Resolve "Changes will be lost if multiple people edit a wiki page"

app/controllers/concerns/wiki_actions.rb

@@ -115,9 +115,6 @@ module WikiActions
       @error = response.message
       render 'shared/wikis/edit'
     end
-  rescue WikiPage::PageChangedError, WikiPage::PageRenameError => e
-    @error = e.message
-    render 'shared/wikis/edit'
   end
   # rubocop:enable Gitlab/ModuleWithInstanceVariables
 

app/services/wiki_pages/update_service.rb

@@ -2,6 +2,8 @@
 
 module WikiPages
   class UpdateService < WikiPages::BaseService
+    UpdateError = Class.new(StandardError)
+
     def execute(page)
       # this class is not thread safe!
       @old_slug = page.slug
@@ -10,11 +12,15 @@ module WikiPages
         execute_hooks(page)
         ServiceResponse.success(payload: { page: page })
       else
-        ServiceResponse.error(
-          message: _('Could not update wiki page'),
-          payload: { page: page }
-        )
+        raise UpdateError, s_('Could not update wiki page')
       end
+    rescue UpdateError, WikiPage::PageChangedError, WikiPage::PageRenameError => e
+      page.update_attributes(@params) # rubocop:disable Rails/ActiveRecordAliases
+
+      ServiceResponse.error(
+        message: e.message,
+        payload: { page: page }
+      )
     end
 
     def usage_counter_action

changelogs/unreleased/200002-changes-will-be-lost-if-multiple-people-edit-a-wiki-page.yml

+---
+title: Preserve user changes in the wiki editor if multiple people edit the page
+merge_request: 61120
+author:
+type: fixed

spec/support/shared_examples/features/wiki/user_updates_wiki_page_shared_examples.rb

@@ -117,14 +117,6 @@ RSpec.shared_examples 'User updates wiki page' do
       expect(page).to have_selector('.atwho-view')
     end
 
-    it 'shows the error message', :js do
-      wiki_page.update(content: 'Update') # rubocop:disable Rails/SaveBang
-
-      click_button('Save changes')
-
-      expect(page).to have_content('Someone edited the page the same time you did.')
-    end
-
     it 'updates a page', :js do
       fill_in('Content', with: 'Updated Wiki Content')
       click_on('Save changes')
@@ -145,6 +137,18 @@ RSpec.shared_examples 'User updates wiki page' do
     end
 
     it_behaves_like 'wiki file attachments'
+
+    context 'when multiple people edit the page at the same time' do
+      it 'preserves user changes in the wiki editor', :js do
+        wiki_page.update(content: 'Some Other Updates') # rubocop:disable Rails/SaveBang
+
+        fill_in('Content', with: 'Updated Wiki Content')
+        click_on('Save changes')
+
+        expect(page).to have_content('Someone edited the page the same time you did.')
+        expect(find('textarea#wiki_content').value).to eq('Updated Wiki Content')
+      end
+    end
   end
 
   context 'when the page is in a subdir', :js do