Port `read_cross_project` ability from EE

app/controllers/application_controller.rb

@@ -126,10 +126,15 @@ class ApplicationController < ActionController::Base
     Ability.allowed?(object, action, subject)
   end
 
-  def access_denied!
+  def access_denied!(message = nil)
     respond_to do |format|
-      format.json { head :not_found }
-      format.any { render "errors/access_denied", layout: "errors", status: 404 }
+      format.any { head :not_found }
+      format.html do
+        render "errors/access_denied",
+               layout: "errors",
+               status: 404,
+               locals: { message: message }
+      end
     end
   end
 

app/controllers/boards/issues_controller.rb

@@ -55,7 +55,7 @@ module Boards
     end
 
     def issue
-      @issue ||= issues_finder.execute.find(params[:id])
+      @issue ||= issues_finder.find(params[:id])
     end
 
     def filter_params

app/controllers/concerns/controller_with_cross_project_access_check.rb

+module ControllerWithCrossProjectAccessCheck
+  extend ActiveSupport::Concern
+
+  included do
+    extend Gitlab::CrossProjectAccess::ClassMethods
+    before_action :cross_project_check
+  end
+
+  def cross_project_check
+    if Gitlab::CrossProjectAccess.find_check(self)&.should_run?(self)
+      authorize_cross_project_page!
+    end
+  end
+
+  def authorize_cross_project_page!
+    return if can?(current_user, :read_cross_project)
+
+    rejection_message = _(
+      "This page is unavailable because you are not allowed to read information "\
+      "across multiple projects."
+    )
+    access_denied!(rejection_message)
+  end
+end

app/controllers/concerns/routable_actions.rb

@@ -3,16 +3,20 @@ module RoutableActions
 
   def find_routable!(routable_klass, requested_full_path, extra_authorization_proc: nil)
     routable = routable_klass.find_by_full_path(requested_full_path, follow_redirects: request.get?)
-
     if routable_authorized?(routable, extra_authorization_proc)
       ensure_canonical_path(routable, requested_full_path)
       routable
     else
-      route_not_found
+      handle_not_found_or_authorized(routable)
       nil
     end
   end
 
+  # This is overridden in gitlab-ee.
+  def handle_not_found_or_authorized(_routable)
+    route_not_found
+  end
+
   def routable_authorized?(routable, extra_authorization_proc)
     action = :"read_#{routable.class.to_s.underscore}"
     return false unless can?(current_user, action, routable)

app/controllers/dashboard/application_controller.rb

 class Dashboard::ApplicationController < ApplicationController
+  include ControllerWithCrossProjectAccessCheck
+
   layout 'dashboard'
 
+  requires_cross_project_access
+
   private
 
   def projects

app/controllers/dashboard/groups_controller.rb

 class Dashboard::GroupsController < Dashboard::ApplicationController
   include GroupTree
 
+  skip_cross_project_access_check :index
+
   def index
     groups = GroupsFinder.new(current_user, all_available: false).execute
     render_group_tree(groups)

app/controllers/dashboard/projects_controller.rb

@@ -4,6 +4,7 @@ class Dashboard::ProjectsController < Dashboard::ApplicationController
 
   before_action :set_non_archived_param
   before_action :default_sorting
+  skip_cross_project_access_check :index, :starred
 
   def index
     @projects = load_projects(params.merge(non_public: true)).page(params[:page])

app/controllers/dashboard/snippets_controller.rb

 class Dashboard::SnippetsController < Dashboard::ApplicationController
+  skip_cross_project_access_check :index
+
   def index
     @snippets = SnippetsFinder.new(
       current_user,

app/controllers/groups/application_controller.rb

 class Groups::ApplicationController < ApplicationController
   include RoutableActions
+  include ControllerWithCrossProjectAccessCheck
 
   layout 'group'
 
   skip_before_action :authenticate_user!
   before_action :group
+  requires_cross_project_access
 
   private
 

app/controllers/groups/avatars_controller.rb

 class Groups::AvatarsController < Groups::ApplicationController
   before_action :authorize_admin_group!
 
