                     }
                 }
             }
         }
 
-        return deduplicate(nonRelativeModules);
+        return deduplicate(nonRelativeModuleNames);
     }
 
     export function getTripleSlashReferenceCompletion(sourceFile: SourceFile, position: number, compilerOptions: CompilerOptions, host: LanguageServiceHost): CompletionInfo {