Add noGetErrOnBackgroundUpdate session option to not queue diagnostics check for open files

src/harness/unittests/tsserverProjectSystem.ts

@@ -7445,10 +7445,17 @@ namespace ts.projectSystem {
         });
 
         describe("when event handler is not set but session is created with canUseEvents = true", () => {
-            verifyProjectsUpdatedInBackgroundEvent(createSessionThatUsesEvents);
+            describe("without noGetErrOnBackgroundUpdate, diagnostics for open files are queued", () => {
+                verifyProjectsUpdatedInBackgroundEvent(createSessionThatUsesEvents);
+            });
+
+            describe("with noGetErrOnBackgroundUpdate, diagnostics for open file are not queued", () => {
+                verifyProjectsUpdatedInBackgroundEvent(host => createSessionThatUsesEvents(host, /*noGetErrOnBackgroundUpdate*/ true));
+            });
 
-            function createSessionThatUsesEvents(host: TestServerHost): ProjectsUpdatedInBackgroundEventVerifier {
-                const session = createSession(host, { canUseEvents: true });
+
+            function createSessionThatUsesEvents(host: TestServerHost, noGetErrOnBackgroundUpdate?: boolean): ProjectsUpdatedInBackgroundEventVerifier {
+                const session = createSession(host, { canUseEvents: true, noGetErrOnBackgroundUpdate });
 
                 return {
                     session,
@@ -7480,6 +7487,10 @@ namespace ts.projectSystem {
 
                     // Verified the events, reset them
                     session.clearMessages();
+
+                    if (events.length) {
+                        host.checkTimeoutQueueLength(noGetErrOnBackgroundUpdate ? 0 : 1); // Error checking queued only if not noGetErrOnBackgroundUpdate
+                    }
                 }
             }
         });

src/server/server.ts

@@ -505,6 +505,7 @@ namespace ts.server {
                 canUseEvents: true,
                 suppressDiagnosticEvents,
                 syntaxOnly,
+                noGetErrOnBackgroundUpdate,
                 globalPlugins,
                 pluginProbeLocations,
                 allowLocalPluginLoads,
@@ -939,6 +940,7 @@ namespace ts.server {
     const suppressDiagnosticEvents = hasArgument("--suppressDiagnosticEvents");
     const syntaxOnly = hasArgument("--syntaxOnly");
     const telemetryEnabled = hasArgument(Arguments.EnableTelemetry);
+    const noGetErrOnBackgroundUpdate = hasArgument("--noGetErrOnBackgroundUpdate");
 
     logger.info(`Starting TS Server`);
     logger.info(`Version: ${version}`);

src/server/session.ts

@@ -295,6 +295,7 @@ namespace ts.server {
         suppressDiagnosticEvents?: boolean;
         syntaxOnly?: boolean;
         throttleWaitMilliseconds?: number;
+        noGetErrOnBackgroundUpdate?: boolean;
 
         globalPlugins?: ReadonlyArray<string>;
         pluginProbeLocations?: ReadonlyArray<string>;
@@ -319,6 +320,7 @@ namespace ts.server {
         protected canUseEvents: boolean;
         private suppressDiagnosticEvents?: boolean;
         private eventHandler: ProjectServiceEventHandler;
+        private readonly noGetErrOnBackgroundUpdate?: boolean;
 
         constructor(opts: SessionOptions) {
             this.host = opts.host;
@@ -329,6 +331,7 @@ namespace ts.server {
             this.logger = opts.logger;
             this.canUseEvents = opts.canUseEvents;
             this.suppressDiagnosticEvents = opts.suppressDiagnosticEvents;
+            this.noGetErrOnBackgroundUpdate = opts.noGetErrOnBackgroundUpdate;
 
             const { throttleWaitMilliseconds } = opts;
 
@@ -404,7 +407,7 @@ namespace ts.server {
         private projectsUpdatedInBackgroundEvent(openFiles: string[]): void {
             this.projectService.logger.info(`got projects updated in background, updating diagnostics for ${openFiles}`);
             if (openFiles.length) {
-                if (!this.suppressDiagnosticEvents) {
+                if (!this.suppressDiagnosticEvents && !this.noGetErrOnBackgroundUpdate) {
                     const checkList = this.createCheckList(openFiles);
 
                     // For now only queue error checking for open files. We can change this to include non open files as well

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -8391,6 +8391,7 @@ declare namespace ts.server {
         suppressDiagnosticEvents?: boolean;
         syntaxOnly?: boolean;
         throttleWaitMilliseconds?: number;
+        noGetErrOnBackgroundUpdate?: boolean;
         globalPlugins?: ReadonlyArray<string>;
         pluginProbeLocations?: ReadonlyArray<string>;
         allowLocalPluginLoads?: boolean;
@@ -8410,6 +8411,7 @@ declare namespace ts.server {
         protected canUseEvents: boolean;
         private suppressDiagnosticEvents?;
         private eventHandler;
+        private readonly noGetErrOnBackgroundUpdate?;
         constructor(opts: SessionOptions);
         private sendRequestCompletedEvent;
         private defaultEventHandler;