Merge branch 'bw-commonmark-for-files' into 'master'

Enable CommonMark for files and wikis

See merge request gitlab-org/gitlab-ce!21228

25 files changed, 285 insertions, 52 deletions

diff --git a/app/helpers/markup_helper.rb b/app/helpers/markup_helper.rb
index cbb971cf8b7..3adaa1366c0 100644
--- a/app/helpers/markup_helper.rb
+++ b/app/helpers/markup_helper.rb
@@ -107,23 +107,23 @@ module MarkupHelper
 
   def markup(file_name, text, context = {})
     context[:project] ||= @project
-    context[:markdown_engine] ||= :redcarpet
+    context[:markdown_engine] ||= :redcarpet unless commonmark_for_repositories_enabled?
     html = context.delete(:rendered) || markup_unsafe(file_name, text, context)
     prepare_for_rendering(html, context)
   end
 
-  def render_wiki_content(wiki_page)
+  def render_wiki_content(wiki_page, context = {})
     text = wiki_page.content
     return '' unless text.present?
 
-    context = {
+    context.merge!(
       pipeline: :wiki,
       project: @project,
       project_wiki: @project_wiki,
       page_slug: wiki_page.slug,
-      issuable_state_filter_enabled: true,
-      markdown_engine: :redcarpet
-    }
+      issuable_state_filter_enabled: true
+    )
+    context[:markdown_engine] ||= :redcarpet unless commonmark_for_repositories_enabled?
 
     html =
       case wiki_page.format
@@ -178,6 +178,10 @@ module MarkupHelper
     end
   end
 
+  def commonmark_for_repositories_enabled?
+    Feature.enabled?(:commonmark_for_repositories, default_enabled: true)
+  end
+
   private
 
   # Return +text+, truncated to +max_chars+ characters, excluding any HTML
diff --git a/app/helpers/projects_helper.rb b/app/helpers/projects_helper.rb
index e0080b6660a..80b45176a62 100644
--- a/app/helpers/projects_helper.rb
+++ b/app/helpers/projects_helper.rb
@@ -252,6 +252,10 @@ module ProjectsHelper
     "xcode://clone?repo=#{CGI.escape(default_url_to_repo(project))}"
   end
 
+  def legacy_render_context(params)
+    params[:legacy_render] ? { markdown_engine: :redcarpet } : {}
+  end
+
   private
 
   def get_project_nav_tabs(project, current_user)
diff --git a/app/models/repository.rb b/app/models/repository.rb
index cf255c8951f..929d28b9d88 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -580,7 +580,12 @@ class Repository
   end
 
   def rendered_readme
-    MarkupHelper.markup_unsafe(readme.name, readme.data, project: project, markdown_engine: :redcarpet) if readme
+    return unless readme
+
+    context = { project: project }
+    context[:markdown_engine] = :redcarpet unless MarkupHelper.commonmark_for_repositories_enabled?
+
+    MarkupHelper.markup_unsafe(readme.name, readme.data, context)
   end
   cache_method :rendered_readme
 
diff --git a/app/services/preview_markdown_service.rb b/app/services/preview_markdown_service.rb
index 11b996ed4b6..de8757006f1 100644
--- a/app/services/preview_markdown_service.rb
+++ b/app/services/preview_markdown_service.rb
@@ -43,6 +43,10 @@ class PreviewMarkdownService < BaseService
   end
 
   def markdown_engine
-    CacheMarkdownField::MarkdownEngine.from_version(params[:markdown_version].to_i)
+    if params[:legacy_render]
+      :redcarpet
+    else
+      CacheMarkdownField::MarkdownEngine.from_version(params[:markdown_version].to_i)
+    end
   end
 end
diff --git a/app/views/projects/_wiki.html.haml b/app/views/projects/_wiki.html.haml
index 5646dc464f8..5adca007f7e 100644
--- a/app/views/projects/_wiki.html.haml
+++ b/app/views/projects/_wiki.html.haml
@@ -2,7 +2,7 @@
   %div{ class: container_class }
     .prepend-top-default.append-bottom-default
       .wiki
-        = render_wiki_content(@wiki_home)
+        = render_wiki_content(@wiki_home, legacy_render_context(params))
 - else
   - can_create_wiki = can?(current_user, :create_wiki, @project)
   .project-home-empty{ class: [('row-content-block' if can_create_wiki), ('content-block' unless can_create_wiki)] }
diff --git a/app/views/projects/blob/edit.html.haml b/app/views/projects/blob/edit.html.haml
index 27cf040da7c..fdab8a53b41 100644
--- a/app/views/projects/blob/edit.html.haml
+++ b/app/views/projects/blob/edit.html.haml
@@ -21,7 +21,7 @@
           Write
 
