render using RedCarpet if legacy_render parameter is set

app/helpers/markup_helper.rb

@@ -111,17 +111,17 @@ module MarkupHelper
     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
-    }
+    })
 
     html =
       case wiki_page.format

app/services/preview_markdown_service.rb

@@ -43,6 +43,10 @@ class PreviewMarkdownService < BaseService
   end
 
   def markdown_engine
+    if params[:legacy_render]
+      :redcarpet
+    else
       CacheMarkdownField::MarkdownEngine.from_version(params[:markdown_version].to_i)
     end
+  end
 end

app/views/projects/_wiki.html.haml

@@ -2,7 +2,8 @@
   %div{ class: container_class }
     .prepend-top-default.append-bottom-default
       .wiki
-        = render_wiki_content(@wiki_home)
+        - context = params[:legacy_render] ? { markdown_engine: :redcarpet} : {}
+        = render_wiki_content(@wiki_home, context)
 - 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)] }

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

app/views/projects/blob/preview.html.haml

@@ -2,7 +2,8 @@
   .diff-content
     - if markup?(@blob.name)
       .file-content.wiki
-        = markup(@blob.name, @content)
+        - context = params[:legacy_render] ? { markdown_engine: :redcarpet} : {}
+        = markup(@blob.name, @content, context)
     - else
       .file-content.code.js-syntax-highlight
         - unless @diff_lines.empty?

app/views/projects/blob/viewers/_markup.html.haml

 - blob = viewer.blob
-- rendered_markup = blob.rendered_markup if blob.respond_to?(:rendered_markup)
+- context = {}
+- if params[:legacy_render]
+  - context[:markdown_engine] = :redcarpet
+- else
+  - 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)

app/views/projects/wikis/_form.html.haml

 - commit_message = @page.persisted? ? s_("WikiPageEdit|Update %{page_title}") : s_("WikiPageCreate|Create %{page_title}")
 - commit_message = commit_message % { page_title: @page.title }
+- markdown_version = params[:legacy_render] ? CacheMarkdownField::CACHE_REDCARPET_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' } do |f|
+           html: { class: 'wiki-form common-note-form prepend-top-default js-quick-submit' },
+           data: { markdown_version: markdown_version } do |f|
   = form_errors(@page)
 
   - if @page.persisted?

app/views/projects/wikis/_sidebar.html.haml

@@ -12,7 +12,8 @@
     .blocks-container
       .block.block-first
         - if @sidebar_page
-          = render_wiki_content(@sidebar_page)
+          - context = params[:legacy_render] ? { markdown_engine: :redcarpet} : {}
+          = render_wiki_content(@sidebar_page, context)
         - else
           %ul.wiki-pages
             = render @sidebar_wiki_entries, context: 'sidebar'

app/views/projects/wikis/show.html.haml

@@ -26,6 +26,7 @@
 
 .prepend-top-default.append-bottom-default
   .wiki
-    = render_wiki_content(@page)
+    - context = params[:legacy_render] ? { markdown_engine: :redcarpet} : {}
+    = render_wiki_content(@page, context)
 
 = render 'sidebar'

app/views/search/results/_snippet_blob.html.haml

@@ -21,7 +21,8 @@
       .file-content.wiki
         - snippet_chunks.each do |chunk|
           - unless chunk[:data].empty?
-            = markup(snippet.file_name, chunk[:data])
+            - context = params[:legacy_render] ? { markdown_engine: :redcarpet} : {}
+            = markup(snippet.file_name, chunk[:data], context)
           - else
             .file-content.code
               .nothing-here-block Empty file

changelogs/unreleased/bw-commonmark-for-files.yml

+---
+title: Render files (`.md`) and wikis using CommonMark
+merge_request: 21228
+author:
+type: changed

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)

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

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

spec/features/snippets/show_spec.rb

@@ -68,26 +68,48 @@ 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
+        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
+
+        context 'when rendering legacy markdown' do
+          before do
+            visit snippet_path(snippet, legacy_render: 1)
+
+            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) }
-        let(:file_name) { 'test.md' }
-        let(:content) { "1. one\n  - sublist\n" }
 
           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
+
       context 'switching to the simple viewer' do
         before do
           find('.js-blob-viewer-switch-btn[data-viewer=simple]').click

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