Wrap sourcegraph in feature flag and user opt-in

```---------
DB Migration
```

---------

This commit contains a DB migration adding the following fields:

- `applicaiton_settings::sourcegraph_public_only` this is helpful for
managing the difference between self-hosted and gitlab.com, where on
.com Sourcegraph is not authorized to see private projects, but in a
self-hosted instance, it's based on the authentication token they
preconfigure with their private sourcegraph instance.

- `user_preferences::sourcegraph_enabled` this is used to determine
if the user has opted in for sourcegraph or not.

------------
Feature flag
------------

Example:

```
Feature.enable(:sourcegraph, Project.find_by_full_path('lorem/ipsum'))
```

It is possible to conditionally apply this feature flag, so that the
bundle is only loaded on certain projects. This makes showing the admin
(or user) settings based on this flag difficult since there is no project
or group in scope for these views. For this reason, we've introduced the
`Gitlab::Sourcegraph` module to encapsulate whether a feature is
available (conditionally or globally).

How?

Conditional or global enablement can be tested with:

```
!Feature.get(:sourcegraph).off?
```

https://github.com/jnunemaker/flipper/blob/fa78a0030c7f139aecc3f9c8468baf9fd1498eb9/lib/flipper/feature.rb#L223

----
Also
----

The bundle is only loaded in project routes (potential for further optimization here)

app/assets/javascripts/main.js

@@ -33,7 +33,6 @@ import initBreadcrumbs from './breadcrumb';
 import initUsagePingConsent from './usage_ping_consent';
 import initPerformanceBar from './performance_bar';
 import initSearchAutocomplete from './search_autocomplete';
-import initSourcegraph from './sourcegraph';
 import GlFieldErrors from './gl_field_errors';
 import initUserPopovers from './user_popovers';
 import { initUserTracking } from './tracking';
@@ -161,10 +160,6 @@ function deferredInitialisation() {
   });
 
   loadAwardsHandler();
-
-  if (gon.sourcegraph_enabled) {
-    initSourcegraph();
-  }
 }
 
 document.addEventListener('DOMContentLoaded', () => {

app/assets/javascripts/pages/projects/index.js

+import initSourcegraph from '~/sourcegraph';
 import Project from './project';
 import ShortcutsNavigation from '../../behaviors/shortcuts/shortcuts_navigation';
 import initCreateCluster from '~/create_cluster/init_create_cluster';
@@ -7,4 +8,6 @@ document.addEventListener('DOMContentLoaded', () => {
 
   new Project(); // eslint-disable-line no-new
   new ShortcutsNavigation(); // eslint-disable-line no-new
+
+  initSourcegraph();
 });

app/assets/javascripts/sourcegraph.js → app/assets/javascripts/sourcegraph/index.js

+function loadScript(path) {
+  const script = document.createElement('script');
+  script.type = 'application/javascript';
+  script.src = path;
+  script.defer = true;
+  document.head.appendChild(script);
+}
+
 /**
  * Loads the Sourcegraph integration for support for Sourcegraph extensions and
  * code intelligence.
  */
 export default function initSourcegraph() {
-  const sourcegraphUrl = gon.sourcegraph_url;
+  const { sourcegraph_url: sourcegraphUrl, sourcegraph_enabled: sourcegraphEnabled } = gon;
+
+  if (!sourcegraphEnabled || !sourcegraphUrl) {
+    return;
+  }
+
   const assetsUrl = new URL('/assets/webpack/sourcegraph/', window.location.href);
+  const scriptPath = new URL('scripts/integration.bundle.js', assetsUrl).href;
+
   window.SOURCEGRAPH_ASSETS_URL = assetsUrl.href;
   window.SOURCEGRAPH_URL = sourcegraphUrl;
   window.SOURCEGRAPH_INTEGRATION = 'gitlab-integration';
-  // inject a <script> tag to fetch the main JS bundle from the Sourcegraph instance
-  const script = document.createElement('script');
-  script.type = 'application/javascript';
-  script.src = new URL('scripts/integration.bundle.js', assetsUrl).href;
-  script.defer = true;
-  document.head.appendChild(script);
+
+  loadScript(scriptPath);
 }