+  skip_cross_project_access_check :destroy
+
   def destroy
     @group.remove_avatar!
     @group.save

app/controllers/groups/children_controller.rb

 module Groups
   class ChildrenController < Groups::ApplicationController
     before_action :group
+    skip_cross_project_access_check :index
 
     def index
       parent = if params[:parent_id].present?

app/controllers/groups/group_members_controller.rb

@@ -6,6 +6,10 @@ class Groups::GroupMembersController < Groups::ApplicationController
   # Authorize
   before_action :authorize_admin_group_member!, except: [:index, :leave, :request_access]
 
+  skip_cross_project_access_check :index, :create, :update, :destroy, :request_access,
+                                  :approve_access_request, :leave, :resend_invite,
+                                  :override
+
   def index
     @sort = params[:sort].presence || sort_value_name
     @project = @group.projects.find(params[:project_id]) if params[:project_id]

app/controllers/groups/settings/ci_cd_controller.rb

 module Groups
   module Settings
     class CiCdController < Groups::ApplicationController
+      skip_cross_project_access_check :show
       before_action :authorize_admin_pipeline!
 
       def show

app/controllers/groups/variables_controller.rb

@@ -2,6 +2,8 @@ module Groups
   class VariablesController < Groups::ApplicationController
     before_action :authorize_admin_build!
 
+    skip_cross_project_access_check :show, :update
+
     def show
       respond_to do |format|
         format.json do

app/controllers/groups_controller.rb

@@ -19,6 +19,12 @@ class GroupsController < Groups::ApplicationController
 
   before_action :user_actions, only: [:show, :subgroups]
 
+  skip_cross_project_access_check :index, :new, :create, :edit, :update,
+                                  :destroy, :projects
+  # When loading show as an atom feed, we render events that could leak cross
+  # project information
+  skip_cross_project_access_check :show, if: -> { request.format.html? }
+
   layout :determine_layout
 
   def index

app/controllers/oauth/applications_controller.rb

 class Oauth::ApplicationsController < Doorkeeper::ApplicationsController
   include Gitlab::GonHelper
+  include Gitlab::Allowable
   include PageLayoutHelper
   include OauthApplications
 
@@ -8,6 +9,8 @@ class Oauth::ApplicationsController < Doorkeeper::ApplicationsController
   before_action :add_gon_variables
   before_action :load_scopes, only: [:index, :create, :edit]
 
+  helper_method :can?
+
   layout 'profile'
 
   def index

app/controllers/projects/autocomplete_sources_controller.rb

@@ -34,9 +34,9 @@ class Projects::AutocompleteSourcesController < Projects::ApplicationController
   def target
     case params[:type]&.downcase
     when 'issue'
-      IssuesFinder.new(current_user, project_id: @project.id).execute.find_by(iid: params[:type_id])
+      IssuesFinder.new(current_user, project_id: @project.id).find_by(iid: params[:type_id])
     when 'mergerequest'
-      MergeRequestsFinder.new(current_user, project_id: @project.id).execute.find_by(iid: params[:type_id])
+      MergeRequestsFinder.new(current_user, project_id: @project.id).find_by(iid: params[:type_id])
     when 'commit'
       @project.commit(params[:type_id])
     end

app/controllers/projects/blob_controller.rb

@@ -133,7 +133,7 @@ class Projects::BlobController < Projects::ApplicationController
   end
 
   def after_edit_path
-    from_merge_request = MergeRequestsFinder.new(current_user, project_id: @project.id).execute.find_by(iid: params[:from_merge_request_iid])
+    from_merge_request = MergeRequestsFinder.new(current_user, project_id: @project.id).find_by(iid: params[:from_merge_request_iid])
     if from_merge_request && @branch_name == @ref
       diffs_project_merge_request_path(from_merge_request.target_project, from_merge_request) +
         "##{hexdigest(@path)}"

app/controllers/projects/merge_requests/creations_controller.rb

@@ -75,7 +75,7 @@ class Projects::MergeRequests::CreationsController < Projects::MergeRequests::Ap
   def branch_to
     @target_project = selected_target_project
 