       %li
-        = link_to '#preview', 'data-preview-url' => project_preview_blob_path(@project, @id) do
+        = link_to '#preview', 'data-preview-url' => project_preview_blob_path(@project, @id, legacy_render: params[:legacy_render]) do
           = editing_preview_title(@blob.name)
 
     = form_tag(project_update_blob_path(@project, @id), method: :put, class: 'js-quick-submit js-requires-input js-edit-blob-form', data: blob_editor_paths) do
diff --git a/app/views/projects/blob/preview.html.haml b/app/views/projects/blob/preview.html.haml
index da2cef17e8a..eb65cd90ea8 100644
--- a/app/views/projects/blob/preview.html.haml
+++ b/app/views/projects/blob/preview.html.haml
@@ -2,7 +2,7 @@
   .diff-content
     - if markup?(@blob.name)
       .file-content.wiki
-        = markup(@blob.name, @content)
+        = markup(@blob.name, @content, legacy_render_context(params))
     - else
       .file-content.code.js-syntax-highlight
         - unless @diff_lines.empty?
diff --git a/app/views/projects/blob/viewers/_markup.html.haml b/app/views/projects/blob/viewers/_markup.html.haml
index 230305b488d..bd12cadf240 100644
--- a/app/views/projects/blob/viewers/_markup.html.haml
+++ b/app/views/projects/blob/viewers/_markup.html.haml
@@ -1,4 +1,6 @@
 - blob = viewer.blob
-- rendered_markup = blob.rendered_markup if blob.respond_to?(:rendered_markup)
+- context = legacy_render_context(params)
+- unless context[:markdown_engine] == :redcarpet
+  - context[:rendered] = blob.rendered_markup if blob.respond_to?(:rendered_markup)
 .file-content.wiki
-  = markup(blob.name, blob.data, rendered: rendered_markup)
+  = markup(blob.name, blob.data, context)
diff --git a/app/views/projects/wikis/_form.html.haml b/app/views/projects/wikis/_form.html.haml
index de692466fe5..7fb80450161 100644
--- a/app/views/projects/wikis/_form.html.haml
+++ b/app/views/projects/wikis/_form.html.haml
@@ -1,9 +1,13 @@
 - commit_message = @page.persisted? ? s_("WikiPageEdit|Update %{page_title}") : s_("WikiPageCreate|Create %{page_title}")
 - commit_message = commit_message % { page_title: @page.title }
+- if params[:legacy_render] || !commonmark_for_repositories_enabled?
+  - markdown_version = CacheMarkdownField::CACHE_REDCARPET_VERSION
+- else
+  - markdown_version = 0
 
 = form_for [@project.namespace.becomes(Namespace), @project, @page], method: @page.persisted? ? :put : :post,
            html: { class: 'wiki-form common-note-form prepend-top-default js-quick-submit' },
-           data: { markdown_version: CacheMarkdownField::CACHE_REDCARPET_VERSION } do |f|
+           data: { markdown_version: markdown_version } do |f|
   = form_errors(@page)
 
