Added polling to ready to merge widget state

Adds polling to get the updated merge trains count

app/assets/javascripts/vue_merge_request_widget/components/states/ready_to_merge.vue

@@ -16,8 +16,10 @@ import readyToMergeMixin from 'ee_else_ce/vue_merge_request_widget/mixins/ready_
 import readyToMergeQuery from 'ee_else_ce/vue_merge_request_widget/queries/states/ready_to_merge.query.graphql';
 import { refreshUserMergeRequestCounts } from '~/commons/nav/user_merge_requests';
 import createFlash from '~/flash';
+import { secondsToMilliseconds } from '~/lib/utils/datetime_utility';
 import simplePoll from '~/lib/utils/simple_poll';
 import { __ } from '~/locale';
+import SmartInterval from '~/smart_interval';
 import glFeatureFlagMixin from '~/vue_shared/mixins/gl_feature_flags_mixin';
 import MergeRequest from '../../../merge_request';
 import { AUTO_MERGE_STRATEGIES, DANGER, INFO, WARNING } from '../../constants';
@@ -66,6 +68,10 @@ export default {
         this.isSquashReadOnly = data.project.squashReadOnly;
         this.squashCommitMessage = data.project.mergeRequest.defaultSquashCommitMessage;
         this.loading = false;
+
+        if (this.state.mergeTrainsCount !== null) {
+          this.initPolling();
+        }
       },
     },
   },
@@ -291,8 +297,23 @@ export default {
     if (this.glFeatures.mergeRequestWidgetGraphql) {
       eventHub.$off('ApprovalUpdated', this.updateGraphqlState);
     }
+
+    if (this.pollingInterval) {
+      this.pollingInterval.destroy();
+    }
   },
   methods: {
+    initPolling() {
+      const startingPollInterval = secondsToMilliseconds(5);
+
+      this.pollingInterval = new SmartInterval({
+        callback: () => this.$apollo.queries.state.refetch(),
+        startingInterval: startingPollInterval,
+        maxInterval: startingPollInterval + secondsToMilliseconds(4 * 60),
+        hiddenInterval: secondsToMilliseconds(6 * 60),
+        incrementByFactorOf: 2,
+      });
+    },
     updateGraphqlState() {
       return this.$apollo.queries.state.refetch();
     },

ee/spec/features/merge_trains/user_adds_merge_request_to_merge_train_spec.rb

@@ -85,12 +85,6 @@ RSpec.describe 'User adds a merge request to a merge train', :js do
     context "when user clicks 'Remove from merge train' button" do
       before do
         click_link 'Remove from merge train'
-        # Currently, this page shows "Add to merge train" button instead of "Start merge train",
-        # even though the merge train is empty.
-        # This likely is caused by the stale cache in client side. Frontend
-        # would need to refresh the mergiability data, specifically `stateData.mergeTrainsCount` periodically e.g. polling.
-        # As a workaround, we're doing a hard reload by executing `visit` here.
-        visit project_merge_request_path(project, merge_request)
       end
 
       it 'cancels automatic merge' do