Add blocked by issues count on issues metadata

Backend part of showing blocked by issues count on issues list.

app/views/shared/_issuable_meta_data.html.haml

@@ -2,7 +2,7 @@
 - issue_votes        = @issuable_meta_data[issuable.id]
 - upvotes, downvotes = issue_votes.upvotes, issue_votes.downvotes
 - issuable_path      = issuable_path(issuable, anchor: 'notes')
-- issuable_mr        = @issuable_meta_data[issuable.id].merge_requests_count(current_user)
+- issuable_mr        = @issuable_meta_data[issuable.id].merge_requests_count
 
 - if issuable_mr > 0
   %li.issuable-mr.d-none.d-sm-block.has-tooltip{ title: _('Related merge requests') }

ee/app/models/issue_link.rb

@@ -65,6 +65,23 @@ class IssueLink < ApplicationRecord
         .joins("INNER JOIN issues ON issues.id = issue_links.#{blocking_key}")
         .where('issues.state_id' => Issuable::STATE_ID_MAP[:opened])
     end
+
+    def blocking_issues_for_collection(issues_ids)
+      from_union([
+        select('COUNT(*), issue_links.source_id AS blocking_issue_id')
+          .joins(:target)
+          .where(issues: { state_id: Issue.available_states[:opened] })
+          .where(link_type: TYPE_BLOCKS)
+          .where(source_id: issues_ids)
+          .group(:blocking_issue_id),
+        select('COUNT(*), issue_links.target_id AS blocking_issue_id')
+          .joins(:source)
+          .where(issues: { state_id: Issue.available_states[:opened] })
+          .where(link_type: TYPE_IS_BLOCKED_BY)
+          .where(target_id: issues_ids)
+          .group(:blocking_issue_id)
+      ], remove_duplicates: false).select('blocking_issue_id, SUM(count) AS count').group('blocking_issue_id')
+    end
   end
 
   def check_self_relation

ee/lib/ee/gitlab/issuable_metadata.rb

+# frozen_string_literal: true
+
+module EE
+  module Gitlab
+    module IssuableMetadata
+      extend ::Gitlab::Utils::Override
+
+      override :metadata_for_issuable
+      def metadata_for_issuable(id)
+        return super unless ::Feature.enabled?(:blocking_issues_counts)
+
+        super.tap do |data|
+          blocking_count =
+            grouped_blocking_issues_count.find do |issue_link|
+              issue_link.blocking_issue_id == id
+            end
+
+          data.blocking_issues_count = blocking_count.try(:count).to_i
+        end
+      end
+
+      def grouped_blocking_issues_count
+        strong_memoize(:grouped_blocking_issues_count) do
+          next IssueLink.none unless collection_type == 'Issue'
+
+          IssueLink.blocking_issues_for_collection(issuable_ids)
+        end
+      end
+    end
+  end
+end

ee/spec/lib/ee/gitlab/issuable_metadata_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::IssuableMetadata do
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project1) { create(:project, :public, :repository, creator: user, namespace: user.namespace) }
+  let_it_be(:project2) { create(:project, :public, :repository, creator: user, namespace: user.namespace) }
+
+  context 'issues' do
+    # blocked issues
+    let_it_be(:blocked_issue_1) { create(:issue, author: user, project: project1) }
+    let_it_be(:blocked_issue_2) { create(:issue, author: user, project: project2) }
+    let_it_be(:blocked_issue_3) { create(:issue, author: user, project: project1) }
+    let_it_be(:closed_blocked_issue) { create(:issue, author: user, project: project2, state: :closed) }
+    # blocking issues (as target or source)
+    let_it_be(:blocking_issue_1) { create(:issue, project: project1) }
+    let_it_be(:blocking_issue_2) { create(:issue, project: project2) }
+
+    before_all do
+      create(:issue_link, source: blocking_issue_1, target: blocked_issue_1, link_type: IssueLink::TYPE_BLOCKS)
+      create(:issue_link, source: blocking_issue_2, target: blocked_issue_2, link_type: IssueLink::TYPE_BLOCKS)
+      create(:issue_link, source: blocking_issue_1, target: closed_blocked_issue, link_type: IssueLink::TYPE_BLOCKS)
+      create(:issue_link, source: blocked_issue_3, target: blocking_issue_1, link_type: IssueLink::TYPE_IS_BLOCKED_BY)
+    end
+
+    it 'aggregates stats on issues' do
+      data = described_class.new(user, Issue.all.limit(6)).data # rubocop: disable CodeReuse/ActiveRecord
+
+      expect(data.count).to eq(6)
+      expect(data[blocking_issue_1.id].blocking_issues_count).to eq(2)
+      expect(data[blocking_issue_2.id].blocking_issues_count).to eq(1)
+      expect(data[blocked_issue_1.id].blocking_issues_count).to eq(0)
+    end
+
+    context 'when blocking_issues_counts feature flag is disabled' do
+      before do
+        stub_feature_flags(blocking_issues_counts: false)
+      end
+
+      it 'does not return blocking_issues_counts' do
+        create(:award_emoji, :upvote, awardable: blocking_issue_1)
+
+        meta_data = described_class.new(user, Issue.all.limit(7)).data # rubocop: disable CodeReuse/ActiveRecord
+
+        expect(meta_data.values.map { |value| value.blocking_issues_count }.uniq).to eq([nil])
+        # Make sure other properties are still being fetched
+        expect(meta_data[blocking_issue_1.id].upvotes).to eq(1)
+      end
+    end
+  end
+end