   - if @page.persisted?
diff --git a/app/views/projects/wikis/_sidebar.html.haml b/app/views/projects/wikis/_sidebar.html.haml
index 28353927135..02c5a6ea55c 100644
--- a/app/views/projects/wikis/_sidebar.html.haml
+++ b/app/views/projects/wikis/_sidebar.html.haml
@@ -12,7 +12,7 @@
     .blocks-container
       .block.block-first
         - if @sidebar_page
-          = render_wiki_content(@sidebar_page)
+          = render_wiki_content(@sidebar_page, legacy_render_context(params))
         - else
           %ul.wiki-pages
             = render @sidebar_wiki_entries, context: 'sidebar'
diff --git a/app/views/projects/wikis/show.html.haml b/app/views/projects/wikis/show.html.haml
index a08973c7f32..19b9744b508 100644
--- a/app/views/projects/wikis/show.html.haml
+++ b/app/views/projects/wikis/show.html.haml
@@ -26,6 +26,6 @@
 
 .prepend-top-default.append-bottom-default
   .wiki
-    = render_wiki_content(@page)
+    = render_wiki_content(@page, legacy_render_context(params))
 
 = render 'sidebar'
diff --git a/app/views/search/results/_snippet_blob.html.haml b/app/views/search/results/_snippet_blob.html.haml
index 57a0b64bfd5..8b95bdf9747 100644
--- a/app/views/search/results/_snippet_blob.html.haml
+++ b/app/views/search/results/_snippet_blob.html.haml
@@ -21,7 +21,7 @@
       .file-content.wiki
         - snippet_chunks.each do |chunk|
           - unless chunk[:data].empty?
-            = markup(snippet.file_name, chunk[:data])
+            = markup(snippet.file_name, chunk[:data], legacy_render_context(params))
           - else
             .file-content.code
               .nothing-here-block Empty file
diff --git a/changelogs/unreleased/bw-commonmark-for-files.yml b/changelogs/unreleased/bw-commonmark-for-files.yml
new file mode 100644
index 00000000000..f932ccb704f
--- /dev/null
+++ b/changelogs/unreleased/bw-commonmark-for-files.yml
@@ -0,0 +1,5 @@
+---
+title: Render files (`.md`) and wikis using CommonMark
+merge_request: 21228
+author:
+type: changed
diff --git a/doc/development/feature_flags.md b/doc/development/feature_flags.md
index 702caacc74f..6f757f1ce7b 100644
--- a/doc/development/feature_flags.md
+++ b/doc/development/feature_flags.md
@@ -58,13 +58,20 @@ Features that are developed and are intended to be merged behind a feature flag
 should not include a changelog entry. The entry should be added in the merge
 request removing the feature flags.
 
+In the rare case that you need the feature flag to be on automatically, use
+`default_enabled: true` when checking:
+
+```ruby
+Feature.enabled?(:feature_flag, project, default_enabled: true)
+```
+
 ### Specs
 
