1 files changed, 100 insertions, 0 deletions
diff --git a/lib/gitlab/markdown/label_reference_filter.rb b/lib/gitlab/markdown/label_reference_filter.rb
new file mode 100644
index 00000000000..9753d0ac0f9
--- /dev/null
+++ b/lib/gitlab/markdown/label_reference_filter.rb
@@ -0,0 +1,100 @@
+require 'html/pipeline'
+
+module Gitlab
+  module Markdown
+    # HTML filter that replaces label references with links. References within
+    # <pre>, <code>, <a>, and <style> elements are ignored.
+    #
+    # Context options:
+    #   :project (required) - Current project.
+    #   :reference_class    - Custom CSS class added to reference links.
+    #   :only_path          - Generate path-only links.
+    #
+    class LabelReferenceFilter < HTML::Pipeline::Filter
+      # Public: Find label references in text
+      #
+      #   LabelReferenceFilter.references_in(text) do |match, label|
+      #     "<a href=...>#{label}</a>"
+      #   end
+      #
+      # text - String text to search.
+      #
+      # Yields the String match and the Integer label ID.
+      #
+      # Returns a String replaced with the return of the block.
+      def self.references_in(text)
+        text.gsub(LABEL_PATTERN) do |match|
+          yield match, $~[:label].to_i
+        end
+      end
+
+      # Pattern used to extract label references from text
+      #
+      # This pattern supports cross-project references.
+      LABEL_PATTERN = /~(?<label>\d+)/
+
+      # Don't look for references in text nodes that are children of these
+      # elements.
+      IGNORE_PARENTS = %w(pre code a style).to_set
+
+      def call
+        doc.search('text()').each do |node|
+          content = node.to_html
+
+          next if project.nil?
+          next unless content.match(LABEL_PATTERN)
+          next if has_ancestor?(node, IGNORE_PARENTS)
+
+          html = label_link_filter(content)
+
+          next if html == content
+
+          node.replace(html)
+        end
+
+        doc
+      end
+
+      def validate
+        needs :project
+      end
+
+      # Replace label references in text with links to the label specified.
+      #
+      # text - String text to replace references in.
+      #
+      # Returns a String with label references replaced with links. All links
+      # have `gfm` and `gfm-label` class names attached for styling.
+      def label_link_filter(text)
+        project = context[:project]
+
+        self.class.references_in(text) do |match, id|
+          if label = project.labels.find_by(id: id)
+            url = url_for_label(project, label)
+
+            klass = "gfm gfm-label #{context[:reference_class]}".strip
+
+            %(<a href="#{url}" class="#{klass}">#{render_colored_label(label)}</a>)
+          else
+            match
+          end
+        end
+      end
+
+      def url_for_label(project, label)
+        h = Rails.application.routes.url_helpers
+        h.namespace_project_issues_path(project.namespace, project,
+                                        label_name: label.name,
+                                        only_path: context[:only_path])
+      end
+
+      def render_colored_label(label)
+        LabelsHelper.render_colored_label(label)
+      end
+
+      def project
+        context[:project]
+      end
+    end
+  end
+end