DatasourceSrv: Fix getInstanceSettings for type-only datasource references (#110612)

• Add handling for type-only refs like {type: 'prometheus'} in getInstanceSettings()
• Ensure consistency with get() method behavior
• Add test case verifying both methods return same results for type-only refs

public/app/features/plugins/datasource_srv.test.ts

@@ -299,6 +299,19 @@ describe('datasource_srv', () => {
         const settings = dataSourceSrv.getInstanceSettings(runtimeDataSource.name);
         expect(settings).toBe(undefined);
       });
+
+      it('should handle type-only datasource references consistently', async () => {
+        const typeOnlyRef = { type: 'jaeger-db' };
+
+        const datasource = await dataSourceSrv.get(typeOnlyRef);
+        const settings = dataSourceSrv.getInstanceSettings(typeOnlyRef);
+
+        expect(datasource.uid).toBe('uid-code-Jaeger');
+        expect(datasource.type).toBe('jaeger-db');
+        expect(settings?.uid).toBe(datasource.uid);
+        expect(settings?.type).toBe(datasource.type);
+        expect(settings?.name).toBe('Jaeger');
+      });
     });
 
     describe('when loading datasource', () => {

public/app/features/plugins/datasource_srv.ts

@@ -107,6 +107,14 @@ export class DatasourceSrv implements DataSourceService {
     }
 
     if (nameOrUid === 'default' || nameOrUid == null) {
+      // Handle type-only datasource references (e.g., {type: 'prometheus'})
+      if (isDatasourceRef(ref) && ref.type) {
+        const ds = this.findDatasourceByType(ref.type);
+        if (ds) {
+          return ds;
+        }
+      }
+      // Fall back to default datasource if no type match found
       return this.settingsMapByUid[this.defaultName] ?? this.settingsMapByName[this.defaultName];
     }
 
@@ -143,13 +151,12 @@ export class DatasourceSrv implements DataSourceService {
   get(ref?: string | DataSourceRef | null, scopedVars?: ScopedVars): Promise<DataSourceApi> {
     let nameOrUid = getNameOrUid(ref);
     if (!nameOrUid) {
-      // type exists, but not the other properties
-      if (isDatasourceRef(ref)) {
-        const settings = this.getList({ type: ref.type });
-        if (!settings?.length) {
+      // Handle type-only datasource references
+      if (isDatasourceRef(ref) && ref.type) {
+        const ds = this.findDatasourceByType(ref.type);
+        if (!ds) {
           return Promise.reject('no datasource of type');
         }
-        const ds = settings.find((v) => v.isDefault) ?? settings[0];
         return this.get(ds.uid);
       }
       return this.get(this.defaultName);
@@ -184,6 +191,18 @@ export class DatasourceSrv implements DataSourceService {
     return this.loadDatasource(nameOrUid);
   }
 
+  /**
+   * Finds the best datasource instance settings for a given type.
+   * Prefers the default datasource of that type, otherwise returns the first one found.
+   */
+  private findDatasourceByType(type: string): DataSourceInstanceSettings | undefined {
+    const settings = this.getList({ type });
+    if (!settings?.length) {
+      return undefined;
+    }
+    return settings.find((v) => v.isDefault) ?? settings[0];
+  }
+
   async loadDatasource(key: string): Promise<DataSourceApi> {
     if (this.datasources[key]) {
       return Promise.resolve(this.datasources[key]);