 In the test environment `Feature.enabled?` is stubbed to always respond to `true`,
 so we make sure behavior under feature flag doesn't go untested in some non-specific
 contexts.
- 
-If you need to test the feature flag in a different state, you need to stub it with: 
+
+If you need to test the feature flag in a different state, you need to stub it with:
 
 ```ruby
 stub_feature_flags(my_feature_flag: false)
diff --git a/lib/feature.rb b/lib/feature.rb
index 24dbcb32fc0..f4b57376313 100644
--- a/lib/feature.rb
+++ b/lib/feature.rb
@@ -42,13 +42,21 @@ class Feature
       persisted_names.include?(feature.name.to_s)
     end
 
-    def enabled?(key, thing = nil)
-      get(key).enabled?(thing)
+    # use `default_enabled: true` to default the flag to being `enabled`
+    # unless set explicitly.  The default is `disabled`
+    def enabled?(key, thing = nil, default_enabled: false)
+      feature = Feature.get(key)
+
+      # If we're not default enabling the flag or the feature has been set, always evaluate.
+      # `persisted?` can potentially generate DB queries and also checks for inclusion
+      # in an array of feature names (177 at last count), possibly reducing performance by half.
+      # So we only perform the `persisted` check if `default_enabled: true`
+      !default_enabled || Feature.persisted?(feature) ? feature.enabled?(thing) : true
     end
 
-    def disabled?(key, thing = nil)
+    def disabled?(key, thing = nil, default_enabled: false)
       # we need to make different method calls to make it easy to mock / define expectations in test mode
-      thing.nil? ? !enabled?(key) : !enabled?(key, thing)
+      thing.nil? ? !enabled?(key, default_enabled: default_enabled) : !enabled?(key, thing, default_enabled: default_enabled)
     end
 
     def enable(key, thing = true)
diff --git a/spec/features/projects/blobs/blob_show_spec.rb b/spec/features/projects/blobs/blob_show_spec.rb
index 1064f72c271..2ba4d4918ff 100644
--- a/spec/features/projects/blobs/blob_show_spec.rb
+++ b/spec/features/projects/blobs/blob_show_spec.rb
@@ -5,8 +5,8 @@ describe 'File blob', :js do
 
   let(:project) { create(:project, :public, :repository) }
 
-  def visit_blob(path, anchor: nil, ref: 'master')
-    visit project_blob_path(project, File.join(ref, path), anchor: anchor)
+  def visit_blob(path, anchor: nil, ref: 'master', legacy_render: nil)
+    visit project_blob_path(project, File.join(ref, path), anchor: anchor, legacy_render: legacy_render)
 
     wait_for_requests
   end
@@ -142,6 +142,52 @@ describe 'File blob', :js do
     end
   end
 
+  context 'Markdown rendering' do
+    before do
+      project.add_maintainer(project.creator)
+
+      Files::CreateService.new(
+        project,
+        project.creator,
+        start_branch: 'master',
+        branch_name: 'master',
+        commit_message: "Add RedCarpet and CommonMark Markdown ",
+        file_path: 'files/commonmark/file.md',
+        file_content: "1. one\n  - sublist\n"
+      ).execute
+    end
+
+    context 'when rendering default markdown' do
+      before do
+        visit_blob('files/commonmark/file.md')
+
+        wait_for_requests
+      end
+
+      it 'renders using CommonMark' do
+        aggregate_failures do
+          expect(page).to have_content("sublist")
+          expect(page).not_to have_xpath("//ol//li//ul")
+        end
+      end
+    end
+
+    context 'when rendering legacy markdown' do
+      before do
+        visit_blob('files/commonmark/file.md', legacy_render: 1)
+
+        wait_for_requests
+      end
+
+      it 'renders using RedCarpet' do
+        aggregate_failures do
+          expect(page).to have_content("sublist")
+          expect(page).to have_xpath("//ol//li//ul")
+        end
+      end
+    end
+  end
+
   context 'Markdown file (stored in LFS)' do
     before do
       project.add_maintainer(project.creator)
diff --git a/spec/features/projects/blobs/edit_spec.rb b/spec/features/projects/blobs/edit_spec.rb
index 0e036b4ea68..d5b20605860 100644
--- a/spec/features/projects/blobs/edit_spec.rb
+++ b/spec/features/projects/blobs/edit_spec.rb
