Add the proper empty state when wiki page not found

Changelog: changed

app/controllers/concerns/wiki_actions.rb

@@ -157,6 +157,8 @@ def handle_redirection
       )
     elsif show_create_form?
       handle_create_form
+    elsif wiki.exists?
+      render 'shared/wikis/404', status: :not_found
     else
       render 'shared/wikis/empty'
     end

app/views/shared/wikis/404.html.haml

+- page_title _("Wiki")
+- @right_sidebar = true
+- add_page_specific_style 'page_bundles/wiki'
+
+- if @error.present?
+  = render Pajamas::AlertComponent.new(alert_options: { id: 'error_explanation', class: 'gl-mb-3'},
+    dismissible: false,
+    variant: :danger) do |c|
+    - c.with_body do
+      %ul.gl-pl-4
+        = @error
+
+= render Pajamas::EmptyStateComponent.new(svg_path: 'illustrations/empty-state/empty-wiki-md.svg',
+  title: _('Sorry, this page doesn\'t exist'),
+  empty_state_options: { data: { testid: 'wiki-404' } }) do |c|
+
+  - c.with_description do
+    = s_('Wiki|Use the sidebar to find a different page.')
+
+= render 'shared/wikis/sidebar'

locale/gitlab.pot

@@ -50588,6 +50588,9 @@ msgstr ""
 msgid "Sorry, no projects matched your search"
 msgstr ""
+msgid "Sorry, this page doesn't exist"
+msgstr ""
+
 msgid "Sorry, you have exceeded the maximum browsable page number. Please use the API to explore further."
 msgstr ""
@@ -59604,6 +59607,9 @@ msgstr ""
 msgid "Wiki|There are no pages in this wiki yet"
 msgstr ""
+msgid "Wiki|Use the sidebar to find a different page."
+msgstr ""
+
 msgid "Wiki|View all pages"
 msgstr ""

spec/support/shared_examples/controllers/wiki_actions_shared_examples.rb

@@ -255,8 +255,8 @@
         it 'shows the empty state' do
           request
 
-          expect(response).to have_gitlab_http_status(:ok)
-          expect(response).to render_template('shared/wikis/empty')
+          expect(response).to have_gitlab_http_status(:not_found)
+          expect(response).to render_template('shared/wikis/404')
         end
       end
     end