Make sure wiki exists when it's enabled

app/services/projects/update_service.rb

@@ -15,6 +15,8 @@ module Projects
         return error("Could not set the default branch") unless project.change_head(params[:default_branch])
       end
 
+      ensure_wiki_exists if enabling_wiki?
+
       if project.update_attributes(params.except(:default_branch))
         if project.previous_changes.include?('path')
           project.rename_repo
@@ -52,5 +54,18 @@ module Projects
       project.repository.exists? &&
         new_branch && new_branch != project.default_branch
     end
+
+    def enabling_wiki?
+      return false if @project.wiki_enabled?
+
+      params[:project_feature_attributes][:wiki_access_level].to_i > ProjectFeature::DISABLED
+    end
+
+    def ensure_wiki_exists
+      ProjectWiki.new(project, project.owner).wiki
+    rescue ProjectWiki::CouldNotCreateWikiError
+      log_error("Could not create wiki for #{project.full_name}")
+      Gitlab::Metrics.counter(:wiki_can_not_be_created_total, 'Counts the times we failed to create a wiki')
+    end
   end
 end

spec/services/projects/update_service_spec.rb

@@ -123,6 +123,29 @@ describe Projects::UpdateService do
       end
     end
 
+    context 'when enabling a wiki' do
+      it 'creates a wiki' do
+        project.project_feature.update(wiki_access_level: ProjectFeature::DISABLED)
+        FileUtils.rm_rf(project.wiki.repository.path)
+
+        result = update_project(project, user, project_feature_attributes: { wiki_access_level: ProjectFeature::ENABLED })
+
+        expect(result).to eq({ status: :success })
+        expect(project.wiki_repository_exists?).to be true
+        expect(project.wiki_enabled?).to be true
+      end
+
+      it 'logs an error and creates a metric when wiki can not be created' do
+        project.project_feature.update(wiki_access_level: ProjectFeature::DISABLED)
+
+        expect_any_instance_of(ProjectWiki).to receive(:wiki).and_raise(ProjectWiki::CouldNotCreateWikiError)
+        expect_any_instance_of(described_class).to receive(:log_error).with("Could not create wiki for #{project.full_name}")
+        expect(Gitlab::Metrics).to receive(:counter)
+
+        update_project(project, user, project_feature_attributes: { wiki_access_level: ProjectFeature::ENABLED })
+      end
+    end
+
     context 'when updating a project that contains container images' do
       before do
         stub_container_registry_config(enabled: true)