@@ -7,6 +7,7 @@ describe 'Editing file blob', :js do
   let(:merge_request) { create(:merge_request, source_project: project, source_branch: 'feature', target_branch: 'master') }
   let(:branch) { 'master' }
   let(:file_path) { project.repository.ls_files(project.repository.root_ref)[1] }
+  let(:readme_file_path) { 'README.md' }
 
   context 'as a developer' do
     let(:user) { create(:user) }
@@ -20,14 +21,19 @@ describe 'Editing file blob', :js do
     def edit_and_commit(commit_changes: true)
       wait_for_requests
       find('.js-edit-blob').click
-      find('#editor')
-      execute_script('ace.edit("editor").setValue("class NextFeature\nend\n")')
+      fill_editor(content: "class NextFeature\\nend\\n")
 
       if commit_changes
         click_button 'Commit changes'
       end
     end
 
+    def fill_editor(content: "class NextFeature\\nend\\n")
+      wait_for_requests
+      find('#editor')
+      execute_script("ace.edit('editor').setValue('#{content}')")
+    end
+
     context 'from MR diff' do
       before do
         visit diffs_project_merge_request_path(project, merge_request)
@@ -63,6 +69,30 @@ describe 'Editing file blob', :js do
         expect(new_line_count).to be > 0
       end
     end
+
+    context 'when rendering the preview' do
+      it 'renders content with CommonMark' do
+        visit project_edit_blob_path(project, tree_join(branch, readme_file_path))
+        fill_editor(content: "1. one\\n  - sublist\\n")
+        click_link 'Preview'
+        wait_for_requests
+
+        # the above generates two seperate lists (not embedded) in CommonMark
+        expect(page).to have_content("sublist")
+        expect(page).not_to have_xpath("//ol//li//ul")
+      end
+
+      it 'renders content with RedCarpet when legacy_render is set' do
+        visit project_edit_blob_path(project, tree_join(branch, readme_file_path), legacy_render: 1)
+        fill_editor(content: "1. one\\n  - sublist\\n")
+        click_link 'Preview'
+        wait_for_requests
+
+        # the above generates a sublist list in RedCarpet
+        expect(page).to have_content("sublist")
+        expect(page).to have_xpath("//ol//li//ul")
+      end
+    end
   end
 
   context 'visit blob edit' do
diff --git a/spec/features/projects/wiki/markdown_preview_spec.rb b/spec/features/projects/wiki/markdown_preview_spec.rb
index ed5f8105487..f505023d1d0 100644
--- a/spec/features/projects/wiki/markdown_preview_spec.rb
+++ b/spec/features/projects/wiki/markdown_preview_spec.rb
@@ -162,6 +162,34 @@ describe 'Projects > Wiki > User previews markdown changes', :js do
         expect(page.html).to include("<a href=\"/#{project.full_path}/wikis/title%20with%20spaces\">spaced link</a>")
       end
     end
+
+    context 'when rendering the preview' do
+      it 'renders content with CommonMark' do
+        create_wiki_page 'a-page/b-page/c-page/common-mark'
+        click_link 'Edit'
+
+        fill_in :wiki_content, with: "1. one\n  - sublist\n"
+        click_on "Preview"
+
+        # the above generates two seperate lists (not embedded) in CommonMark
+        expect(page).to have_content("sublist")
+        expect(page).not_to have_xpath("//ol//li//ul")
+      end
+
+      it 'renders content with RedCarpet when legacy_render is set' do
+        wiki_page = create(:wiki_page,
+                           wiki: project.wiki,
+                           attrs: { title: 'home', content: "Empty content" })
+        visit(project_wiki_edit_path(project, wiki_page, legacy_render: 1))
+
+        fill_in :wiki_content, with: "1. one\n  - sublist\n"
+        click_on "Preview"
+
+        # the above generates a sublist list in RedCarpet
+        expect(page).to have_content("sublist")
+        expect(page).to have_xpath("//ol//li//ul")
+      end
+    end
   end
 
   it "does not linkify double brackets inside code blocks as expected" do
diff --git a/spec/features/snippets/show_spec.rb b/spec/features/snippets/show_spec.rb
index 3fe0b60b18f..367a479f62a 100644
--- a/spec/features/snippets/show_spec.rb
+++ b/spec/features/snippets/show_spec.rb