-    if params[:ref].present?
+    if @target_project && params[:ref].present?
       @ref = params[:ref]
       @commit = @target_project.commit(Gitlab::Git::BRANCH_REF_PREFIX + @ref)
     end
@@ -85,7 +85,7 @@ class Projects::MergeRequests::CreationsController < Projects::MergeRequests::Ap
 
   def update_branches
     @target_project = selected_target_project
-    @target_branches = @target_project.repository.branch_names
+    @target_branches = @target_project ? @target_project.repository.branch_names : []
 
     render layout: false
   end
@@ -121,7 +121,7 @@ class Projects::MergeRequests::CreationsController < Projects::MergeRequests::Ap
       @project
     elsif params[:target_project_id].present?
       MergeRequestTargetProjectFinder.new(current_user: current_user, source_project: @project)
-        .execute.find(params[:target_project_id])
+        .find_by(id: params[:target_project_id])
     else
       @project.forked_from_project
     end

app/controllers/search_controller.rb

 class SearchController < ApplicationController
-  skip_before_action :authenticate_user!
-
+  include ControllerWithCrossProjectAccessCheck
   include SearchHelper
   include RendersCommits
 
+  skip_before_action :authenticate_user!
+  requires_cross_project_access if: -> do
+    search_term_present = params[:search].present? || params[:term].present?
+    search_term_present && !params[:project_id].present?
+  end
+
   layout 'search'
 
   def show

app/controllers/users_controller.rb

 class UsersController < ApplicationController
   include RoutableActions
   include RendersMemberAccess
+  include ControllerWithCrossProjectAccessCheck
+
+  requires_cross_project_access show: false,
+                                groups: false,
+                                projects: false,
+                                contributed: false,
+                                snippets: true,
+                                calendar: false,
+                                calendar_activities: true
 
   skip_before_action :authenticate_user!
   before_action :user, except: [:exists]
@@ -103,12 +112,7 @@ class UsersController < ApplicationController
   end
 
   def load_events
-    # Get user activity feed for projects common for both users
-    @events = user.recent_events
-      .merge(projects_for_current_user)
-      .references(:project)
-      .with_associations
-      .limit_recent(20, params[:offset])
+    @events = UserRecentEventsFinder.new(current_user, user, params).execute
 
     Events::RenderService.new(current_user).execute(@events, atom_request: request.format.atom?)
   end
@@ -141,10 +145,6 @@ class UsersController < ApplicationController
     ).execute.page(params[:page])
   end
 
-  def projects_for_current_user
-    ProjectsFinder.new(current_user: current_user).execute
-  end
-
   def build_canonical_path(user)
     url_for(params.merge(username: user.to_param))
   end

app/finders/concerns/finder_methods.rb

+module FinderMethods
+  def find_by!(*args)
+    raise_not_found_unless_authorized execute.find_by!(*args)
+  end
+
+  def find_by(*args)
+    if_authorized execute.find_by(*args)
+  end
+
+  def find(*args)
+    raise_not_found_unless_authorized model.find(*args)
+  end
+
+  private
+
+  def raise_not_found_unless_authorized(result)
+    result = if_authorized(result)
+
+    raise ActiveRecord::RecordNotFound.new("Couldn't find #{model}") unless result
+
+    result
+  end
+
+  def if_authorized(result)
+    # Return the result if the finder does not perform authorization checks.
+    # this is currently the case in the `MilestoneFinder`
+    return result unless respond_to?(:current_user)
+
+    if can_read_object?(result)
+      result
+    else
+      nil
+    end
+  end
+
+  def can_read_object?(object)
+    # When there's no policy, we'll allow the read, this is for example the case
+    # for Todos
+    return true unless DeclarativePolicy.has_policy?(object)
+
+    model_name = object&.model_name || model.model_name
+
+    Ability.allowed?(current_user, :"read_#{model_name.singular}", object)
+  end
+
+  # This fetches the model from the `ActiveRecord::Relation` but does not
+  # actually execute the query.
+  def model
+    execute.model
+  end
+end

