added API to check extension status

src/extension.ts

@@ -110,6 +110,17 @@ export interface XMLExtensionApi {
    * @returns None
    */
   removeXMLFileAssociations(fileAssociations: XMLFileAssociation[]): void;
+  /**
+   * Returns the status of the Language Client
+   * 
+   * @remarks
+   * An example is to call this API:
+   * ```ts
+   * isReady()
+   * ``` 
+   * @returns Boolean
+   */
+  isReady(): boolean;
 }
 
 namespace TagCloseRequest {
@@ -196,6 +207,7 @@ export function activate(context: ExtensionContext) {
     let languageClient = new LanguageClient('xml', 'XML Support', serverOptions, clientOptions);
     let toDispose = context.subscriptions;
     let disposable = languageClient.start();
+    let clientIsReady = false;
     toDispose.push(disposable);
     languageClient.onReady().then(() => {
       //Detect JDK configuration changes
@@ -233,7 +245,7 @@ export function activate(context: ExtensionContext) {
           onExtensionChange(extensions.all);
         });
       }
-
+      clientIsReady = true;
     });
     languages.setLanguageConfiguration('xml', getIndentationRules());
     languages.setLanguageConfiguration('xsl', getIndentationRules());
@@ -284,6 +296,10 @@ export function activate(context: ExtensionContext) {
         });
         languageClient.sendNotification(DidChangeConfigurationNotification.type, { settings: getXMLSettings(requirements.java_home) });
         onConfigurationChange();
+      },
+      // return if Language Client is ready
+      isReady: () => {
+        return clientIsReady;
       }
     };