@@ -68,23 +68,45 @@ describe 'Snippet', :js do
         end
       end
 
-      context 'with cached Redcarpet html' do
-        let(:snippet) { create(:personal_snippet, :public, file_name: file_name, content: content, cached_markdown_version: CacheMarkdownField::CACHE_REDCARPET_VERSION) }
+      context 'Markdown rendering' do
+        let(:snippet) { create(:personal_snippet, :public, file_name: file_name, content: content) }
         let(:file_name) { 'test.md' }
         let(:content) { "1. one\n  - sublist\n" }
 
-        it 'renders correctly' do
-          expect(page).to have_xpath("//ol//li//ul")
+        context 'when rendering default markdown' do
+          it 'renders using CommonMark' do
+            expect(page).to have_content("sublist")
+            expect(page).not_to have_xpath("//ol//li//ul")
+          end
         end
-      end
 
-      context 'with cached CommonMark html' do
-        let(:snippet) { create(:personal_snippet, :public, file_name: file_name, content: content, cached_markdown_version: CacheMarkdownField::CACHE_COMMONMARK_VERSION) }
-        let(:file_name) { 'test.md' }
-        let(:content) { "1. one\n  - sublist\n" }
+        context 'when rendering legacy markdown' do
+          before do
+            visit snippet_path(snippet, legacy_render: 1)
 
-        it 'renders correctly' do
-          expect(page).not_to have_xpath("//ol//li//ul")
+            wait_for_requests
+          end
+
+          it 'renders using RedCarpet' do
+            expect(page).to have_content("sublist")
+            expect(page).to have_xpath("//ol//li//ul")
+          end
+        end
+
+        context 'with cached CommonMark html' do
+          let(:snippet) { create(:personal_snippet, :public, file_name: file_name, content: content, cached_markdown_version: CacheMarkdownField::CACHE_COMMONMARK_VERSION) }
+
+          it 'renders correctly' do
+            expect(page).not_to have_xpath("//ol//li//ul")
+          end
+        end
+
+        context 'with cached Redcarpet html' do
+          let(:snippet) { create(:personal_snippet, :public, file_name: file_name, content: content, cached_markdown_version: CacheMarkdownField::CACHE_REDCARPET_VERSION) }
+
+          it 'renders correctly' do
+            expect(page).to have_xpath("//ol//li//ul")
+          end
         end
       end
 
diff --git a/spec/helpers/markup_helper_spec.rb b/spec/helpers/markup_helper_spec.rb
index 597648b064d..9a29ac26eff 100644
--- a/spec/helpers/markup_helper_spec.rb
+++ b/spec/helpers/markup_helper_spec.rb
@@ -25,17 +25,17 @@ describe MarkupHelper do
       let(:actual) { "#{merge_request.to_reference} -> #{commit.to_reference} -> #{issue.to_reference}" }
 
       it "links to the merge request" do
-        expected = project_merge_request_path(project, merge_request)
+        expected = urls.project_merge_request_path(project, merge_request)
         expect(helper.markdown(actual)).to match(expected)
       end
 
       it "links to the commit" do
-        expected = project_commit_path(project, commit)
+        expected = urls.project_commit_path(project, commit)
         expect(helper.markdown(actual)).to match(expected)
       end
 
       it "links to the issue" do
-        expected = project_issue_path(project, issue)
+        expected = urls.project_issue_path(project, issue)
         expect(helper.markdown(actual)).to match(expected)
       end
     end
@@ -46,7 +46,7 @@ describe MarkupHelper do
       let(:second_issue) { create(:issue, project: second_project) }
 
       it 'links to the issue' do
-        expected = project_issue_path(second_project, second_issue)
+        expected = urls.project_issue_path(second_project, second_issue)
         expect(markdown(actual, project: second_project)).to match(expected)
       end
     end
@@ -93,7 +93,7 @@ describe MarkupHelper do
 
       # First issue link
       expect(doc.css('a')[1].attr('href'))
-        .to eq project_issue_path(project, issues[0])
+        .to eq urls.project_issue_path(project, issues[0])
       expect(doc.css('a')[1].text).to eq issues[0].to_reference
 
