DashboardScene: Re-add support for default datasource var (#94806)

re-add support for default datasource var

public/app/features/dashboard-scene/utils/variables.test.ts

@@ -251,6 +251,7 @@ describe('when creating variables objects', () => {
       isMulti: true,
       description: null,
       hide: 0,
+      defaultOptionEnabled: false,
     });
   });
 
@@ -673,6 +674,49 @@ describe('when creating variables objects', () => {
       type: 'datasource',
       value: '',
       isMulti: true,
+      defaultOptionEnabled: false,
+    });
+  });
+
+  it('should handle datasource variable with default selected', () => {
+    // @ts-expect-error
+    const variable: TypedVariableModel = {
+      id: 'query1',
+      current: {
+        text: 'default',
+        value: 'default',
+        selected: true,
+      },
+      name: 'query1',
+      type: 'datasource',
+      global: false,
+      regex: '/^gdev/',
+      options: [],
+      query: 'prometheus',
+      multi: true,
+      includeAll: true,
+      refresh: 1,
+      allValue: 'Custom all',
+    };
+
+    const migrated = createSceneVariableFromVariableModel(variable);
+    const { key, ...rest } = migrated.state;
+
+    expect(migrated).toBeInstanceOf(DataSourceVariable);
+    expect(rest).toEqual({
+      allValue: 'Custom all',
+      defaultToAll: true,
+      includeAll: true,
+      label: undefined,
+      name: 'query1',
+      options: [],
+      pluginId: 'prometheus',
+      regex: '/^gdev/',
+      text: 'default',
+      type: 'datasource',
+      value: 'default',
+      isMulti: true,
+      defaultOptionEnabled: true,
     });
   });
 });

public/app/features/dashboard-scene/utils/variables.ts

@@ -18,6 +18,8 @@ import { SnapshotVariable } from '../serialization/custom-variables/SnapshotVari
 
 import { getCurrentValueForOldIntervalModel, getIntervalsFromQueryString } from './utils';
 
+const DEFAULT_DATASOURCE = 'default';
+
 export function createVariablesForDashboard(oldModel: DashboardModel) {
   const variableObjects = oldModel.templating.list
     .map((v) => {
@@ -189,6 +191,7 @@ export function createSceneVariableFromVariableModel(variable: TypedVariableMode
       skipUrlSync: variable.skipUrlSync,
       isMulti: variable.multi,
       hide: variable.hide,
+      defaultOptionEnabled: variable.current?.value === DEFAULT_DATASOURCE && variable.current?.text === 'default',
     });
   } else if (variable.type === 'interval') {
     const intervals = getIntervalsFromQueryString(variable.query);