app/finders/concerns/finder_with_cross_project_access.rb

+# Module to prepend into finders to specify wether or not the finder requires
+# cross project access
+#
+# This module depends on the finder implementing the following methods:
+#
+# - `#execute` should return an `ActiveRecord::Relation`
+# - `#current_user` the user that requires access (or nil)
+module FinderWithCrossProjectAccess
+  extend ActiveSupport::Concern
+  extend ::Gitlab::Utils::Override
+
+  prepended do
+    extend Gitlab::CrossProjectAccess::ClassMethods
+  end
+
+  override :execute
+  def execute(*args)
+    check = Gitlab::CrossProjectAccess.find_check(self)
+    original = super
+
+    return original unless check
+    return original if should_skip_cross_project_check || can_read_cross_project?
+
+    if check.should_run?(self)
+      original.model.none
+    else
+      original
+    end
+  end
+
+  # We can skip the cross project check for finding indivitual records.
+  # this would be handled by the `can?(:read_*, result)` call in `FinderMethods`
+  # itself.
+  override :find_by!
+  def find_by!(*args)
+    skip_cross_project_check { super }
+  end
+
+  override :find_by
+  def find_by(*args)
+    skip_cross_project_check { super }
+  end
+
+  override :find
+  def find(*args)
+    skip_cross_project_check { super }
+  end
+
+  private
+
+  attr_accessor :should_skip_cross_project_check
+
+  def skip_cross_project_check
+    self.should_skip_cross_project_check = true
+
+    yield
+  ensure
+    # The find could raise an `ActiveRecord::RecordNotFound`, after which we
+    # still want to re-enable the check.
+    self.should_skip_cross_project_check = false
+  end
+
+  def can_read_cross_project?
+    Ability.allowed?(current_user, :read_cross_project)
+  end
+
+  def can_read_project?(project)
+    Ability.allowed?(current_user, :read_project, project)
+  end
+end

app/finders/events_finder.rb

 class EventsFinder
+  prepend FinderMethods
+  prepend FinderWithCrossProjectAccess
   attr_reader :source, :params, :current_user
 
+  requires_cross_project_access unless: -> { source.is_a?(Project) }
+
   # Used to filter Events
   #
   # Arguments:

app/finders/issuable_finder.rb

@@ -21,8 +21,12 @@
 #     my_reaction_emoji: string
 #
 class IssuableFinder
+  prepend FinderWithCrossProjectAccess
+  include FinderMethods
   include CreatedAtFilter
 
+  requires_cross_project_access unless: -> { project? }
+
   NONE = '0'.freeze
 
   attr_accessor :current_user, :params
@@ -87,14 +91,6 @@ class IssuableFinder
     by_my_reaction_emoji(items)
   end
 
-  def find(*params)
-    execute.find(*params)
-  end
-
-  def find_by(*params)
-    execute.find_by(*params)
-  end
-
   def row_count
     Gitlab::IssuablesCountForState.new(self).for_state_or_opened(params[:state])
   end
@@ -124,10 +120,6 @@ class IssuableFinder
     counts
   end
 
-  def find_by!(*params)
-    execute.find_by!(*params)
-  end
-
   def group
     return @group if defined?(@group)
 

app/finders/labels_finder.rb

 class LabelsFinder < UnionFinder
+  prepend FinderWithCrossProjectAccess
+  include FinderMethods
   include Gitlab::Utils::StrongMemoize
 
+  requires_cross_project_access unless: -> { project? }
+
   def initialize(current_user, params = {})
     @current_user = current_user
     @params = params

app/finders/merge_request_target_project_finder.rb

 class MergeRequestTargetProjectFinder
+  include FinderMethods
+
   attr_reader :current_user, :source_project
 
   def initialize(current_user: nil, source_project:)

app/finders/milestones_finder.rb

@@ -8,6 +8,8 @@
 #   state - filters by state.
 
 class MilestonesFinder
+  include FinderMethods
+
   attr_reader :params, :project_ids, :group_ids
 
   def initialize(params = {})

app/finders/snippets_finder.rb

@@ -13,7 +13,9 @@
 # params are optional
 class SnippetsFinder < UnionFinder
   include Gitlab::Allowable
-  attr_accessor :current_user, :params, :project
+  include FinderMethods
+
+  attr_accessor :current_user, :project, :params
 
   def initialize(current_user, params = {})
     @current_user = current_user
@@ -52,10 +54,14 @@ class SnippetsFinder < UnionFinder
   end
 
   def authorized_snippets
-    Snippet.where(feature_available_projects.or(not_project_related)).public_or_visible_to_user(current_user)
+    Snippet.where(feature_available_projects.or(not_project_related))
+      .public_or_visible_to_user(current_user)
   end
 