       # Internal commit link
@@ -102,7 +102,7 @@ describe MarkupHelper do
 
       # Second issue link
       expect(doc.css('a')[3].attr('href'))
-        .to eq project_issue_path(project, issues[1])
+        .to eq urls.project_issue_path(project, issues[1])
       expect(doc.css('a')[3].text).to eq issues[1].to_reference
 
       # Trailing commit link
@@ -128,7 +128,7 @@ describe MarkupHelper do
 
       # First issue link
       expect(doc.css('a')[1].attr('href'))
-        .to eq project_issue_path(project, issues[0])
+        .to eq urls.project_issue_path(project, issues[0])
       expect(doc.css('a')[1].text).to eq issues[0].to_reference
 
       # Internal commit link
@@ -137,7 +137,7 @@ describe MarkupHelper do
 
       # Second issue link
       expect(doc.css('a')[3].attr('href'))
-        .to eq project_issue_path(project, issues[1])
+        .to eq urls.project_issue_path(project, issues[1])
       expect(doc.css('a')[3].text).to eq issues[1].to_reference
 
       # Trailing commit link
@@ -183,7 +183,7 @@ describe MarkupHelper do
       doc = Nokogiri::HTML.parse(rendered)
 
       expect(doc.css('a')[0].attr('href'))
-        .to eq project_issue_path(project, issue)
+        .to eq urls.project_issue_path(project, issue)
       expect(doc.css('a')[0].text).to eq issue.to_reference
 
       wrapped = helper.link_to_html(rendered, link)
@@ -207,6 +207,17 @@ describe MarkupHelper do
 
       expect(helper).to receive(:markdown_unsafe).with('wiki content',
         pipeline: :wiki, project: project, project_wiki: @wiki, page_slug: "nested/page",
+        issuable_state_filter_enabled: true)
+
+      helper.render_wiki_content(@wiki)
+    end
+
+    it 'uses Wiki pipeline for markdown files with RedCarpet if feature disabled' do
+      stub_feature_flags(commonmark_for_repositories: false)
+      allow(@wiki).to receive(:format).and_return(:markdown)
+
+      expect(helper).to receive(:markdown_unsafe).with('wiki content',
+        pipeline: :wiki, project: project, project_wiki: @wiki, page_slug: "nested/page",
         issuable_state_filter_enabled: true, markdown_engine: :redcarpet)
 
       helper.render_wiki_content(@wiki)
@@ -259,10 +270,18 @@ describe MarkupHelper do
       expect(helper.markup('foo.md', content, rendered: '<p>NOEL</p>')).to eq('<p>NOEL</p>')
     end
 
-    it 'defaults to Redcarpet' do
-      expect(helper).to receive(:markdown_unsafe).with(content, hash_including(markdown_engine: :redcarpet)).and_return('NOEL')
+    it 'defaults to CommonMark' do
+      expect(helper.markup('foo.md', 'x^2')).to include('x^2')
+    end
 
-      expect(helper.markup('foo.md', content)).to eq('NOEL')
+    it 'honors markdown_engine for RedCarpet' do
+      expect(helper.markup('foo.md', 'x^2', { markdown_engine: :redcarpet })).to include('x<sup>2</sup>')
+    end
+
+    it 'uses RedCarpet if feature disabled' do
+      stub_feature_flags(commonmark_for_repositories: false)
+
+      expect(helper.markup('foo.md', 'x^2', { markdown_engine: :redcarpet })).to include('x<sup>2</sup>')
     end
   end
 
@@ -414,4 +433,8 @@ describe MarkupHelper do
       expect(helper.cross_project_reference(project, issue)).to include(project.full_path)
     end
   end
+
+  def urls
+    Gitlab::Routing.url_helpers
+  end
 end
diff --git a/spec/helpers/projects_helper_spec.rb b/spec/helpers/projects_helper_spec.rb
index cbd4ff0fb4a..976b6c312b4 100644
--- a/spec/helpers/projects_helper_spec.rb
+++ b/spec/helpers/projects_helper_spec.rb
@@ -470,4 +470,16 @@ describe ProjectsHelper do
       end
     end
   end
+
+  describe '#legacy_render_context' do
+    it 'returns the redcarpet engine' do
+      params = { legacy_render: '1' }
+
+      expect(helper.legacy_render_context(params)).to include(markdown_engine: :redcarpet)
+    end
+
+    it 'returns nothing' do
+      expect(helper.legacy_render_context({})).to be_empty
+    end
+  end
 end
diff --git a/spec/lib/banzai/pipeline/wiki_pipeline_spec.rb b/spec/lib/banzai/pipeline/wiki_pipeline_spec.rb
index 88ae4c1e07a..52b8c9be647 100644
