Add markdown cache columns to the database, but don't use them yet

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

2 files changed, 76 insertions, 1 deletions

diff --git a/spec/lib/banzai/renderer_spec.rb b/spec/lib/banzai/renderer_spec.rb
new file mode 100644
index 00000000000..aaa6b12e67e
--- /dev/null
+++ b/spec/lib/banzai/renderer_spec.rb
@@ -0,0 +1,74 @@
+require 'spec_helper'
+
+describe Banzai::Renderer do
+  def expect_render(project = :project)
+    expected_context = { project: project }
+    expect(renderer).to receive(:cacheless_render) { :html }.with(:markdown, expected_context)
+  end
+
+  def expect_cache_update
+    expect(object).to receive(:update_column).with("field_html", :html)
+  end
+
+  def fake_object(*features)
+    markdown = :markdown if features.include?(:markdown)
+    html = :html if features.include?(:html)
+
+    object = double(
+      "object",
+      banzai_render_context: { project: :project },
+      field: markdown,
+      field_html: html
+    )
+
+    allow(object).to receive(:markdown_cache_field_for).with(:field).and_return("field_html")
+    allow(object).to receive(:new_record?).and_return(features.include?(:new))
+    allow(object).to receive(:destroyed?).and_return(features.include?(:destroyed))
+
+    object
+  end
+
+  describe "#render_field" do
+    let(:renderer) { Banzai::Renderer }
+    let(:subject) { renderer.render_field(object, :field) }
+
+    context "with an empty cache" do
+      let(:object) { fake_object(:markdown) }
+      it "caches and returns the result" do
+        expect_render
+        expect_cache_update
+        expect(subject).to eq(:html)
+      end
+    end
+
+    context "with a filled cache" do
+      let(:object) { fake_object(:markdown, :html) }
+
+      it "uses the cache" do
+        expect_render.never
+        expect_cache_update.never
+        should eq(:html)
+      end
+    end
+
+    context "new object" do
+      let(:object) { fake_object(:new, :markdown) }
+
+      it "doesn't cache the result" do
+        expect_render
+        expect_cache_update.never
+        expect(subject).to eq(:html)
+      end
+    end
+
+    context "destroyed object" do
+      let(:object) { fake_object(:destroyed, :markdown) }
+
+      it "doesn't cache the result" do
+        expect_render
+        expect_cache_update.never
+        expect(subject).to eq(:html)
+      end
+    end
+  end
+end
diff --git a/spec/lib/gitlab/import_export/attribute_configuration_spec.rb b/spec/lib/gitlab/import_export/attribute_configuration_spec.rb
index 2e19d590d83..ea65a5dfed1 100644
--- a/spec/lib/gitlab/import_export/attribute_configuration_spec.rb
+++ b/spec/lib/gitlab/import_export/attribute_configuration_spec.rb
@@ -26,10 +26,11 @@ describe 'Import/Export attribute configuration', lib: true do
   it 'has no new columns' do
     relation_names.each do |relation_name|
       relation_class = relation_class_for_name(relation_name)
+      relation_attributes = relation_class.new.attributes.keys
 
       expect(safe_model_attributes[relation_class.to_s]).not_to be_nil, "Expected exported class #{relation_class} to exist in safe_model_attributes"
 
-      current_attributes = parsed_attributes(relation_name, relation_class.attribute_names)
+      current_attributes = parsed_attributes(relation_name, relation_attributes)
       safe_attributes = safe_model_attributes[relation_class.to_s]
       new_attributes = current_attributes - safe_attributes