Introduce error in new db panel

extensions/ql-vscode/src/databases/ui/db-tree-data-provider.ts

@@ -1,6 +1,6 @@
 import { logger } from '../../logging';
 import { ProviderResult, TreeDataProvider, TreeItem } from 'vscode';
-import { DbTreeViewItem } from './db-tree-view-item';
+import { createDbTreeViewItemWarning, DbTreeViewItem } from './db-tree-view-item';
 import { DbManager } from '../db-manager';
 
 export class DbTreeDataProvider implements TreeDataProvider<DbTreeViewItem> {
@@ -41,6 +41,12 @@ export class DbTreeDataProvider implements TreeDataProvider<DbTreeViewItem> {
     // This will be fleshed out in a future change.
     void logger.log(`Creating database tree with ${dbItems.length} items`);
 
-    return [];
+    // Add a sample warning as a proof of concept.
+    const warningTreeViewItem = createDbTreeViewItemWarning(
+      'There was an error',
+      'Fix it'
+    );
+
+    return [warningTreeViewItem];
   }
 }

extensions/ql-vscode/src/databases/ui/db-tree-view-item.ts

@@ -2,11 +2,13 @@ import * as vscode from 'vscode';
 import { DbItem } from '../db-item';
 
 /**
- * Represents an item in the database tree view.
+ * Represents an item in the database tree view. This item could be 
+ * representing an actual database item or a warning.
  */
 export class DbTreeViewItem extends vscode.TreeItem {
   constructor(
-    public readonly dbItem: DbItem,
+    public readonly dbItem: DbItem | undefined,
+    public readonly iconPath: vscode.ThemeIcon,
     public readonly label: string,
     public readonly tooltip: string,
     public readonly collapsibleState: vscode.TreeItemCollapsibleState,
@@ -15,3 +17,14 @@ export class DbTreeViewItem extends vscode.TreeItem {
     super(label, collapsibleState);
   }
 }
+
+export function createDbTreeViewItemWarning(label: string, tooltip: string): DbTreeViewItem {
+  return new DbTreeViewItem(
+    undefined,
+    new vscode.ThemeIcon('warning', new vscode.ThemeColor('problemsWarningIcon.foreground')),
+    label,
+    tooltip,
+    vscode.TreeItemCollapsibleState.None,
+    []
+  );
+}