fix error links in help page

app/controllers/help_controller.rb

@@ -7,8 +7,8 @@ class HelpController < ApplicationController
     @help_index = File.read(Rails.root.join('doc', 'README.md'))
 
     # Prefix Markdown links with `help/` unless they already have been
-    # See http://rubular.com/r/nwwhzH6Z8X
+    # See http://rubular.com/r/ie2MlpdUMq
-    @help_index.gsub!(/(\]\()(?!help\/)([^\)\(]+)(\))/, '\1help/\2\3')
+    @help_index.gsub!(/(\]\()(\/?help\/)?([^\)\(]+\))/, '\1/help/\3')
   end
 
   def show

changelogs/unreleased/fix-help-page-links.yml

@@ -0,0 +1,4 @@
+---
+title: Fix error links in help index page
+merge_request: 7396
+author: Fu Xu

spec/controllers/help_controller_spec.rb

@@ -7,6 +7,40 @@ describe HelpController do
     sign_in(user)
   end
 
+  describe 'GET #index' do
+    context 'when url prefixed without /help/' do
+      it 'has correct url prefix' do
+        stub_readme("[API](api/README.md)")
+        get :index
+        expect(assigns[:help_index]).to eq '[API](/help/api/README.md)'
+      end
+    end
+
+    context 'when url prefixed with help/' do
+      it 'will be an absolute path' do
+        stub_readme("[API](help/api/README.md)")
+        get :index
+        expect(assigns[:help_index]).to eq '[API](/help/api/README.md)'
+      end
+    end
+
+    context 'when url prefixed with help' do
+      it 'will be an absolute path' do
+        stub_readme("[API](helpful_hints/README.md)")
+        get :index
+        expect(assigns[:help_index]).to eq '[API](/help/helpful_hints/README.md)'
+      end
+    end
+
+    context 'when url prefixed with /help/' do
+      it 'will not be changed' do
+        stub_readme("[API](/help/api/README.md)")
+        get :index
+        expect(assigns[:help_index]).to eq '[API](/help/api/README.md)'
+      end
+    end
+  end
+
   describe 'GET #show' do
     context 'for Markdown formats' do
       context 'when requested file exists' do
@@ -72,4 +106,8 @@ describe HelpController do
       end
     end
   end
+
+  def stub_readme(content)
+    allow(File).to receive(:read).and_return(content)
+  end
 end