   def feature_available_projects
+    # Don't return any project related snippets if the user cannot read cross project
+    return table[:id].eq(nil) unless Ability.allowed?(current_user, :read_cross_project)
+
     projects = Project.public_or_visible_to_user(current_user, use_where_in: false) do |part|
       part.with_feature_available_for_user(:snippets, current_user)
     end.select(:id)

app/finders/todos_finder.rb

@@ -13,6 +13,11 @@
 #
 
 class TodosFinder
+  prepend FinderWithCrossProjectAccess
+  include FinderMethods
+
+  requires_cross_project_access unless: -> { project? }
+
   NONE = '0'.freeze
 
   attr_accessor :current_user, :params

app/finders/user_recent_events_finder.rb

+# Get user activity feed for projects common for a user and a logged in user
+#
+# - current_user: The user viewing the events
+# - user: The user for which to load the events
+# - params:
+#   - offset: The page of events to return
+class UserRecentEventsFinder
+  prepend FinderWithCrossProjectAccess
+  include FinderMethods
+
+  requires_cross_project_access
+
+  attr_reader :current_user, :target_user, :params
+
+  def initialize(current_user, target_user, params = {})
+    @current_user = current_user
+    @target_user = target_user
+    @params = params
+  end
+
+  def execute
+    target_user
+      .recent_events
+      .merge(projects_for_current_user)
+      .references(:project)
+      .with_associations
+      .limit_recent(20, params[:offset])
+  end
+
+  def projects_for_current_user
+    ProjectsFinder.new(current_user: current_user).execute
+  end
+end

app/helpers/dashboard_helper.rb

@@ -6,4 +6,28 @@ module DashboardHelper
   def assigned_mrs_dashboard_path
     merge_requests_dashboard_path(assignee_id: current_user.id)
   end
+
+  def dashboard_nav_links
+    @dashboard_nav_links ||= get_dashboard_nav_links
+  end
+
+  def dashboard_nav_link?(link)
+    dashboard_nav_links.include?(link)
+  end
+
+  def any_dashboard_nav_link?(links)
+    links.any? { |link| dashboard_nav_link?(link) }
+  end
+
+  private
+
+  def get_dashboard_nav_links
+    links = [:projects, :groups, :snippets]
+
+    if can?(current_user, :read_cross_project)
+      links += [:activity, :milestones]
+    end
+
+    links
+  end
 end

app/helpers/explore_helper.rb

@@ -25,8 +25,24 @@ module ExploreHelper
     controller.class.name.split("::").first == "Explore"
   end
 
+  def explore_nav_links
+    @explore_nav_links ||= get_explore_nav_links
+  end
+
+  def explore_nav_link?(link)
+    explore_nav_links.include?(link)
+  end
+
+  def any_explore_nav_link?(links)
+    links.any? { |link| explore_nav_link?(link) }
+  end
+
   private
 
+  def get_explore_nav_links
+    [:projects, :groups, :snippets]
+  end
+
   def request_path_with_options(options = {})
     request.path + "?#{options.to_param}"
   end

app/helpers/groups_helper.rb

@@ -3,6 +3,14 @@ module GroupsHelper
     %w[groups#projects groups#edit ci_cd#show ldap_group_links#index hooks#index audit_events#index pipeline_quota#index]
   end
 
+  def group_sidebar_links
+    @group_sidebar_links ||= get_group_sidebar_links
+  end
+
+  def group_sidebar_link?(link)
+    group_sidebar_links.include?(link)
+  end
+
   def can_change_group_visibility_level?(group)
     can?(current_user, :change_visibility_level, group)
   end
@@ -107,6 +115,20 @@ module GroupsHelper
 
   private
 
+  def get_group_sidebar_links
+    links = [:overview, :group_members]
+
+    if can?(current_user, :read_cross_project)
+      links += [:activity, :issues, :labels, :milestones, :merge_requests]
+    end
+
+    if can?(current_user, :admin_group, @group)
+      links << :settings
+    end
+
+    links
+  end
+
   def group_title_link(group, hidable: false, show_avatar: false, for_dropdown: false)
     link_to(group_path(group), class: "group-path #{'breadcrumb-item-text' unless for_dropdown} js-breadcrumb-item-text #{'hidable' if hidable}") do
       output =