--- a/spec/lib/banzai/pipeline/wiki_pipeline_spec.rb
+++ b/spec/lib/banzai/pipeline/wiki_pipeline_spec.rb
@@ -121,6 +121,13 @@ describe Banzai::Pipeline::WikiPipeline do
               expect(output).to include("href=\"#{relative_url_root}/wiki_link_ns/wiki_link_project/wikis/page\"")
             end
 
+            it 'rewrites non-file links (with spaces) to be at the scope of the wiki root' do
+              markdown = "[Link to Page](page slug)"
+              output = described_class.to_html(markdown, project: project, project_wiki: project_wiki, page_slug: page.slug)
+
+              expect(output).to include("href=\"#{relative_url_root}/wiki_link_ns/wiki_link_project/wikis/page%20slug\"")
+            end
+
             it "rewrites file links to be at the scope of the current directory" do
               markdown = "[Link to Page](page.md)"
               output = described_class.to_html(markdown, project: project, project_wiki: project_wiki, page_slug: page.slug)
@@ -134,6 +141,13 @@ describe Banzai::Pipeline::WikiPipeline do
 
               expect(output).to include("href=\"#{relative_url_root}/wiki_link_ns/wiki_link_project/wikis/start-page#title\"")
             end
+
+            it 'rewrites links (with spaces) with anchor' do
+              markdown = '[Link to Header](start page#title)'
+              output = described_class.to_html(markdown, project: project, project_wiki: project_wiki, page_slug: page.slug)
+
+              expect(output).to include("href=\"#{relative_url_root}/wiki_link_ns/wiki_link_project/wikis/start%20page#title\"")
+            end
           end
 
           describe "when creating root links" do
diff --git a/spec/lib/feature_spec.rb b/spec/lib/feature_spec.rb
index 8bb5a843484..48c0ba8a653 100644
--- a/spec/lib/feature_spec.rb
+++ b/spec/lib/feature_spec.rb
@@ -119,6 +119,10 @@ describe Feature do
       expect(described_class.enabled?(:some_random_feature_flag)).to be_falsey
     end
 
+    it 'returns true for undefined feature with default_enabled' do
+      expect(described_class.enabled?(:some_random_feature_flag, default_enabled: true)).to be_truthy
+    end
+
     it 'returns false for existing disabled feature in the database' do
       described_class.disable(:disabled_feature_flag)
 
@@ -160,6 +164,10 @@ describe Feature do
       expect(described_class.disabled?(:some_random_feature_flag)).to be_truthy
     end
 
+    it 'returns false for undefined feature with default_enabled' do
+      expect(described_class.disabled?(:some_random_feature_flag, default_enabled: true)).to be_falsey
+    end
+
     it 'returns true for existing disabled feature in the database' do
       described_class.disable(:disabled_feature_flag)
 
diff --git a/spec/services/preview_markdown_service_spec.rb b/spec/services/preview_markdown_service_spec.rb
index 507909d9231..b69977c812a 100644
--- a/spec/services/preview_markdown_service_spec.rb
+++ b/spec/services/preview_markdown_service_spec.rb
@@ -101,4 +101,11 @@ describe PreviewMarkdownService do
 
     expect(result[:markdown_engine]).to eq :common_mark
   end
+
+  it 'honors the legacy_render parameter' do
+    service = described_class.new(project, user, { legacy_render: '1' })
+    result  = service.execute
+
+    expect(result[:markdown_engine]).to eq :redcarpet
+  end
 end
diff --git a/spec/support/helpers/stub_feature_flags.rb b/spec/support/helpers/stub_feature_flags.rb
index c54a871b157..4061a8d1bc9 100644
--- a/spec/support/helpers/stub_feature_flags.rb
+++ b/spec/support/helpers/stub_feature_flags.rb
@@ -4,8 +4,8 @@ module StubFeatureFlags
   # @param [Hash] features where key is feature name and value is boolean whether enabled or not
   def stub_feature_flags(features)
     features.each do |feature_name, enabled|
-      allow(Feature).to receive(:enabled?).with(feature_name) { enabled }
-      allow(Feature).to receive(:enabled?).with(feature_name.to_s) { enabled }
+      allow(Feature).to receive(:enabled?).with(feature_name, any_args) { enabled }
+      allow(Feature).to receive(:enabled?).with(feature_name.to_s, any_args) { enabled }
     end
   end
 end