Warn users about too many files processed in the workspace

Extension/src/LanguageServer/client.ts

@@ -1744,7 +1744,7 @@ export class DefaultClient implements Client {
         languageClient = new LanguageClient(`cpptools`, serverOptions, clientOptions);
         languageClient.onNotification(DebugProtocolNotification, logDebugProtocol);
         languageClient.onNotification(DebugLogNotification, logLocalized);
-        languageClient.onNotification(LogTelemetryNotification, (e) => this.logTelemetry(e));
+        languageClient.onNotification(LogTelemetryNotification, (e) => void this.logTelemetry(e));
         languageClient.onNotification(ShowMessageWindowNotification, showMessageWindow);
         languageClient.registerProposedFeatures();
         await languageClient.start();
@@ -2778,10 +2778,38 @@ export class DefaultClient implements Client {
         }
     }
 
-    private logTelemetry(notificationBody: TelemetryPayload): void {
+    private excessiveFilesWarningShown: boolean = false;
+    private async logTelemetry(notificationBody: TelemetryPayload): Promise<void> {
         if (notificationBody.event === "includeSquiggles" && this.configurationProvider && notificationBody.properties) {
             notificationBody.properties["providerId"] = this.configurationProvider;
         }
+
+        const showExcessiveFilesWarning = new PersistentWorkspaceState<boolean>('CPP.showExcessiveFilesWarning', true);
+        if (!this.excessiveFilesWarningShown && showExcessiveFilesWarning.Value && notificationBody.event === 'ParsingStats') {
+            const filesDiscovered = notificationBody.metrics?.filesDiscovered ?? 0;
+            const parsableFiles = notificationBody.metrics?.parsableFiles ?? 0;
+            if (filesDiscovered > 250000 || parsableFiles > 100000) {
+                // According to telemetry, less than 3% of workspaces have this many files so it seems like a reasonable threshold.
+
+                const message = localize(
+                    "parsing.stats.large.project",
+                    'Enumerated {0} files with {1} C/C++ source files detected. You may want to consider excluding some files for better performance.',
+                    filesDiscovered,
+                    parsableFiles);
+                const learnMore = localize('learn.more', 'Learn More');
+                const dontShowAgain = localize('dont.show.again', 'Don\'t Show Again');
+
+                // We only want to show this once per session.
+                this.excessiveFilesWarningShown = true;
+                const response = await vscode.window.showInformationMessage(message, learnMore, dontShowAgain);
+
+                if (response === dontShowAgain) {
+                    showExcessiveFilesWarning.Value = false;
+                } else if (response === learnMore) {
+                    void vscode.commands.executeCommand('vscode.open', vscode.Uri.parse('https://go.microsoft.com/fwlink/?linkid=2333292'));
+                }
+            }
+        }
         telemetry.logLanguageServerEvent(notificationBody.event, notificationBody.properties, notificationBody.metrics);
     }