app/helpers/issues_helper.rb

@@ -47,27 +47,6 @@ module IssuesHelper
     end
   end
 
-  def milestone_options(object)
-    milestones = object.project.milestones.active.reorder(due_date: :asc, title: :asc).to_a
-    milestones.unshift(object.milestone) if object.milestone.present? && object.milestone.closed?
-    milestones.unshift(Milestone::None)
-
-    options_from_collection_for_select(milestones, 'id', 'title', object.milestone_id)
-  end
-
-  def project_options(issuable, current_user, ability: :read_project)
-    projects = current_user.authorized_projects.order_id_desc
-    projects = projects.select do |project|
-      current_user.can?(ability, project)
-    end
-
-    no_project = OpenStruct.new(id: 0, name_with_namespace: 'No project')
-    projects.unshift(no_project)
-    projects.delete(issuable.project)
-
-    options_from_collection_for_select(projects, :id, :name_with_namespace)
-  end
-
   def status_box_class(item)
     if item.try(:expired?)
       'status-box-expired'

app/helpers/nav_helper.rb

 module NavHelper
+  def header_links
+    @header_links ||= get_header_links
+  end
+
+  def header_link?(link)
+    header_links.include?(link)
+  end
+
   def page_with_sidebar_class
     class_name = page_gutter_class
     class_name << 'page-with-contextual-sidebar' if defined?(@left_sidebar) && @left_sidebar
@@ -38,4 +46,28 @@ module NavHelper
 
     class_names
   end
+
+  private
+
+  def get_header_links
+    links = if current_user
+              [:user_dropdown]
+            else
+              [:sign_in]
+            end
+
+    if can?(current_user, :read_cross_project)
+      links += [:issues, :merge_requests, :todos] if current_user.present?
+    end
+
+    if @project&.persisted? || can?(current_user, :read_cross_project)
+      links << :search
+    end
+
+    if session[:impersonator_id]
+      links << :admin_impersonation
+    end
+
+    links
+  end
 end

app/helpers/projects_helper.rb

@@ -213,6 +213,7 @@ module ProjectsHelper
       controller.controller_name,
       controller.action_name,
       Gitlab::CurrentSettings.cache_key,
+      "cross-project:#{can?(current_user, :read_cross_project)}",
       'v2.5'
     ]
 
@@ -608,4 +609,8 @@ module ProjectsHelper
 
     project_find_file_path(@project, ref)
   end
+
+  def can_show_last_commit_in_list?(project)
+    can?(current_user, :read_cross_project) && project.commit
+  end
 end

app/helpers/users_helper.rb

@@ -14,4 +14,18 @@ module UsersHelper
       content_tag(:strong) { user.unconfirmed_email } + h('.') +
       content_tag(:p) { confirmation_link }
   end
+
+  def profile_tabs
+    @profile_tabs ||= get_profile_tabs
+  end
+
+  def profile_tab?(tab)
+    profile_tabs.include?(tab)
+  end
+
+  private
+
+  def get_profile_tabs
+    [:activity, :groups, :contributed, :projects, :snippets]
+  end
 end

app/models/ability.rb

@@ -22,12 +22,30 @@ class Ability
     #
     # issues - The issues to reduce down to those readable by the user.
     # user - The User for which to check the issues
-    def issues_readable_by_user(issues, user = nil)
+    # filters - A hash of abilities and filters to apply if the user lacks this
+    #           ability
+    def issues_readable_by_user(issues, user = nil, filters: {})
+      issues = apply_filters_if_needed(issues, user, filters)
+
       DeclarativePolicy.user_scope do
         issues.select { |issue| issue.visible_to_user?(user) }
       end
     end
 
+    # Returns an Array of MergeRequests that can be read by the given user.
+    #
+    # merge_requests - MRs out of which to collect mr's readable by the user.
+    # user - The User for which to check the merge_requests
+    # filters - A hash of abilities and filters to apply if the user lacks this
+    #           ability
+    def merge_requests_readable_by_user(merge_requests, user = nil, filters: {})
+      merge_requests = apply_filters_if_needed(merge_requests, user, filters)
+
+      DeclarativePolicy.user_scope do
+        merge_requests.select { |mr| allowed?(user, :read_merge_request, mr) }
+      end
+    end
+
     def can_edit_note?(user, note)
       allowed?(user, :edit_note, note)
     end
@@ -53,5 +71,15 @@ class Ability
       cache = RequestStore.active? ? RequestStore : {}
       DeclarativePolicy.policy_for(user, subject, cache: cache)
     end
+
+    private
+
+    def apply_filters_if_needed(elements, user, filters)
+      filters.each do |ability, filter|
+        elements = filter.call(elements) unless allowed?(user, ability)
+      end
+
+      elements
+    end
   end
 end

app/models/concerns/protected_ref_access.rb

@@ -35,6 +35,7 @@ module ProtectedRefAccess
   def check_access(user)
     return true if user.admin?
 
