Handle request error code RoslynLspNonFatalRequestFailure (#8935)

Author: RikkiGibson

src/lsptoolshost/server/roslynLanguageClient.ts

@@ -9,6 +9,7 @@ import { LanguageClientOptions, ServerOptions } from 'vscode-languageclient';
 import CompositeDisposable from '../../compositeDisposable';
 import { IDisposable } from '../../disposable';
 import { languageServerOptions } from '../../shared/options';
+import { RoslynLspErrorCodes } from './roslynProtocol';
 
 /**
  * Implementation of the base LanguageClient type that allows for additional items to be disposed of
@@ -41,6 +42,10 @@ export class RoslynLanguageClient extends LanguageClient {
         defaultValue: T,
         showNotification?: boolean
     ) {
+        if (error.code == RoslynLspErrorCodes.nonFatalRequestFailure) {
+            return super.handleFailedRequest(type, token, error, defaultValue, false);
+        }
+
         // Temporarily allow LSP error toasts to be suppressed if configured.
         // There are a few architectural issues preventing us from solving some of the underlying problems,
         // for example Razor cohosting to fix text mismatch issues and unification of serialization libraries

src/lsptoolshost/server/roslynProtocol.ts

@@ -370,3 +370,15 @@ export namespace RefreshSourceGeneratedDocumentNotification {
     export const messageDirection: MessageDirection = MessageDirection.serverToClient;
     export const type = new NotificationType(method);
 }
+
+export namespace RoslynLspErrorCodes {
+    /**
+     * Indicates that the server could not process the request, but that the failure shouldn't be surfaced to the user.
+     * (It's expected that the failure is still logged, however.)
+     *
+     * This is only meant to be used under conditions where we can't fulfill the request, but we think that the failure
+     * is unlikely to be significant to the user (i.e. surface as an actual editor feature failing to function properly.)
+     * For example, if pull diagnostics are requested for a virtual document that was already closed.
+     */
+    export const nonFatalRequestFailure = -30099;
+}