Add configuration option support for documentation pages

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/214164

We want to introduce an option to configure documentation pages base
url via gitlab.yml file. That will allow us to provide custom
configurations for different distributions (Omnibus, source code
installation, etc.)

app/controllers/help_controller.rb

@@ -84,7 +84,16 @@ class HelpController < ApplicationController
   end
 
   def documentation_base_url
-    @documentation_base_url ||= Gitlab::CurrentSettings.current_application_settings.help_page_documentation_base_url.presence
+    @documentation_base_url ||= documentation_base_url_from_yml_configuration || documentation_base_url_from_db
+  end
+
+  # DEPRECATED
+  def documentation_base_url_from_db
+    Gitlab::CurrentSettings.current_application_settings.help_page_documentation_base_url.presence
+  end
+
+  def documentation_base_url_from_yml_configuration
+    ::Gitlab.config.gitlab_docs.host.presence if ::Gitlab.config.gitlab_docs.enabled
   end
 
   def documentation_file_path

config/initializers/1_settings.rb

@@ -310,6 +310,13 @@ Settings.pages['secret_file'] ||= Rails.root.join('.gitlab_pages_secret')
 Settings.pages['storage_path']      = Settings.pages['path']
 Settings.pages['object_store']      = ObjectStoreSettings.legacy_parse(Settings.pages['object_store'])
 
+#
+# GitLab documentation
+#
+Settings['gitlab_docs'] ||= Settingslogic.new({})
+Settings.gitlab_docs['enabled'] ||= false
+Settings.gitlab_docs['host'] = nil unless Settings.gitlab_docs.enabled
+
 #
 # Geo
 #

spec/controllers/help_controller_spec.rb

@@ -7,6 +7,43 @@ RSpec.describe HelpController do
 
   let(:user) { create(:user) }
 
+  shared_examples 'documentation pages local render' do
+    it 'renders HTML' do
+      aggregate_failures do
+        is_expected.to render_template('show.html.haml')
+        expect(response.media_type).to eq 'text/html'
+      end
+    end
+  end
+
+  shared_examples 'documentation pages redirect' do |documentation_base_url|
+    let(:gitlab_version) { '13.4.0-ee' }
+
+    before do
+      stub_version(gitlab_version, 'ignored_revision_value')
+    end
+
+    it 'redirects user to custom documentation url with a specified version' do
+      is_expected.to redirect_to("#{documentation_base_url}/13.4/ee/#{path}.html")
+    end
+
+    context 'when it is a pre-release' do
+      let(:gitlab_version) { '13.4.0-pre' }
+
+      it 'redirects user to custom documentation url without a version' do
+        is_expected.to redirect_to("#{documentation_base_url}/ee/#{path}.html")
+      end
+    end
+
+    context 'when feature flag is disabled' do
+      before do
+        stub_feature_flags(help_page_documentation_redirect: false)
+      end
+
+      it_behaves_like 'documentation pages local render'
+    end
+  end
+
   before do
     sign_in(user)
   end
@@ -99,69 +136,70 @@ RSpec.describe HelpController do
 
   describe 'GET #show' do
     context 'for Markdown formats' do
+      subject { get :show, params: { path: path }, format: :md }
+
+      let(:path) { 'ssh/README' }
+
       context 'when requested file exists' do
         before do
           expect_file_read(File.join(Rails.root, 'doc/ssh/README.md'), content: fixture_file('blockquote_fence_after.md'))
 
-          get :show, params: { path: 'ssh/README' }, format: :md
+          subject
         end
 
         it 'assigns to @markdown' do
           expect(assigns[:markdown]).not_to be_empty
         end
 
-        it 'renders HTML' do
-          aggregate_failures do
-            expect(response).to render_template('show.html.haml')
-            expect(response.media_type).to eq 'text/html'
-          end
-        end
+        it_behaves_like 'documentation pages local render'
       end
 
-      context 'when a custom help_page_documentation_url is set' do
+      context 'when a custom help_page_documentation_url is set in database' do
         before do
-          stub_application_setting(help_page_documentation_base_url: documentation_base_url)
-          stub_version(gitlab_version, 'deadbeaf')
+          stub_application_setting(help_page_documentation_base_url: 'https://in-db.gitlab.com')
         end
 
-        subject { get :show, params: { path: path }, format: 'html' }
+        it_behaves_like 'documentation pages redirect', 'https://in-db.gitlab.com'
+      end
 
-        let(:gitlab_version) { '13.4.0-ee' }
-        let(:documentation_base_url) { 'https://docs.gitlab.com' }
-        let(:path) { 'ssh/README' }
+      context 'when a custom help_page_documentation_url is set in configuration file' do
+        let(:host) { 'https://in-yaml.gitlab.com' }
+        let(:docs_enabled) { true }
 
-        it 'redirects user to custom documentation url with a specified version' do
-          is_expected.to redirect_to("#{documentation_base_url}/13.4/ee/#{path}.html")
+        before do
+          allow(Settings).to receive(:gitlab_docs) { double(enabled: docs_enabled, host: host) }
         end
 
-        context 'when documentation url ends with a slash' do
-          let(:documentation_base_url) { 'https://docs.gitlab.com/' }
+        it_behaves_like 'documentation pages redirect', 'https://in-yaml.gitlab.com'
 
-          it 'redirects user to custom documentation url without slash duplicates' do
-            is_expected.to redirect_to("https://docs.gitlab.com/13.4/ee/#{path}.html")
-          end
+        context 'when gitlab_docs is disabled' do
+          let(:docs_enabled) { false }
+
+          it_behaves_like 'documentation pages local render'
         end
 
-        context 'when it is a pre-release' do
-          let(:gitlab_version) { '13.4.0-pre' }
+        context 'when host is missing' do
+          let(:host) { nil }
 
-          it 'redirects user to custom documentation url without a version' do
-            is_expected.to redirect_to("#{documentation_base_url}/ee/#{path}.html")
-          end
+          it_behaves_like 'documentation pages local render'
         end
+      end
 
-        context 'when feature flag is disabled' do
-          before do
-            stub_feature_flags(help_page_documentation_redirect: false)
-          end
+      context 'when help_page_documentation_url is set in both db and configuration file' do
+        before do
+          stub_application_setting(help_page_documentation_base_url: 'https://in-db.gitlab.com')
+          allow(Settings).to receive(:gitlab_docs) { double(enabled: true, host: 'https://in-yaml.gitlab.com') }
+        end
 
-          it 'renders HTML' do
-            aggregate_failures do
-              is_expected.to render_template('show.html.haml')
-              expect(response.media_type).to eq 'text/html'
-            end
-          end
+        it_behaves_like 'documentation pages redirect', 'https://in-yaml.gitlab.com'
+      end
+
+      context 'when help_page_documentation_url has a trailing slash' do
+        before do
+          allow(Settings).to receive(:gitlab_docs) { double(enabled: true, host: 'https://in-yaml.gitlab.com/') }
         end
+
+        it_behaves_like 'documentation pages redirect', 'https://in-yaml.gitlab.com'
       end
 
       context 'when requested file is missing' do