+    user.can?(:push_code, project) &&
       project.team.max_member_access(user.id) >= access_level
   end
 end

app/models/issue.rb

@@ -159,7 +159,18 @@ class Issue < ActiveRecord::Base
       object.all_references(current_user, extractor: ext)
     end
 
-    ext.merge_requests.sort_by(&:iid)
+    merge_requests = ext.merge_requests.sort_by(&:iid)
+
+    cross_project_filter = -> (merge_requests) do
+      merge_requests.select { |mr| mr.target_project == project }
+    end
+
+    Ability.merge_requests_readable_by_user(
+      merge_requests, current_user,
+      filters: {
+        read_cross_project: cross_project_filter
+      }
+    )
   end
 
   # All branches containing the current issue's ID, except for

app/models/notification_recipient.rb

@@ -85,6 +85,7 @@ class NotificationRecipient
       return false unless user.can?(:receive_notifications)
       return true if @skip_read_ability
 
+      return false if @target && !user.can?(:read_cross_project)
       return false if @project && !user.can?(:read_project, @project)
 
       return true unless read_ability

app/models/project.rb

@@ -1036,6 +1036,9 @@ class Project < ActiveRecord::Base
   end
 
   def user_can_push_to_empty_repo?(user)
+    return false unless empty_repo?
+    return false unless Ability.allowed?(user, :push_code, self)
+
     !ProtectedBranch.default_branch_protected? || team.max_member_access(user.id) > Gitlab::Access::DEVELOPER
   end
 

app/policies/base_policy.rb

@@ -15,4 +15,7 @@ class BasePolicy < DeclarativePolicy::Base
   condition(:restricted_public_level, scope: :global) do
     Gitlab::CurrentSettings.current_application_settings.restricted_visibility_levels.include?(Gitlab::VisibilityLevel::PUBLIC)
   end
+
+  # This is prevented in some cases in `gitlab-ee`
+  rule { default }.enable :read_cross_project
 end

app/policies/issuable_policy.rb

@@ -3,6 +3,19 @@ class IssuablePolicy < BasePolicy
 
   condition(:locked, scope: :subject, score: 0) { @subject.discussion_locked? }
 
+  # We aren't checking `:read_issue` or `:read_merge_request` in this case
+  # because it could be possible for a user to see an issuable-iid
+  # (`:read_issue_iid` or `:read_merge_request_iid`) but then wouldn't be allowed
+  # to read the actual issue after a more expensive `:read_issue` check.
+  #
+  # `:read_issue` & `:read_issue_iid` could diverge in gitlab-ee.
+  condition(:visible_to_user, score: 4) do
+    Project.where(id: @subject.project)
+      .public_or_visible_to_user(@user)
+      .with_feature_available_for_user(@subject, @user)
+      .any?
+  end
+
   condition(:is_project_member) { @user && @subject.project && @subject.project.team.member?(@user) }
 
   desc "User is the assignee or author"

app/policies/issue_policy.rb

@@ -13,7 +13,10 @@ class IssuePolicy < IssuablePolicy
 
   rule { confidential & ~can_read_confidential }.policy do
     prevent :read_issue
+    prevent :read_issue_iid
     prevent :update_issue
     prevent :admin_issue
   end
+
+  rule { can?(:read_issue) | visible_to_user }.enable :read_issue_iid
 end

app/policies/merge_request_policy.rb

 class MergeRequestPolicy < IssuablePolicy
-  # pass
+  rule { can?(:read_merge_request) | visible_to_user }.enable :read_merge_request_iid
 end

app/policies/project_policy.rb

@@ -80,8 +80,9 @@ class ProjectPolicy < BasePolicy
   rule { reporter }.enable :reporter_access
   rule { developer }.enable :developer_access
   rule { master }.enable :master_access
+  rule { owner | admin }.enable :owner_access
 
