Reduce queries in IssueReferenceFilter

This reduces the number of queries executed in IssueReferenceFilter by
retrieving the various projects/issues that may be referenced in batches
_before_ iterating over all the HTML nodes.

A chunk of the logic resides in AbstractReferenceFilter so it can be
re-used by other filters in the future.

lib/banzai/filter/abstract_reference_filter.rb

@@ -103,7 +103,7 @@ module Banzai
         ref_pattern = object_class.reference_pattern
         link_pattern = object_class.link_reference_pattern
 
-        each_node do |node|
+        nodes.each do |node|
           if text_node?(node) && ref_pattern
             replace_text_when_pattern_matches(node, ref_pattern) do |content|
               object_link_filter(content, ref_pattern)
@@ -206,6 +206,55 @@ module Banzai
         text
       end
 
+      # Returns a Hash containing all object references (e.g. issue IDs) per the
+      # project they belong to.
+      def references_per_project
+        @references_per_project ||= begin
+          refs = Hash.new { |hash, key| hash[key] = Set.new }
+
+          regex = Regexp.union(object_class.reference_pattern,
+                               object_class.link_reference_pattern)
+
+          nodes.each do |node|
+            node.to_html.scan(regex) do
+              project = $~[:project] || current_project_path
+
+              refs[project] << $~[object_sym]
+            end
+          end
+
+          refs
+        end
+      end
+
+      # Returns a Hash containing referenced projects grouped per their full
+      # path.
+      def projects_per_reference
+        @projects_per_reference ||= begin
+          hash = {}
+          refs = Set.new
+
+          references_per_project.each do |project_ref, _|
+            refs << project_ref
+          end
+
+          find_projects_for_paths(refs.to_a).each do |project|
+            hash[project.path_with_namespace] = project
+          end
+
+          hash
+        end
+      end
+
+      # Returns the projects for the given paths.
+      def find_projects_for_paths(paths)
+        Project.where_paths_in(paths).includes(:namespace)
+      end
+
+      def current_project_path
+        @current_project_path ||= project.path_with_namespace
+      end
+
       private
 
       def project_refs_cache

lib/banzai/filter/issue_reference_filter.rb

@@ -11,13 +11,40 @@ module Banzai
         Issue
       end
 
-      def find_object(project, id)
-        project.get_issue(id)
+      def find_object(project, iid)
+        issues_per_project[project][iid]
       end
 
       def url_for_object(issue, project)
         IssuesHelper.url_for_issue(issue.iid, project, only_path: context[:only_path])
       end
+
+      def project_from_ref(ref)
+        projects_per_reference[ref || current_project_path]
+      end
+
+      # Returns a Hash containing the issues per Project instance.
+      def issues_per_project
+        @issues_per_project ||= begin
+          hash = Hash.new { |h, k| h[k] = {} }
+
+          projects_per_reference.each do |path, project|
+            issue_ids = references_per_project[path]
+
+            next unless project.default_issues_tracker?
+
+            project.issues.where(iid: issue_ids.to_a).each do |issue|
+              hash[project][issue.iid] = issue
+            end
+          end
+
+          hash
+        end
+      end
+
+      def find_projects_for_paths(paths)
+        super(paths).includes(:gitlab_issue_tracker_service)
+      end
     end
   end
 end

spec/lib/banzai/filter/abstract_link_filter_spec.rb

@@ -0,0 +1,52 @@
+require 'spec_helper'
+
+describe Banzai::Filter::AbstractReferenceFilter do
+  let(:project) { create(:empty_project) }
+
+  describe '#references_per_project' do
+    it 'returns a Hash containing references grouped per project paths' do
+      doc = Nokogiri::HTML.fragment("#1 #{project.to_reference}#2")
+      filter = described_class.new(doc, project: project)
+
+      expect(filter).to receive(:object_class).twice.and_return(Issue)
+      expect(filter).to receive(:object_sym).twice.and_return(:issue)
+
+      refs = filter.references_per_project
+
+      expect(refs).to be_an_instance_of(Hash)
+      expect(refs[project.to_reference]).to eq(Set.new(%w[1 2]))
+    end
+  end
+
+  describe '#projects_per_reference' do
+    it 'returns a Hash containing projects grouped per project paths' do
+      doc = Nokogiri::HTML.fragment('')
+      filter = described_class.new(doc, project: project)
+
+      expect(filter).to receive(:references_per_project).
+        and_return({ project.path_with_namespace => Set.new(%w[1]) })
+
+      expect(filter.projects_per_reference).
+        to eq({ project.path_with_namespace => project })
+    end
+  end
+
+  describe '#find_projects_for_paths' do
+    it 'returns a list of Projects for a list of paths' do
+      doc = Nokogiri::HTML.fragment('')
+      filter = described_class.new(doc, project: project)
+
+      expect(filter.find_projects_for_paths([project.path_with_namespace])).
+        to eq([project])
+    end
+  end
+
+  describe '#current_project_path' do
+    it 'returns the path of the current project' do
+      doc = Nokogiri::HTML.fragment('')
+      filter = described_class.new(doc, project: project)
+
+      expect(filter.current_project_path).to eq(project.path_with_namespace)
+    end
+  end
+end

spec/lib/banzai/filter/issue_reference_filter_spec.rb

@@ -25,7 +25,9 @@ describe Banzai::Filter::IssueReferenceFilter, lib: true do
     let(:reference) { issue.to_reference }
 
     it 'ignores valid references when using non-default tracker' do
-      expect(project).to receive(:get_issue).with(issue.iid).and_return(nil)
+      expect_any_instance_of(described_class).to receive(:find_object).
+        with(project, issue.iid).
+        and_return(nil)
 
       exp = act = "Issue #{reference}"
       expect(reference_filter(act).to_html).to eq exp
@@ -107,8 +109,9 @@ describe Banzai::Filter::IssueReferenceFilter, lib: true do
     let(:reference) { issue.to_reference(project) }
 
     it 'ignores valid references when cross-reference project uses external tracker' do
-      expect_any_instance_of(Project).to receive(:get_issue).
-        with(issue.iid).and_return(nil)
+      expect_any_instance_of(described_class).to receive(:find_object).
+        with(project2, issue.iid).
+        and_return(nil)
 
       exp = act = "Issue #{reference}"
       expect(reference_filter(act).to_html).to eq exp

spec/services/git_push_service_spec.rb

@@ -312,7 +312,8 @@ describe GitPushService, services: true do
       end
 
       it "doesn't close issues when external issue tracker is in use" do
-        allow(project).to receive(:default_issues_tracker?).and_return(false)
+        allow_any_instance_of(Project).to receive(:default_issues_tracker?).
+          and_return(false)
 
         # The push still shouldn't create cross-reference notes.
         expect do