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.

1 files changed, 21 insertions, 9 deletions

diff --git a/app/helpers/gitlab_markdown_helper.rb b/app/helpers/gitlab_markdown_helper.rb
index 1a259656f31..d24680b8617 100644
--- a/app/helpers/gitlab_markdown_helper.rb
+++ b/app/helpers/gitlab_markdown_helper.rb
@@ -51,17 +51,15 @@ module GitlabMarkdownHelper
     context[:project] ||= @project
 
     html = Banzai.render(text, context)
+    banzai_postprocess(html, context)
+  end
 
-    context.merge!(
-      current_user:   (current_user if defined?(current_user)),
+  def markdown_field(object, field)
+    object = object.for_display if object.respond_to?(:for_display)
+    return "" unless object.present?
 
-      # RelativeLinkFilter
-      requested_path: @path,
-      project_wiki:   @project_wiki,
-      ref:            @ref
-    )
-
-    Banzai.post_process(html, context)
+    html = Banzai.render_field(object, field)
+    banzai_postprocess(html, object.banzai_render_context(field))
   end
 
   def asciidoc(text)
@@ -196,4 +194,18 @@ module GitlabMarkdownHelper
       icon(options[:icon])
     end
   end
+
+  # Calls Banzai.post_process with some common context options
+  def banzai_postprocess(html, context)
+    context.merge!(
+      current_user:   (current_user if defined?(current_user)),
+
+      # RelativeLinkFilter
+      requested_path: @path,
+      project_wiki:   @project_wiki,
+      ref:            @ref
+    )
+
+    Banzai.post_process(html, context)
+  end
 end