Fix error when trying to create a wiki page

Closes #15527.
Signed-off-by: Rémy Coutable <remy@rymai.me>

CHANGELOG

@@ -15,8 +15,9 @@ v 8.8.0 (unreleased)
   - Files over 5MB can only be viewed in their raw form, files over 1MB without highlighting !3718
   - Add support for supressing text diffs using .gitattributes on the default branch (Matt Oakes)
 
-v 8.7.2
+v 8.7.2 (unreleased)
   - The "New Branch" button is now loaded asynchronously
+  - Fix error 500 when trying to create a wiki page
 
 v 8.7.1
   - Throttle the update of `project.last_activity_at` to 1 minute. !3848

app/controllers/projects/wikis_controller.rb

@@ -40,10 +40,10 @@ class Projects::WikisController < Projects::ApplicationController
   end
 
   def update
-    @page = @project_wiki.find_page(params[:id])
-
     return render('empty') unless can?(current_user, :create_wiki, @project)
 
+    @page = @project_wiki.find_page(params[:id])
+
     if @page = WikiPages::UpdateService.new(@project, current_user, wiki_params).execute(@page)
       redirect_to(
         namespace_project_wiki_path(@project.namespace, @project, @page),

app/services/wiki_pages/create_service.rb

 module WikiPages
   class CreateService < WikiPages::BaseService
     def execute
-      page = WikiPage.new(@project.wiki)
+      project_wiki = ProjectWiki.new(@project, current_user)
+      page = WikiPage.new(project_wiki)
 
       if page.create(@params)
         execute_hooks(page, 'create')

spec/features/projects/wiki/user_creates_wiki_page_spec.rb

+require 'spec_helper'
+
+feature 'Projects > Wiki > User creates wiki page', feature: true do
+  let(:user) { create(:user) }
+
+  background do
+    project.team << [user, :master]
+    login_as(user)
+
+    visit namespace_project_path(project.namespace, project)
+    click_link 'Wiki'
+  end
+
+  context 'wiki project is in the user namespace' do
+    let(:project) { create(:project, namespace: user.namespace) }
+
+    context 'when wiki is empty' do
+      scenario 'user can create a new wiki page from the wiki home page' do
+        expect(page).to have_content('Home · Edit Page')
+
+        fill_in :wiki_content, with: 'My awesome wiki!'
+        click_button 'Create page'
+
+        expect(page).to have_content("Home · last edited by #{user.name}")
+        expect(page).to have_content('My awesome wiki!')
+      end
+    end
+
+    context 'when wiki is not empty' do
+      before do
+        WikiPages::CreateService.new(project, user, title: 'home', content: 'Home page').execute
+      end
+
+      scenario 'user can create a new wiki page', js: true do
+        click_link 'New Page'
+
+        fill_in :new_wiki_path, with: 'foo'
+        click_button 'Create Page'
+
+        expect(page).to have_content('Foo · Edit Page')
+
+        fill_in :wiki_content, with: 'My awesome wiki!'
+        click_button 'Create page'
+
+        expect(page).to have_content("Foo · last edited by #{user.name}")
+        expect(page).to have_content('My awesome wiki!')
+      end
+    end
+  end
+
+  context 'wiki project is in the user namespace' do
+    let(:project) { create(:project, namespace: create(:group, :public)) }
+
+    context 'when wiki is empty' do
+      scenario 'user can create a new wiki page from the wiki home page' do
+        expect(page).to have_content('Home · Edit Page')
+
+        fill_in :wiki_content, with: 'My awesome wiki!'
+        click_button 'Create page'
+
+        expect(page).to have_content("Home · last edited by #{user.name}")
+        expect(page).to have_content('My awesome wiki!')
+      end
+    end
+
+    context 'when wiki is not empty' do
+      before do
+        WikiPages::CreateService.new(project, user, title: 'home', content: 'Home page').execute
+      end
+
+      scenario 'user can create a new wiki page', js: true do
+        click_link 'New Page'
+
+        fill_in :new_wiki_path, with: 'foo'
+        click_button 'Create Page'
+
+        expect(page).to have_content('Foo · Edit Page')
+
+        fill_in :wiki_content, with: 'My awesome wiki!'
+        click_button 'Create page'
+
+        expect(page).to have_content("Foo · last edited by #{user.name}")
+        expect(page).to have_content('My awesome wiki!')
+      end
+    end
+  end
+end

spec/features/projects/wiki/user_updates_wiki_page_spec.rb

+require 'spec_helper'
+
+feature 'Projects > Wiki > User updates wiki page', feature: true do
+  let(:user) { create(:user) }
+
+  background do
+    project.team << [user, :master]
+    login_as(user)
+
+    visit namespace_project_path(project.namespace, project)
+    WikiPages::CreateService.new(project, user, title: 'home', content: 'Home page').execute
+    click_link 'Wiki'
+  end
+
+  context 'wiki project is in the user namespace' do
+    let(:project) { create(:project, namespace: user.namespace) }
+
+    scenario 'user can update the wiki home page' do
+      click_link 'Edit'
+
+      expect(page).to have_content('Home · Edit Page')
+
+      fill_in :wiki_content, with: 'My awesome wiki!'
+      click_button 'Save changes'
+
+      expect(page).to have_content("Home · last edited by #{user.name}")
+      expect(page).to have_content('My awesome wiki!')
+    end
+  end
+
+  context 'wiki project is in the user namespace' do
+    let(:project) { create(:project, namespace: create(:group, :public)) }
+
+    scenario 'user can update the wiki home page' do
+      click_link 'Edit'
+
+      expect(page).to have_content('Home · Edit Page')
+
+      fill_in :wiki_content, with: 'My awesome wiki!'
+      click_button 'Save changes'
+
+      expect(page).to have_content("Home · last edited by #{user.name}")
+      expect(page).to have_content('My awesome wiki!')
+    end
+  end
+end