Prepopulate new issue with link to the parent

At the top of each issue detail view, there's a "New issue" link in the
dropdown menu.  Modify that link to prepopulate the newly-created issue
with a link to the original issue, to make it easier to create
interconnected issues without having to copy-paste or memorize the
parent issue id.

Changelog: changed

app/helpers/issues_helper.rb

@@ -174,7 +174,11 @@ module IssuesHelper
   end
 
   def issue_header_actions_data(project, issuable, current_user)
-    new_issuable_params = ({ issuable_template: 'incident', issue: { issue_type: 'incident' } } if issuable.incident?)
+    new_issuable_params = { issue: { description: _('Related to #%{issue_id}.') % { issue_id: issuable.iid } + "\n\n" } }
+    if issuable.incident?
+      new_issuable_params[:issuable_template] = 'incident'
+      new_issuable_params[:issue][:issue_type] = 'incident'
+    end
 
     {
       can_create_issue: show_new_issue_link?(project).to_s,

locale/gitlab.pot

@@ -27647,6 +27647,9 @@ msgstr ""
 msgid "Related merge requests"
 msgstr ""
 
+msgid "Related to #%{issue_id}."
+msgstr ""
+
 msgid "Relates to"
 msgstr ""
 

spec/features/incidents/user_views_incident_spec.rb

@@ -25,7 +25,7 @@ RSpec.describe "User views incident" do
   it 'shows the merge request and incident actions', :js, :aggregate_failures do
     click_button 'Incident actions'
 
-    expect(page).to have_link('New incident', href: new_project_issue_path(project, { issuable_template: 'incident', issue: { issue_type: 'incident' } }))
+    expect(page).to have_link('New incident', href: new_project_issue_path(project, { issuable_template: 'incident', issue: { issue_type: 'incident', description: "Related to \##{incident.iid}.\n\n" } }))
     expect(page).to have_button('Create merge request')
     expect(page).to have_button('Close incident')
   end

spec/features/issues/user_views_issue_spec.rb

@@ -25,7 +25,7 @@ RSpec.describe "User views issue" do
   it 'shows the merge request and issue actions', :js, :aggregate_failures do
     click_button 'Issue actions'
 
-    expect(page).to have_link('New issue', href: new_project_issue_path(project))
+    expect(page).to have_link('New issue', href: new_project_issue_path(project, { issue: { description: "Related to \##{issue.iid}.\n\n" } }))
     expect(page).to have_button('Create merge request')
     expect(page).to have_button('Close issue')
   end

spec/helpers/issues_helper_spec.rb

@@ -284,7 +284,7 @@ RSpec.describe IssuesHelper do
         iid: issue.iid,
         is_issue_author: 'false',
         issue_type: 'issue',
-        new_issue_path: new_project_issue_path(project),
+        new_issue_path: new_project_issue_path(project, { issue: { description: "Related to \##{issue.iid}.\n\n" } }),
         project_path: project.full_path,
         report_abuse_path: new_abuse_report_path(user_id: issue.author.id, ref_url: issue_url(issue)),
         submit_as_spam_path: mark_as_spam_project_issue_path(project, issue)