app/controllers/concerns/sourcegraph_gon.rb

+module SourcegraphGon
+  extend ActiveSupport::Concern
+
+  def push_sourcegraph_gon
+    return unless enabled?
+
+    gon.push({
+      sourcegraph_enabled: true,
+      sourcegraph_url: Gitlab::CurrentSettings.sourcegraph_url
+    })
+  end
+
+  private 
+
+  def enabled?
+    current_user&.sourcegraph_enabled && project_enabled?
+  end
+
+  def project_enabled?
+    return false unless project && Gitlab::Sourcegraph.feature_enabled?(project)
+    return project.public? if Gitlab::CurrentSettings.sourcegraph_public_only
+
+    true
+  end
+
+  def project
+    @target_project || @project  
+  end
+end

app/controllers/profiles/preferences_controller.rb

@@ -47,7 +47,8 @@ class Profiles::PreferencesController < Profiles::ApplicationController
       :preferred_language,
       :time_display_relative,
       :time_format_in_24h,
-      :show_whitespace_in_diffs
+      :show_whitespace_in_diffs,
+      :sourcegraph_enabled
     ]
   end
 end

app/controllers/projects/application_controller.rb

@@ -4,10 +4,12 @@ class Projects::ApplicationController < ApplicationController
   include CookiesHelper
   include RoutableActions
   include ChecksCollaboration
+  include SourcegraphGon
 
   skip_before_action :authenticate_user!
   before_action :project
   before_action :repository
+  before_action :push_sourcegraph_gon
   layout 'project'
 
   helper_method :repository, :can_collaborate_with_project?, :user_access

app/helpers/application_settings_helper.rb

@@ -261,6 +261,7 @@ module ApplicationSettingsHelper
       :signup_enabled,
       :sourcegraph_enabled,
       :sourcegraph_url,
+      :sourcegraph_public_only,
       :terminal_max_session_time,
       :terms,
       :throttle_authenticated_api_enabled,

app/helpers/sourcegraph_helper.rb

+# frozen_string_literal: true
+
+module SourcegraphHelper
+  def sourcegraph_help_message
+    return unless Gitlab::CurrentSettings.sourcegraph_enabled
+
+    if Gitlab::Sourcegraph.feature_conditional?
+      _("This feature is experimental and has been limited to only certain projects.")
+    elsif Gitlab::CurrentSettings.sourcegraph_public_only
+      _("This feature is experimental and also limited to only public projects.")
+    else
+      _("This feature is experimental.")
+    end
+  end
+end

app/models/application_setting.rb

@@ -347,6 +347,10 @@ class ApplicationSetting < ApplicationRecord
   end
   after_commit :expire_performance_bar_allowed_user_ids_cache, if: -> { previous_changes.key?('performance_bar_allowed_group_id') }
 
+  def sourcegraph_enabled
+    super && Gitlab::Sourcegraph.feature_available?
+  end
+
   def self.create_from_defaults
     transaction(requires_new: true) do
       super

app/models/application_setting_implementation.rb

@@ -104,6 +104,7 @@ module ApplicationSettingImplementation
         signup_enabled: Settings.gitlab['signup_enabled'],
         sourcegraph_enabled: false,
         sourcegraph_url: nil,
+        sourcegraph_public_only: true,
         terminal_max_session_time: 0,
         throttle_authenticated_api_enabled: false,
         throttle_authenticated_api_period_in_seconds: 3600,

app/models/user.rb

@@ -240,6 +240,7 @@ class User < ApplicationRecord
   delegate :time_display_relative, :time_display_relative=, to: :user_preference
   delegate :time_format_in_24h, :time_format_in_24h=, to: :user_preference
   delegate :show_whitespace_in_diffs, :show_whitespace_in_diffs=, to: :user_preference
+  delegate :sourcegraph_enabled, :sourcegraph_enabled=, to: :user_preference
   delegate :setup_for_company, :setup_for_company=, to: :user_preference
 
   accepts_nested_attributes_for :user_preference, update_only: true

app/models/user_preference.rb

@@ -24,6 +24,10 @@ class UserPreference < ApplicationRecord
     end
   end
 
+  def sourcegraph_enabled
+    super && Gitlab::CurrentSettings.sourcegraph_enabled
+  end
+
   def set_notes_filter(filter_id, issuable)
     # No need to update the column if the value is already set.
     if filter_id && NOTES_FILTERS.value?(filter_id)

