Support GraphQL subscription for weight update

A GraphQL subscription for issuable weight update is added.

Changelog: added
EE: true

app/graphql/graphql_triggers.rb

@@ -21,3 +21,5 @@ def self.issuable_dates_updated(issuable)
     GitlabSchema.subscriptions.trigger('issuableDatesUpdated', { issuable_id: issuable.to_gid }, issuable)
   end
 end
+
+GraphqlTriggers.prepend_mod

app/graphql/types/subscription_type.rb

@@ -25,3 +25,5 @@ class SubscriptionType < ::Types::BaseObject
           description: 'Triggered when the reviewers of a merge request are updated.'
   end
 end
+
+Types::SubscriptionType.prepend_mod

ee/app/graphql/ee/graphql_triggers.rb

+# frozen_string_literal: true
+
+module EE
+  module GraphqlTriggers
+    extend ActiveSupport::Concern
+    prepended do
+      def self.issuable_weight_updated(issuable)
+        ::GitlabSchema.subscriptions.trigger('issuableWeightUpdated', { issuable_id: issuable.to_gid }, issuable)
+      end
+    end
+  end
+end

ee/app/graphql/ee/types/subscription_type.rb

+# frozen_string_literal: true
+
+module EE
+  module Types
+    module SubscriptionType
+      extend ActiveSupport::Concern
+
+      prepended do
+        field :issuable_weight_updated, subscription: Subscriptions::IssuableUpdated, null: true,
+                                        description: 'Triggered when the weight of an issuable is updated.'
+      end
+    end
+  end
+end

ee/app/services/ee/issues/update_service.rb

@@ -36,6 +36,7 @@ def handle_changes(issue, _options)
         super
 
         handle_iteration_change(issue)
+        handle_weight_change(issue)
       end
 
       override :before_update
@@ -60,6 +61,12 @@ def handle_iteration_change(issue)
         send_iteration_change_notification(issue)
       end
 
+      def handle_weight_change(issue)
+        return unless issue.previous_changes.key?(:weight)
+
+        ::GraphqlTriggers.issuable_weight_updated(issue)
+      end
+
       def send_iteration_change_notification(issue)
         if issue.iteration.nil?
           notification_service.async.removed_iteration_issue(issue, current_user)

ee/spec/graphql/graphql_triggers_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe GraphqlTriggers do
+  describe '.issuable_weight_updated' do
+    let(:work_item) { create(:work_item) }
+
+    it 'triggers the issuableWeightUpdated subscription' do
+      expect(GitlabSchema.subscriptions).to receive(:trigger).with(
+        'issuableWeightUpdated',
+        { issuable_id: work_item.to_gid },
+        work_item
+      ).and_call_original
+
+      ::GraphqlTriggers.issuable_weight_updated(work_item)
+    end
+  end
+end

ee/spec/graphql/types/subscription_type_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe GitlabSchema.types['Subscription'] do
+  it 'has the expected fields' do
+    expected_fields = %i[
+      issuable_weight_updated
+    ]
+
+    expect(described_class).to include_graphql_fields(*expected_fields)
+  end
+end

ee/spec/services/ee/issues/update_service_spec.rb

@@ -20,6 +20,40 @@ def update_issue(opts)
       described_class.new(project: project, current_user: user, params: opts).execute(issue)
     end
 
+    context 'updating weight' do
+      before do
+        stub_licensed_features(issue_weights: true)
+
+        project.add_developer(user)
+
+        issue.update!(weight: 1)
+      end
+
+      context 'when weight is changed' do
+        it "triggers 'issuableWeightUpdated' for issuable weight update subscription" do
+          expect(GraphqlTriggers).to receive(:issuable_weight_updated).with(issue).and_call_original
+
+          update_issue(weight: nil)
+        end
+      end
+
+      context 'when weight remains unchanged' do
+        it "does not trigger 'issuableWeightUpdated' for issuable weight update subscription" do
+          expect(GraphqlTriggers).not_to receive(:issuable_weight_updated)
+
+          update_issue(weight: 1)
+        end
+      end
+
+      context 'when weight param is not provided' do
+        it "does not trigger 'issuableWeightUpdated' for issuable weight update subscription" do
+          expect(GraphqlTriggers).not_to receive(:issuable_weight_updated)
+
+          update_issue(title: "foobar")
+        end
+      end
+    end
+
     context 'refresh epic dates' do
       before do
         issue.update!(epic: epic)

ee/spec/services/work_items/update_service_spec.rb

@@ -11,6 +11,18 @@
   let(:current_user) { developer }
 
   describe '#execute' do
+    let(:service) do
+      described_class.new(
+        project: project,
+        current_user: current_user,
+        params: {},
+        spam_params: spam_params,
+        widget_params: widget_params
+      )
+    end
+
+    subject { service.execute(work_item) }
+
     before do
       stub_spam_services
     end
@@ -22,17 +34,7 @@
         }
       end
 
-      let(:service) do
-        described_class.new(
-          project: project,
-          current_user: current_user,
-          params: {},
-          spam_params: spam_params,
-          widget_params: widget_params
-        )
-      end
-
-      let(:service_execute) { service.execute(work_item) }
+      let(:service_execute) { subject }
 
       let(:supported_widgets) do
         [
@@ -43,5 +45,47 @@
         ]
       end
     end
+
+    context 'when updating widgets' do
+      context 'for the weight widget' do
+        let(:widget_params) { { weight_widget: { weight: new_weight } } }
+
+        before do
+          stub_licensed_features(issue_weights: true)
+
+          work_item.update!(weight: 1)
+        end
+
+        context 'when weight is changed' do
+          let(:new_weight) { nil }
+
+          it "triggers 'issuableWeightUpdated' for issuable weight update subscription" do
+            expect(GraphqlTriggers).to receive(:issuable_weight_updated).with(work_item).and_call_original
+
+            subject
+          end
+        end
+
+        context 'when weight remains unchanged' do
+          let(:new_weight) { 1 }
+
+          it "does not trigger 'issuableWeightUpdated' for issuable weight update subscription" do
+            expect(GraphqlTriggers).not_to receive(:issuable_weight_updated)
+
+            subject
+          end
+        end
+
+        context 'when weight widget param is not provided' do
+          let(:widget_params) {}
+
+          it "does not trigger 'issuableWeightUpdated' for issuable weight update subscription" do
+            expect(GraphqlTriggers).not_to receive(:issuable_weight_updated)
+
+            subject
+          end
+        end
+      end
+    end
   end
 end

spec/graphql/types/subscription_type_spec.rb

@@ -13,6 +13,6 @@
       merge_request_reviewers_updated
     ]
 
-    expect(described_class).to have_graphql_fields(*expected_fields).only
+    expect(described_class).to include_graphql_fields(*expected_fields)
   end
 end