Merge branch 'fix-broken-links-in-help' into 'master'

Fix broken links on help page

Closes #57554

See merge request gitlab-org/gitlab-ce!25120

app/controllers/help_controller.rb

@@ -13,9 +13,10 @@ class HelpController < ApplicationController
     # Remove YAML frontmatter so that it doesn't look weird
     @help_index = File.read(Rails.root.join('doc', 'README.md')).sub(YAML_FRONT_MATTER_REGEXP, '')
 
-    # Prefix Markdown links with `help/` unless they are external links
-    # See http://rubular.com/r/X3baHTbPO2
-    @help_index.gsub!(%r{(?<delim>\]\()(?!.+://)(?!/)(?<link>[^\)\(]+\))}) do
+    # Prefix Markdown links with `help/` unless they are external links.
+    # '//' not necessarily part of URL, e.g., mailto:mail@example.com
+    # See https://rubular.com/r/DFHZl5w8d3bpzV
+    @help_index.gsub!(%r{(?<delim>\]\()(?!\w+:)(?!/)(?<link>[^\)\(]+\))}) do
       "#{$~[:delim]}#{Gitlab.config.gitlab.relative_url_root}/help/#{$~[:link]}"
     end
   end

spec/controllers/help_controller_spec.rb

@@ -37,6 +37,46 @@ describe HelpController do
         expect(assigns[:help_index]).to eq '[external](https://some.external.link)'
       end
     end
+
+    context 'when relative url with external on same line' do
+      it 'prefix it with /help/' do
+        stub_readme("[API](api/README.md) [external](https://some.external.link)")
+
+        get :index
+
+        expect(assigns[:help_index]).to eq '[API](/help/api/README.md) [external](https://some.external.link)'
+      end
+    end
+
+    context 'when relative url with http:// in query' do
+      it 'prefix it with /help/' do
+        stub_readme("[API](api/README.md?go=https://example.com/)")
+
+        get :index
+
+        expect(assigns[:help_index]).to eq '[API](/help/api/README.md?go=https://example.com/)'
+      end
+    end
+
+    context 'when mailto URL' do
+      it 'do not change it' do
+        stub_readme("[report bug](mailto:bugs@example.com)")
+
+        get :index
+
+        expect(assigns[:help_index]).to eq '[report bug](mailto:bugs@example.com)'
+      end
+    end
+
+    context 'when protocol-relative link' do
+      it 'do not change it' do
+        stub_readme("[protocol-relative](//example.com)")
+
+        get :index
+
+        expect(assigns[:help_index]).to eq '[protocol-relative](//example.com)'
+      end
+    end
   end
 
   describe 'GET #show' do