app/views/admin/application_settings/_sourcegraph.html.haml

+- return unless Gitlab::Sourcegraph.feature_available?
 - expanded = integration_expanded?('sourcegraph_')
+
 %section.settings.as-sourcegraph.no-animate#js-sourcegraph-settings{ class: ('expanded' if expanded) }
   .settings-header
     %h4
@@ -19,7 +21,12 @@
             = f.label :sourcegraph_enabled, _('Enable Sourcegraph'), class: 'form-check-label'
         .form-group
           = f.label :sourcegraph_url, _('Sourcegraph URL'), class: 'label-bold'
-          = f.text_field :sourcegraph_url, class: 'form-control', placeholder: 'https://example.sourcegraph.com'
+          = f.text_field :sourcegraph_url, class: 'form-control', placeholder: 'e.g. https://sourcegraph.example.com'
+          .form-text.text-muted
+            = _('Add %{link} code intelligence to your GitLab instance code views and merge requests.').html_safe % { link: link_to('Sourcegraph', 'https://sourcegraph.com/', target: '_blank') }
+        .form-group
+          = f.label :sourcegraph_public_only, _('Scope'), class: 'label-bold'
+          = f.select :sourcegraph_public_only, [[_('All projects'), false], [_('Public projects only'), true]], {}, class: 'form-control'
           .form-text.text-muted
-            = _('Add %{link} code intelligence to your GitLab instance code views and pull requests.').html_safe % { link: link_to('Sourcegraph', 'https://sourcegraph.com/', target: '_blank') }
+            = _('Configure which projects should allow requests to Sourcegraph.')
       = f.submit _('Save changes'), class: 'btn btn-success'

app/views/profiles/preferences/_sourcegraph.html.haml

+- return unless Gitlab::CurrentSettings.sourcegraph_enabled
+- sourcegraph_url = Gitlab::CurrentSettings.sourcegraph_url
+
+.col-sm-12
+  %hr
+
+.col-lg-4.profile-settings-sidebar
+  %h4.prepend-top-0
+    = _('Integrations')
+  %p
+    = _('Customize integrations with third party services.')
+    = succeed '.' do
+      = link_to _('Learn more'), help_page_path('user/profile/third-party.md', anchor: 'localization'), target: '_blank'
+.col-lg-8
+  %label.label-bold
+    = s_('Preferences|Sourcegraph')
+  = link_to icon('question-circle'), help_page_path('user/profile/sourcegraph.md'), target: '_blank'
+  .form-group.form-check
+    = f.check_box :sourcegraph_enabled, class: 'form-check-input'
+    = f.label :sourcegraph_enabled, class: 'form-check-label' do
+      - link_start = '<a href="%{url}">'.html_safe % { url: sourcegraph_url }
+      - link_end = '</a>'.html_safe
+      = s_('Preferences|Enable integrated code intelligence on code views, %{link_start}powered by Sourcegraph%{link_end}.').html_safe % { link_start: link_start, link_end: link_end }
+    .form-text.text-muted
+      = sourcegraph_help_message

app/views/profiles/preferences/show.html.haml

@@ -111,6 +111,9 @@
             = time_display_label
           .form-text.text-muted
             = s_('Preferences|For example: 30 mins ago.')
+
+  = render 'sourcegraph', f: f
+
   .col-lg-4.profile-settings-sidebar
   .col-lg-8
     .form-group

db/migrate/20191107173446_add_sourcegraph_admin_and_user_preferences.rb

+# frozen_string_literal: true
+
+class AddSourcegraphAdminAndUserPreferences < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default(:application_settings, :sourcegraph_public_only, :boolean, default: true)
+    add_column(:user_preferences, :sourcegraph_enabled, :boolean)
+  end
+
+  def down
+    remove_column(:application_settings, :sourcegraph_public_only)
+    remove_column(:user_preferences, :sourcegraph_enabled)
+  end
+end

db/schema.rb

@@ -354,6 +354,7 @@ ActiveRecord::Schema.define(version: 2019_11_12_232338) do
     t.string "default_ci_config_path", limit: 255
     t.boolean "sourcegraph_enabled", default: false, null: false
     t.string "sourcegraph_url", limit: 255
+    t.boolean "sourcegraph_public_only", default: true, null: false
     t.index ["custom_project_templates_group_id"], name: "index_application_settings_on_custom_project_templates_group_id"
     t.index ["file_template_project_id"], name: "index_application_settings_on_file_template_project_id"
     t.index ["instance_administration_project_id"], name: "index_applicationsettings_on_instance_administration_project_id"
@@ -3773,6 +3774,7 @@ ActiveRecord::Schema.define(version: 2019_11_12_232338) do
     t.boolean "time_format_in_24h"
     t.string "projects_sort", limit: 64
     t.boolean "show_whitespace_in_diffs", default: true, null: false
+    t.boolean "sourcegraph_enabled"
     t.boolean "setup_for_company"
     t.index ["user_id"], name: "index_user_preferences_on_user_id", unique: true
   end

lib/gitlab/gon_helper.rb

@@ -32,9 +32,6 @@ module Gitlab
       gon.first_day_of_week      = current_user&.first_day_of_week || Gitlab::CurrentSettings.first_day_of_week
       gon.ee                     = Gitlab.ee?
 
