Session: don't return undefined if a response is required

src/harness/unittests/projectErrors.ts

@@ -4,12 +4,12 @@
 
 namespace ts.projectSystem {
     describe("Project errors", () => {
-        function checkProjectErrors(projectFiles: server.ProjectFilesWithTSDiagnostics, expectedErrors: string[]) {
+        function checkProjectErrors(projectFiles: server.ProjectFilesWithTSDiagnostics, expectedErrors: ReadonlyArray<string>): void {
             assert.isTrue(projectFiles !== undefined, "missing project files");
             checkProjectErrorsWorker(projectFiles.projectErrors, expectedErrors);
         }
 
-        function checkProjectErrorsWorker(errors: Diagnostic[], expectedErrors: string[]) {
+        function checkProjectErrorsWorker(errors: ReadonlyArray<Diagnostic>, expectedErrors: ReadonlyArray<string>): void {
             assert.equal(errors ? errors.length : 0, expectedErrors.length, `expected ${expectedErrors.length} error in the list`);
             if (expectedErrors.length) {
                 for (let i = 0; i < errors.length; i++) {

src/server/editorServices.ts

@@ -22,7 +22,7 @@ namespace ts.server {
 
     export interface ConfigFileDiagEvent {
         eventName: typeof ConfigFileDiagEvent;
-        data: { triggerFile: string, configFileName: string, diagnostics: Diagnostic[] };
+        data: { triggerFile: string, configFileName: string, diagnostics: ReadonlyArray<Diagnostic> };
     }
 
     export interface ProjectLanguageServiceStateEvent {
@@ -200,7 +200,7 @@ namespace ts.server {
     /**
      * This helper function processes a list of projects and return the concatenated, sortd and deduplicated output of processing each project.
      */
-    export function combineProjectOutput<T>(projects: Project[], action: (project: Project) => T[], comparer?: (a: T, b: T) => number, areEqual?: (a: T, b: T) => boolean) {
+    export function combineProjectOutput<T>(projects: ReadonlyArray<Project>, action: (project: Project) => ReadonlyArray<T>, comparer?: (a: T, b: T) => number, areEqual?: (a: T, b: T) => boolean) {
         const result = flatMap(projects, action).sort(comparer);
         return projects.length > 1 ? deduplicate(result, areEqual) : result;
     }
@@ -220,14 +220,14 @@ namespace ts.server {
 
     interface OpenConfigFileResult {
         success: boolean;
-        errors?: Diagnostic[];
+        errors?: ReadonlyArray<Diagnostic>;
 
         project?: ConfiguredProject;
     }
 
     export interface OpenConfiguredProjectResult {
         configFileName?: NormalizedPath;
-        configFileErrors?: Diagnostic[];
+        configFileErrors?: ReadonlyArray<Diagnostic>;
     }
 
     interface FilePropertyReader<T> {
@@ -1102,18 +1102,18 @@ namespace ts.server {
             }
         }
 
-        private reportConfigFileDiagnostics(configFileName: string, diagnostics: Diagnostic[], triggerFile: string) {
+        private reportConfigFileDiagnostics(configFileName: string, diagnostics: ReadonlyArray<Diagnostic>, triggerFile: string) {
             if (!this.eventHandler) {
                 return;
             }
 
             this.eventHandler(<ConfigFileDiagEvent>{
                 eventName: ConfigFileDiagEvent,
-                data: { configFileName, diagnostics: diagnostics || [], triggerFile }
+                data: { configFileName, diagnostics: diagnostics || emptyArray, triggerFile }
             });
         }
 
-        private createAndAddConfiguredProject(configFileName: NormalizedPath, projectOptions: ProjectOptions, configFileErrors: Diagnostic[], clientFileName?: string) {
+        private createAndAddConfiguredProject(configFileName: NormalizedPath, projectOptions: ProjectOptions, configFileErrors: ReadonlyArray<Diagnostic>, clientFileName?: string) {
             const sizeLimitExceeded = this.exceededTotalSizeLimitForNonTsFiles(configFileName, projectOptions.compilerOptions, projectOptions.files, fileNamePropertyReader);
             const project = new ConfiguredProject(
                 configFileName,
@@ -1145,7 +1145,7 @@ namespace ts.server {
             }
         }
 
-        private addFilesToProjectAndUpdateGraph<T>(project: ConfiguredProject | ExternalProject, files: T[], propertyReader: FilePropertyReader<T>, clientFileName: string, typeAcquisition: TypeAcquisition, configFileErrors: Diagnostic[]): void {
+        private addFilesToProjectAndUpdateGraph<T>(project: ConfiguredProject | ExternalProject, files: T[], propertyReader: FilePropertyReader<T>, clientFileName: string, typeAcquisition: TypeAcquisition, configFileErrors: ReadonlyArray<Diagnostic>): void {
             let errors: Diagnostic[];
             for (const f of files) {
                 const rootFilename = propertyReader.getFileName(f);
@@ -1458,7 +1458,7 @@ namespace ts.server {
 
         openClientFileWithNormalizedPath(fileName: NormalizedPath, fileContent?: string, scriptKind?: ScriptKind, hasMixedContent?: boolean, projectRootPath?: NormalizedPath): OpenConfiguredProjectResult {
             let configFileName: NormalizedPath;
-            let configFileErrors: Diagnostic[];
+            let configFileErrors: ReadonlyArray<Diagnostic>;
 
             let project: ConfiguredProject | ExternalProject = this.findContainingExternalProject(fileName);
             if (!project) {

src/server/project.ts

@@ -54,7 +54,7 @@ namespace ts.server {
 
     /* @internal */
     export interface ProjectFilesWithTSDiagnostics extends protocol.ProjectFiles {
-        projectErrors: Diagnostic[];
+        projectErrors: ReadonlyArray<Diagnostic>;
     }
 
     export class UnresolvedImportsMap {
@@ -147,7 +147,7 @@ namespace ts.server {
 
         private typingFiles: SortedReadonlyArray<string>;
 
-        protected projectErrors: Diagnostic[];
+        protected projectErrors: ReadonlyArray<Diagnostic>;
 
         public typesVersion = 0;
 
@@ -1045,7 +1045,7 @@ namespace ts.server {
             return getDirectoryPath(this.getConfigFilePath());
         }
 
-        setProjectErrors(projectErrors: Diagnostic[]) {
+        setProjectErrors(projectErrors: ReadonlyArray<Diagnostic>) {
             this.projectErrors = projectErrors;
         }
 
@@ -1189,7 +1189,7 @@ namespace ts.server {
             return this.typeAcquisition;
         }
 
-        setProjectErrors(projectErrors: Diagnostic[]) {
+        setProjectErrors(projectErrors: ReadonlyArray<Diagnostic>) {
             this.projectErrors = projectErrors;
         }
 

src/server/protocol.ts

@@ -914,7 +914,7 @@ namespace ts.server.protocol {
         /**
          * An array of span groups (one per file) that refer to the item to be renamed.
          */
-        locs: SpanGroup[];
+        locs: ReadonlyArray<SpanGroup>;
     }
 
     /**