Add support for `twitter:label` meta tags

app/helpers/page_layout_helper.rb

@@ -58,6 +58,30 @@ module PageLayoutHelper
     end
   end
 
+  # Define or get attributes to be used as Twitter card metadata
+  #
+  # map - Hash of label => data pairs. Keys become labels, values become data
+  #
+  # Raises ArgumentError if given more than two attributes
+  def page_card_attributes(map = {})
+    raise ArgumentError, 'cannot provide more than two attributes' if map.length > 2
+
+    @page_card_attributes ||= {}
+    @page_card_attributes = map.reject { |_,v| v.blank? } if map.present?
+    @page_card_attributes
+  end
+
+  def page_card_meta_tags
+    tags = ''
+
+    page_card_attributes.each_with_index do |pair, i|
+      tags << tag(:meta, property: "twitter:label#{i + 1}", content: pair[0])
+      tags << tag(:meta, property: "twitter:data#{i + 1}",  content: pair[1])
+    end
+
+    tags.html_safe
+  end
+
   def header_title(title = nil, title_url = nil)
     if title
       @header_title     = title

app/models/concerns/issuable.rb

@@ -161,6 +161,14 @@ module Issuable
     self.class.to_s.underscore
   end
 
+  # Returns a Hash of attributes to be used for Twitter card metadata
+  def card_attributes
+    {
+      'Author'   => author.try(:name),
+      'Assignee' => assignee.try(:name)
+    }
+  end
+
   def notes_with_associations
     notes.includes(:author, :project)
   end

app/views/layouts/_head.html.haml

@@ -12,6 +12,7 @@
   %meta{property: 'og:description', content: page_description}
   %meta{property: 'og:image',       content: page_image}
   %meta{property: 'og:url',         content: request.base_url + request.fullpath}
+  = page_card_meta_tags
 
   %title= page_title
 

app/views/projects/issues/show.html.haml

 - page_title           "#{@issue.title} (##{@issue.iid})", "Issues"
 - page_description     @issue.description
+- page_card_attributes @issue.card_attributes
 
 = render "header_title"
 

app/views/projects/merge_requests/_show.html.haml

 - page_title           "#{@merge_request.title} (##{@merge_request.iid})", "Merge Requests"
 - page_description     @merge_request.description
+- page_card_attributes @merge_request.card_attributes
 
 = render "header_title"
 

spec/helpers/page_layout_helper_spec.rb

@@ -97,4 +97,33 @@ describe PageLayoutHelper do
       end
     end
   end
+
+  describe 'page_card_attributes' do
+    it 'raises ArgumentError when given more than two attributes' do
+      map = { foo: 'foo', bar: 'bar', baz: 'baz' }
+
+      expect { helper.page_card_attributes(map) }.
+        to raise_error(ArgumentError, /more than two attributes/)
+    end
+
+    it 'rejects blank values' do
+      map = { foo: 'foo', bar: '' }
+      helper.page_card_attributes(map)
+
+      expect(helper.page_card_attributes).to eq({ foo: 'foo' })
+    end
+  end
+
+  describe 'page_card_meta_tags' do
+    it 'returns the twitter:label and twitter:data tags' do
+      allow(helper).to receive(:page_card_attributes).and_return(foo: 'bar')
+
+      tags = helper.page_card_meta_tags
+
+      aggregate_failures do
+        expect(tags).to include %q(<meta property="twitter:label1" content="foo" />)
+        expect(tags).to include %q(<meta property="twitter:data1" content="bar" />)
+      end
+    end
+  end
 end

spec/models/concerns/issuable_spec.rb

@@ -81,4 +81,22 @@ describe Issue, "Issuable" do
       expect(hook_data[:object_attributes]).to eq(issue.hook_attrs)
     end
   end
+
+  describe '#card_attributes' do
+    it 'includes the author name' do
+      allow(issue).to receive(:author).and_return(double(name: 'Robert'))
+      allow(issue).to receive(:assignee).and_return(nil)
+
+      expect(issue.card_attributes).
+        to eq({'Author' => 'Robert', 'Assignee' => nil})
+    end
+
+    it 'includes the assignee name' do
+      allow(issue).to receive(:author).and_return(double(name: 'Robert'))
+      allow(issue).to receive(:assignee).and_return(double(name: 'Douwe'))
+
+      expect(issue.card_attributes).
+        to eq({'Author' => 'Robert', 'Assignee' => 'Douwe'})
+    end
+  end
 end