[Discover] Fix sorting by _score behavior

src/plugins/discover/public/__mocks__/config.ts

@@ -6,12 +6,15 @@
  * Side Public License, v 1.
  */
 
-import { IUiSettingsClient } from '../../../../core/public';
+import { IUiSettingsClient } from 'kibana/public';
+import { SORT_DEFAULT_ORDER_SETTING } from '../../common';
 
 export const configMock = ({
   get: (key: string) => {
     if (key === 'defaultIndex') {
       return 'the-index-pattern-id';
+    } else if (key === SORT_DEFAULT_ORDER_SETTING) {
+      return 'desc';
     }
 
     return '';

src/plugins/discover/public/application/angular/doc_table/actions/columns.test.ts

@@ -0,0 +1,78 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import { getStateColumnActions } from './columns';
+import { configMock } from '../../../../__mocks__/config';
+import { indexPatternMock } from '../../../../__mocks__/index_pattern';
+import { indexPatternsMock } from '../../../../__mocks__/index_patterns';
+import { Capabilities } from '../../../../../../../core/types';
+import { AppState } from '../../discover_state';
+
+function getStateColumnAction(state: {}, setAppState: (state: Partial<AppState>) => void) {
+  return getStateColumnActions({
+    capabilities: ({
+      discover: {
+        save: false,
+      },
+    } as unknown) as Capabilities,
+    config: configMock,
+    indexPattern: indexPatternMock,
+    indexPatterns: indexPatternsMock,
+    useNewFieldsApi: true,
+    setAppState,
+    state,
+  });
+}
+
+describe('Test column actions', () => {
+  test('getStateColumnActions with empty state', () => {
+    const setAppState = jest.fn();
+    const actions = getStateColumnAction({}, setAppState);
+
+    actions.onAddColumn('_score');
+    expect(setAppState).toHaveBeenCalledWith({ columns: ['_score'], sort: [['_score', 'desc']] });
+    actions.onAddColumn('test');
+    expect(setAppState).toHaveBeenCalledWith({ columns: ['test'] });
+  });
+  test('getStateColumnActions with columns and sort in state', () => {
+    const setAppState = jest.fn();
+    const actions = getStateColumnAction(
+      { columns: ['first', 'second'], sort: [['first', 'desc']] },
+      setAppState
+    );
+
+    actions.onAddColumn('_score');
+    expect(setAppState).toHaveBeenCalledWith({
+      columns: ['first', 'second', '_score'],
+      sort: [['first', 'desc']],
+    });
+    setAppState.mockClear();
+    actions.onAddColumn('third');
+    expect(setAppState).toHaveBeenCalledWith({
+      columns: ['first', 'second', 'third'],
+      sort: [['first', 'desc']],
+    });
+    setAppState.mockClear();
+    actions.onRemoveColumn('first');
+    expect(setAppState).toHaveBeenCalledWith({
+      columns: ['second'],
+      sort: [],
+    });
+    setAppState.mockClear();
+    actions.onSetColumns(['first', 'second', 'third']);
+    expect(setAppState).toHaveBeenCalledWith({
+      columns: ['first', 'second', 'third'],
+    });
+    setAppState.mockClear();
+
+    actions.onMoveColumn('second', 0);
+    expect(setAppState).toHaveBeenCalledWith({
+      columns: ['second', 'first'],
+    });
+  });
+});

src/plugins/discover/public/application/angular/doc_table/actions/columns.ts

@@ -5,10 +5,11 @@
  * in compliance with, at your election, the Elastic License 2.0 or the Server
  * Side Public License, v 1.
  */
-import { Capabilities } from 'kibana/public';
+import { Capabilities, IUiSettingsClient } from 'kibana/public';
 import { popularizeField } from '../../../helpers/popularize_field';
 import { IndexPattern, IndexPatternsContract } from '../../../../kibana_services';
 import { AppState } from '../../discover_state';
+import { SORT_DEFAULT_ORDER_SETTING } from '../../../../../common';
 
 /**
  * Helper function to provide a fallback to a single _source column if the given array of columns
@@ -54,13 +55,15 @@ export function moveColumn(columns: string[], columnName: string, newIndex: numb
 
 export function getStateColumnActions({
   capabilities,
+  config,
   indexPattern,
   indexPatterns,
   useNewFieldsApi,
   setAppState,
   state,
 }: {
   capabilities: Capabilities;
+  config: IUiSettingsClient;
   indexPattern: IndexPattern;
   indexPatterns: IndexPatternsContract;
   useNewFieldsApi: boolean;
@@ -72,7 +75,10 @@ export function getStateColumnActions({
       popularizeField(indexPattern, columnName, indexPatterns);
     }
     const columns = addColumn(state.columns || [], columnName, useNewFieldsApi);
-    setAppState({ columns });
+    const defaultOrder = config.get(SORT_DEFAULT_ORDER_SETTING);
+    const sort =
+      columnName === '_score' && !state.sort?.length ? [['_score', defaultOrder]] : state.sort;
+    setAppState({ columns, sort });
   }
 
   function onRemoveColumn(columnName: string) {

src/plugins/discover/public/application/components/discover.tsx

@@ -104,13 +104,14 @@ export function Discover({
     () =>
       getStateColumnActions({
         capabilities,
+        config,
         indexPattern,
         indexPatterns,
         setAppState,
         state,
         useNewFieldsApi,
       }),
-    [capabilities, indexPattern, indexPatterns, setAppState, state, useNewFieldsApi]
+    [capabilities, config, indexPattern, indexPatterns, setAppState, state, useNewFieldsApi]
   );
 
   const onOpenInspector = useCallback(() => {