link issuable reference to itself in header

app/helpers/issuables_helper.rb

 module IssuablesHelper
+  include GitlabRoutingHelper
+
   def sidebar_gutter_toggle_icon
     sidebar_gutter_collapsed? ? icon('angle-double-left', { 'aria-hidden': 'true' }) : icon('angle-double-right', { 'aria-hidden': 'true' })
   end
@@ -95,8 +97,23 @@ module IssuablesHelper
     h(milestone_title.presence || default_label)
   end
 
+  def to_url_reference(issuable)
+    case issuable
+    when Issue
+      link_to issuable.to_reference, issue_url(issuable)
+    when MergeRequest
+      link_to issuable.to_reference, merge_request_url(issuable)
+    else
+      issuable.to_reference
+    end
+  end
+
   def issuable_meta(issuable, project, text)
-    output = content_tag :strong, "#{text} #{issuable.to_reference}", class: "identifier"
+    output = content_tag(:strong, class: "identifier") do
+      concat("#{text} ")
+      concat(to_url_reference(issuable))
+    end
+
     output << " opened #{time_ago_with_tooltip(issuable.created_at)} by ".html_safe
     output << content_tag(:strong) do
       author_output = link_to_member(project, issuable.author, size: 24, mobile_classes: "hidden-xs", tooltip: true)

changelogs/unreleased/24137-issuable-permalink.yml

+---
+title: Link issuable reference to itself in meta-header
+merge_request: 9641
+author: mhasbini

spec/features/issues/form_spec.rb

 require 'rails_helper'
 
 describe 'New/edit issue', feature: true, js: true do
+  include GitlabRoutingHelper
+
   let!(:project)   { create(:project) }
   let!(:user)      { create(:user)}
   let!(:user2)     { create(:user)}
@@ -78,6 +80,14 @@ describe 'New/edit issue', feature: true, js: true do
           expect(page).to have_content label2.title
         end
       end
+
+      page.within '.issuable-meta' do
+        issue = Issue.find_by(title: 'title')
+
+        expect(page).to have_text("Issue #{issue.to_reference}")
+        # compare paths because the host differ in test
+        expect(find_link(issue.to_reference)[:href]).to end_with(issue_path(issue))
+      end
     end
 
     it 'correctly updates the dropdown toggle when removing a label' do

spec/features/merge_requests/form_spec.rb

 require 'rails_helper'
 
 describe 'New/edit merge request', feature: true, js: true do
+  include GitlabRoutingHelper
+
   let!(:project)   { create(:project, visibility_level: Gitlab::VisibilityLevel::PUBLIC) }
   let(:fork_project) { create(:project, forked_from_project: project) }
   let!(:user)      { create(:user)}
@@ -84,6 +86,15 @@ describe 'New/edit merge request', feature: true, js: true do
             expect(page).to have_content label2.title
           end
         end
+
+        page.within '.issuable-meta' do
+          merge_request = MergeRequest.find_by(source_branch: 'fix')
+
+          expect(page).to have_text("Merge Request #{merge_request.to_reference}")
+          # compare paths because the host differ in test
+          expect(find_link(merge_request.to_reference)[:href])
+            .to end_with(merge_request_path(merge_request))
+        end
       end
     end