Use sentry configuration from UI settings

This change uses Gitlab::CurrentSettings to configure sentry on client
when `enable_new_sentry_clientside_integration` is enabled.

Conversely, it also allows users to disable the old integration sentry
by disabling `enable_old_sentry_clientside_integration`.

When both options are enabled, settings take precedence over config.

config/feature_flags/development/enable_new_sentry_clientside_integration.yml

+---
+name: enable_new_sentry_clientside_integration
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/102650
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/344832
+milestone: '15.6'
+type: development
+group: group::runner
+default_enabled: false

config/feature_flags/development/enable_old_sentry_clientside_integration.yml

+---
+name: enable_old_sentry_clientside_integration
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/102650
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/344832
+milestone: '15.6'
+type: development
+group: group::runner
+default_enabled: true

lib/gitlab/gon_helper.rb

@@ -17,11 +17,18 @@ def add_gon_variables
       gon.markdown_surround_selection = current_user&.markdown_surround_selection
       gon.markdown_automatic_lists = current_user&.markdown_automatic_lists
 
-      if Gitlab.config.sentry.enabled
+      # Support for Sentry setup via configuration will be removed in 16.0
+      # in favor of Gitlab::CurrentSettings.
+      if Feature.enabled?(:enable_old_sentry_clientside_integration) && Gitlab.config.sentry.enabled
         gon.sentry_dsn           = Gitlab.config.sentry.clientside_dsn
         gon.sentry_environment   = Gitlab.config.sentry.environment
       end
 
+      if Feature.enabled?(:enable_new_sentry_clientside_integration) && Gitlab::CurrentSettings.sentry_enabled
+        gon.sentry_dsn           = Gitlab::CurrentSettings.sentry_clientside_dsn
+        gon.sentry_environment   = Gitlab::CurrentSettings.sentry_environment
+      end
+
       gon.recaptcha_api_server_url = ::Recaptcha.configuration.api_server_url
       gon.recaptcha_sitekey      = Gitlab::CurrentSettings.recaptcha_site_key
       gon.gitlab_url             = Gitlab.config.gitlab.url

spec/lib/gitlab/gon_helper_spec.rb

@@ -39,6 +39,72 @@ def current_user
         helper.add_gon_variables
       end
     end
+
+    describe 'sentry configuration' do
+      let(:legacy_clientside_dsn) { 'https://xxx@sentry-legacy.example.com/1' }
+      let(:clientside_dsn) { 'https://xxx@sentry.example.com/1' }
+      let(:environment) { 'production' }
+
+      context 'with enable_old_sentry_clientside_integration enabled' do
+        before do
+          stub_feature_flags(
+            enable_old_sentry_clientside_integration: true,
+            enable_new_sentry_clientside_integration: false
+          )
+
+          stub_config(sentry: { enabled: true, clientside_dsn: legacy_clientside_dsn, environment: environment })
+        end
+
+        it 'sets sentry dsn and environment from config' do
+          expect(gon).to receive(:sentry_dsn=).with(legacy_clientside_dsn)
+          expect(gon).to receive(:sentry_environment=).with(environment)
+
+          helper.add_gon_variables
+        end
+      end
+
+      context 'with enable_new_sentry_clientside_integration enabled' do
+        before do
+          stub_feature_flags(
+            enable_old_sentry_clientside_integration: false,
+            enable_new_sentry_clientside_integration: true
+          )
+
+          stub_application_setting(sentry_enabled: true)
+          stub_application_setting(sentry_clientside_dsn: clientside_dsn)
+          stub_application_setting(sentry_environment: environment)
+        end
+
+        it 'sets sentry dsn and environment from application settings' do
+          expect(gon).to receive(:sentry_dsn=).with(clientside_dsn)
+          expect(gon).to receive(:sentry_environment=).with(environment)
+
+          helper.add_gon_variables
+        end
+      end
+
+      context 'with enable_old_sentry_clientside_integration and enable_new_sentry_clientside_integration enabled' do
+        before do
+          stub_feature_flags(
+            enable_old_sentry_clientside_integration: true,
+            enable_new_sentry_clientside_integration: true
+          )
+
+          stub_config(sentry: { enabled: true, clientside_dsn: legacy_clientside_dsn, environment: environment })
+
+          stub_application_setting(sentry_enabled: true)
+          stub_application_setting(sentry_clientside_dsn: clientside_dsn)
+          stub_application_setting(sentry_environment: environment)
+        end
+
+        it 'sets sentry dsn and environment from application settings' do
+          expect(gon).to receive(:sentry_dsn=).with(clientside_dsn)
+          expect(gon).to receive(:sentry_environment=).with(environment)
+
+          helper.add_gon_variables
+        end
+      end
+    end
   end
 
   describe '#push_frontend_feature_flag' do