-      gon.sourcegraph_enabled    = Gitlab::CurrentSettings.sourcegraph_enabled
-      gon.sourcegraph_url        = Gitlab::CurrentSettings.sourcegraph_url
-
       if current_user
         gon.current_user_id = current_user.id
         gon.current_username = current_user.username

lib/gitlab/sourcegraph.rb

+# frozen_string_literal: true
+
+module Gitlab
+  class Sourcegraph
+    class << self
+      def feature_conditional?
+        feature.conditional?
+      end
+
+      def feature_available?
+        # The sourcegraph_bundle feature could be conditionally applied, so check if `!off?`
+        !feature.off?
+      end
+
+      def feature_enabled?(thing = true)
+        feature.enabled?(thing)
+      end
+
+      private
+
+      def feature
+        Feature.get(:sourcegraph)
+      end
+    end
+  end
+end

spec/requests/api/settings_spec.rb

@@ -46,6 +46,7 @@ describe API::Settings, 'Settings' do
         storages = Gitlab.config.repositories.storages
                      .merge({ 'custom' => 'tmp/tests/custom_repositories' })
         allow(Gitlab.config.repositories).to receive(:storages).and_return(storages)
+        Feature.get(:sourcegraph).enable
       end
 
       it "updates application settings" do
@@ -60,6 +61,7 @@ describe API::Settings, 'Settings' do
             plantuml_url: 'http://plantuml.example.com',
             sourcegraph_enabled: true,
             sourcegraph_url: 'https://sourcegraph.com',
+            sourcegraph_public_only: false,
             default_snippet_visibility: 'internal',
             restricted_visibility_levels: ['public'],
             default_artifacts_expire_in: '2 days',
@@ -94,6 +96,7 @@ describe API::Settings, 'Settings' do
         expect(json_response['plantuml_url']).to eq('http://plantuml.example.com')
         expect(json_response['sourcegraph_enabled']).to be_truthy
         expect(json_response['sourcegraph_url']).to eq('https://sourcegraph.com')
+        expect(json_response['sourcegraph_public_only']).to eq(false)
         expect(json_response['default_snippet_visibility']).to eq('internal')
         expect(json_response['restricted_visibility_levels']).to eq(['public'])
         expect(json_response['default_artifacts_expire_in']).to eq('2 days')

spec/views/profiles/preferences/show.html.haml_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'profiles/preferences/show' do
+  using RSpec::Parameterized::TableSyntax
+
+  let(:user) { create(:user) }
+
+  before do
+    assign(:user, user)
+    allow(controller).to receive(:current_user).and_return(user)
+  end
+
+  context 'sourcegraph' do
+    def have_sourcegraph_field(*args)
+      have_field('user_sourcegraph_enabled', *args)
+    end
+
+    def have_integrations_section
+      have_css('.profile-settings-sidebar', { text: 'Integrations' })
+    end
+
+    before do
+      # Can't use stub_feature_flags because we use Feature.get to check if conditinally applied
+      Feature.get(:sourcegraph).enable sourcegraph_feature
+      Gitlab::CurrentSettings.sourcegraph_enabled = sourcegraph_enabled
+    end
+
+    context 'when not fully enabled' do
+      where(:feature, :admin_enabled) do
+        false | false
+        false | true
+        true | false
+      end
+
+      with_them do
+        let(:sourcegraph_feature) { feature }
+        let(:sourcegraph_enabled) { admin_enabled }
+
+        before do
+          render
+        end
+
+        it 'does not display sourcegraph field' do
+          expect(rendered).not_to have_sourcegraph_field
+        end
+        
+        it 'does not display integrations settings' do
+          expect(rendered).not_to have_integrations_section
+        end
+      end
+    end
+
+    context 'when fully enabled' do
+      let(:sourcegraph_feature) { true }
+      let(:sourcegraph_enabled) { true }
+
+      before do
+        render
+      end
+
+      it 'displays the sourcegraph field' do
+        expect(rendered).to have_sourcegraph_field
+      end
+
+      it 'displays the integrations section' do
+        expect(rendered).to have_integrations_section
+      end
+    end
+  end
+end