Merge branch 'banzai-issue-filter-queries' into 'master'

Reduce SQL query counts in IssueReferenceFilter

## What does this MR do?

This MR adds a preparation phase for reference filters that allows them to prepare/create data structures used while iterating over HTML nodes. In this particular case the preparation phase is used for issue references to greatly cut down the amount of queries executed to get projects/issues for Markdown references.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

Rendering Markdown containing issue references would run at most two queries for every issue reference: one to get the project and one to get the issue from said project. When rendering Markdown with lots of issue references this would result in _a lot_ of queries being executed.

## What are the relevant issue numbers?

#18042

See merge request !4410

2 files changed, 58 insertions, 3 deletions

diff --git a/spec/lib/banzai/filter/abstract_link_filter_spec.rb b/spec/lib/banzai/filter/abstract_link_filter_spec.rb
new file mode 100644
index 00000000000..0c55d8e19da
--- /dev/null
+++ b/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
diff --git a/spec/lib/banzai/filter/issue_reference_filter_spec.rb b/spec/lib/banzai/filter/issue_reference_filter_spec.rb
index 8e6a264970d..25f0bc2092f 100644
--- a/spec/lib/banzai/filter/issue_reference_filter_spec.rb
+++ b/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