Loki: Fix `show context` not working in some occasions (#52458)

* added missing `languageProvider.start` call

* moved `languageProvider.start`

.betterer.results

@@ -7646,8 +7646,7 @@ exports[`better eslint`] = {
       [0, 0, 0, "Unexpected any. Specify a different type.", "10"],
       [0, 0, 0, "Unexpected any. Specify a different type.", "11"],
       [0, 0, 0, "Unexpected any. Specify a different type.", "12"],
-      [0, 0, 0, "Unexpected any. Specify a different type.", "13"],
-      [0, 0, 0, "Unexpected any. Specify a different type.", "14"]
+      [0, 0, 0, "Unexpected any. Specify a different type.", "13"]
     ],
     "public/app/plugins/datasource/loki/datasource.ts:5381": [
       [0, 0, 0, "Unexpected any. Specify a different type.", "0"],

public/app/plugins/datasource/loki/datasource.test.ts

@@ -703,7 +703,7 @@ describe('LokiDatasource', () => {
 
   describe('prepareLogRowContextQueryTarget', () => {
     const ds = createLokiDSForTests();
-    it('creates query with only labels from /labels API', () => {
+    it('creates query with only labels from /labels API', async () => {
       const row: LogRowModel = {
         rowIndex: 0,
         dataFrame: new MutableDataFrame({
@@ -717,15 +717,39 @@ describe('LokiDatasource', () => {
         }),
         labels: { bar: 'baz', foo: 'uniqueParsedLabel' },
         uid: '1',
-      } as any;
+      } as unknown as LogRowModel;
 
       //Mock stored labels to only include "bar" label
+      jest.spyOn(ds.languageProvider, 'start').mockImplementation(() => Promise.resolve([]));
       jest.spyOn(ds.languageProvider, 'getLabelKeys').mockImplementation(() => ['bar']);
-      const contextQuery = ds.prepareLogRowContextQueryTarget(row, 10, 'BACKWARD');
+      const contextQuery = await ds.prepareLogRowContextQueryTarget(row, 10, 'BACKWARD');
 
       expect(contextQuery.query.expr).toContain('baz');
       expect(contextQuery.query.expr).not.toContain('uniqueParsedLabel');
     });
+
+    it('should call languageProvider.start to fetch labels', async () => {
+      const row: LogRowModel = {
+        rowIndex: 0,
+        dataFrame: new MutableDataFrame({
+          fields: [
+            {
+              name: 'ts',
+              type: FieldType.time,
+              values: [0],
+            },
+          ],
+        }),
+        labels: { bar: 'baz', foo: 'uniqueParsedLabel' },
+        uid: '1',
+      } as unknown as LogRowModel;
+
+      //Mock stored labels to only include "bar" label
+      jest.spyOn(ds.languageProvider, 'start').mockImplementation(() => Promise.resolve([]));
+      await ds.prepareLogRowContextQueryTarget(row, 10, 'BACKWARD');
+
+      expect(ds.languageProvider.start).toBeCalled();
+    });
   });
 
   describe('logs volume data provider', () => {

public/app/plugins/datasource/loki/datasource.ts

@@ -431,10 +431,10 @@ export class LokiDatasource
     return Math.ceil(date.valueOf() * 1e6);
   }
 
-  getLogRowContext = (row: LogRowModel, options?: RowContextOptions): Promise<{ data: DataFrame[] }> => {
+  getLogRowContext = async (row: LogRowModel, options?: RowContextOptions): Promise<{ data: DataFrame[] }> => {
     const direction = (options && options.direction) || 'BACKWARD';
     const limit = (options && options.limit) || 10;
-    const { query, range } = this.prepareLogRowContextQueryTarget(row, limit, direction);
+    const { query, range } = await this.prepareLogRowContextQueryTarget(row, limit, direction);
 
     const processDataFrame = (frame: DataFrame): DataFrame => {
       // log-row-context requires specific field-names to work, so we set them here: "ts", "line", "id"
@@ -497,11 +497,13 @@ export class LokiDatasource
     );
   };
 
-  prepareLogRowContextQueryTarget = (
+  prepareLogRowContextQueryTarget = async (
     row: LogRowModel,
     limit: number,
     direction: 'BACKWARD' | 'FORWARD'
-  ): { query: LokiQuery; range: TimeRange } => {
+  ): Promise<{ query: LokiQuery; range: TimeRange }> => {
+    // need to await the languageProvider to be started to have all labels. This call is not blocking after it has been called once.
+    await this.languageProvider.start();
     const labels = this.languageProvider.getLabelKeys();
     const expr = Object.keys(row.labels)
       .map((label: string) => {