ee/spec/models/issue_link_spec.rb

@@ -84,4 +84,22 @@ RSpec.describe IssueLink do
       expect(described_class.inverse_link_type('is_blocked_by')).to eq 'blocks'
     end
   end
+
+  describe '.blocking_issues_for_collection' do
+    it 'returns blocking issues count grouped by issue id' do
+      issue_1 = create(:issue)
+      issue_2 = create(:issue)
+      issue_3 = create(:issue)
+      blocking_issue_1 = create(:issue, project: issue_1.project)
+      blocking_issue_2 = create(:issue, project: issue_2.project)
+      create(:issue_link, source: blocking_issue_1, target: issue_1, link_type: IssueLink::TYPE_BLOCKS)
+      create(:issue_link, source: issue_2, target: blocking_issue_1, link_type: IssueLink::TYPE_IS_BLOCKED_BY)
+      create(:issue_link, source: blocking_issue_2, target: issue_3, link_type: IssueLink::TYPE_BLOCKS)
+
+      results = described_class.blocking_issues_for_collection([blocking_issue_1, blocking_issue_2])
+
+      expect(results.find { |link| link.blocking_issue_id == blocking_issue_1.id }.count).to eq(2)
+      expect(results.find { |link| link.blocking_issue_id == blocking_issue_2.id }.count).to eq(1)
+    end
+  end
 end

lib/api/entities/issuable_entity.rb

@@ -11,7 +11,12 @@ module API
       # Avoids an N+1 query when metadata is included
       def issuable_metadata(subject, options, method, args = nil)
         cached_subject = options.dig(:issuable_metadata, subject.id)
-        (cached_subject || subject).public_send(method, *args) # rubocop: disable GitlabSecurity/PublicSend
+
+        if cached_subject
+          cached_subject[method]
+        else
+          subject.public_send(method, *args) # rubocop: disable GitlabSecurity/PublicSend
+        end
       end
     end
   end

lib/gitlab/issuable_metadata.rb

@@ -7,11 +7,13 @@ module Gitlab
     # data structure to store issuable meta data like
     # upvotes, downvotes, notes and closing merge requests counts for issues and merge requests
     # this avoiding n+1 queries when loading issuable collections on frontend
-    IssuableMeta = Struct.new(:upvotes, :downvotes, :user_notes_count, :mrs_count) do
-      def merge_requests_count(user = nil)
-        mrs_count
-      end
-    end
+    IssuableMeta = Struct.new(
+      :upvotes,
+      :downvotes,
+      :user_notes_count,
+      :merge_requests_count,
+      :blocking_issues_count # EE-ONLY
+    )
 
     attr_reader :current_user, :issuable_collection
 
@@ -95,3 +97,5 @@ module Gitlab
     end
   end
 end
+
+Gitlab::IssuableMetadata.prepend_if_ee('EE::Gitlab::IssuableMetadata')