Update kernel status to have a connection status and a kernel status.

This simplified logic quite a bit.

Most of these ideas came from previous work in jupyterlab#4724

Author: jasongrout

packages/console/src/widget.ts

@@ -774,38 +774,23 @@ export class CodeConsole extends Widget {
   /**
    * Handle a change to the kernel.
    */
-  private _onKernelChanged(): void {
+  private async _onKernelChanged(): Promise<void> {
     this.clear();
     if (this._banner) {
       this._banner.dispose();
       this._banner = null;
     }
     this.addBanner();
+    this._handleInfo(await this.session.kernel.info);
   }
 
   /**
    * Handle a change to the kernel status.
    */
-  private _onKernelStatusChanged(): void {
-    if (this.session.status === 'connected') {
-      // we just had a kernel restart or reconnect - reset banner
-      let kernel = this.session.kernel;
-      if (!kernel) {
-        return;
-      }
-      kernel.ready
-        .then(() => {
-          if (this.isDisposed || !kernel || !kernel.info) {
-            return;
-          }
-          this._handleInfo(this.session.kernel.info);
-        })
-        .catch(err => {
-          console.error('could not get kernel info');
-        });
-    } else if (this.session.status === 'restarting') {
+  private async _onKernelStatusChanged(): Promise<void> {
+    if (this.session.status === 'restarting') {
       this.addBanner();
-      this._handleInfo(this.session.kernel.info);
+      this._handleInfo(await this.session.kernel.info);
     }
   }
 

packages/help-extension/src/index.tsx

@@ -190,15 +190,15 @@ function activate(
       return;
     }
     const session = serviceManager.sessions.connectTo(sessionModel);
-    void session.kernel.ready.then(() => {
+
+    void session.kernel.info.then(kernelInfo => {
       // Check the cache second time so that, if two callbacks get scheduled,
       // they don't try to add the same commands.
       if (kernelInfoCache.has(sessionModel.kernel.name)) {
         return;
       }
       // Set the Kernel Info cache.
       const name = session.kernel.name;
-      const kernelInfo = session.kernel.info;
       kernelInfoCache.set(name, kernelInfo);
 
       // Utility function to check if the current widget
@@ -265,7 +265,7 @@ function activate(
 
       // Add the kernel info help_links to the Help menu.
       const kernelGroup: Menu.IItemOptions[] = [];
-      (session.kernel.info.help_links || []).forEach(link => {
+      (kernelInfo.help_links || []).forEach(link => {
         const commandId = `help-menu-${name}:${link.text}`;
         commands.addCommand(commandId, {
           label: link.text,

packages/notebook/src/panel.ts

@@ -196,9 +196,9 @@ export class NotebookPanel extends DocumentWidget<Notebook, INotebookModel> {
       return;
     }
     let { newValue } = args;
-    void newValue.ready.then(() => {
+    void newValue.info.then(info => {
       if (this.model && this.context.session.kernel === newValue) {
-        this._updateLanguage(newValue.info.language_info);
+        this._updateLanguage(info.language_info);
       }
     });
     void this._updateSpec(newValue);