Loki: Fix autocomplete when re-editing Loki label values (#31828) (#31987)

* Allow re-editing of labels in Loki queries

* Update public/app/plugins/datasource/loki/language_provider.ts

(cherry picked from commit 240e65f693)

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

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

@@ -167,6 +167,25 @@ describe('Language completion provider', () => {
         },
       ]);
     });
+    it('returns label values suggestions from Loki when re-editing', async () => {
+      const datasource = makeMockLokiDatasource({ label1: ['label1_val1', 'label1_val2'], label2: [] });
+      const provider = await getLanguageProvider(datasource);
+      const input = createTypeaheadInput('{label1="label1_v"}', 'label1_v', 'label1', 17, [
+        'attr-value',
+        'context-labels',
+      ]);
+      let result = await provider.provideCompletionItems(input);
+      expect(result.context).toBe('context-label-values');
+      expect(result.suggestions).toEqual([
+        {
+          items: [
+            { label: 'label1_val1', filterText: '"label1_val1"' },
+            { label: 'label1_val2', filterText: '"label1_val2"' },
+          ],
+          label: 'Label values for "label1"',
+        },
+      ]);
+    });
   });
 
   describe('label values', () => {

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

@@ -268,7 +268,7 @@ export default class LokiLanguageProvider extends LanguageProvider {
       selector = EMPTY_SELECTOR;
     }
 
-    if (!isValueStart && selector === EMPTY_SELECTOR) {
+    if (!labelKey && selector === EMPTY_SELECTOR) {
       // start task gets all labels
       await this.start();
       const allLabels = this.getLabelKeys();