-  rule { owner | admin }.policy do
+  rule { can?(:owner_access) }.policy do
     enable :guest_access
     enable :reporter_access
     enable :developer_access
@@ -98,11 +99,6 @@ class ProjectPolicy < BasePolicy
     enable :remove_pages
   end
 
-  rule { owner | reporter }.policy do
-    enable :build_download_code
-    enable :build_read_container_image
-  end
-
   rule { can?(:guest_access) }.policy do
     enable :read_project
     enable :read_board
@@ -121,6 +117,11 @@ class ProjectPolicy < BasePolicy
     enable :read_cycle_analytics
   end
 
+  # These abilities are not allowed to admins that are not members of the project,
+  # that's why they are defined separatly.
+  rule { guest & can?(:download_code) }.enable :build_download_code
+  rule { guest & can?(:read_container_image) }.enable :build_read_container_image
+
   rule { can?(:reporter_access) }.policy do
     enable :download_code
     enable :download_wiki_code
@@ -140,12 +141,19 @@ class ProjectPolicy < BasePolicy
     enable :read_merge_request
   end
 
+  # We define `:public_user_access` separately because there are cases in gitlab-ee
+  # where we enable or prevent it based on other coditions.
   rule { (~anonymous & public_project) | internal_access }.policy do
     enable :public_user_access
   end
 
   rule { can?(:public_user_access) }.policy do
+    enable :public_access
     enable :guest_access
+
+    enable :fork_project
+    enable :build_download_code
+    enable :build_read_container_image
     enable :request_access
   end
 
@@ -196,14 +204,6 @@ class ProjectPolicy < BasePolicy
     enable :create_cluster
   end
 
-  rule { can?(:public_user_access) }.policy do
-    enable :public_access
-
-    enable :fork_project
-    enable :build_download_code
-    enable :build_read_container_image
-  end
-
   rule { archived }.policy do
     prevent :create_merge_request
     prevent :push_code

app/serializers/group_child_entity.rb

@@ -11,9 +11,7 @@ class GroupChildEntity < Grape::Entity
   end
 
   expose :can_edit do |instance|
-    return false unless request.respond_to?(:current_user)
-
-    can?(request.current_user, "admin_#{type}", instance)
+    can_edit?
   end
 
   expose :edit_path do |instance|
@@ -83,4 +81,17 @@ class GroupChildEntity < Grape::Entity
   def markdown_description
     markdown_field(object, :description)
   end
+
+  def can_edit?
+    return false unless request.respond_to?(:current_user)
+
+    if project?
+      # Avoid checking rights for each project, as it might be expensive if the
+      # user cannot read cross project.
+      can?(request.current_user, :read_cross_project) &&
+        can?(request.current_user, :admin_project, object)
+    else
+      can?(request.current_user, :admin_group, object)
+    end
+  end
 end

app/services/issuable_base_service.rb

@@ -247,7 +247,7 @@ class IssuableBaseService < BaseService
     when 'add'
       todo_service.mark_todo(issuable, current_user)
     when 'done'
-      todo = TodosFinder.new(current_user).execute.find_by(target: issuable)
+      todo = TodosFinder.new(current_user).find_by(target: issuable)
       todo_service.mark_todos_as_done_by_ids(todo, current_user) if todo
     end
   end

app/views/errors/access_denied.html.haml

+- message = local_assigns.fetch(:message)
+
 - content_for(:title, 'Access Denied')
 %img{ :alt => "GitLab Logo", :src => image_path('logo.svg') }
   %h1
@@ -5,5 +7,9 @@
 .container
   %h3 Access Denied
   %hr
+  - if message
+    %p
+      = message
+  - else
     %p You are not allowed to access this page.
     %p Read more about project permissions #{link_to "here", help_page_path("user/permissions"), class: "vlink"}

app/views/layouts/header/_default.html.haml

@@ -20,29 +20,34 @@
         %ul.nav.navbar-nav
           - if current_user
             = render 'layouts/header/new_dropdown'
+          - if header_link?(:search)
             %li.hidden-sm.hidden-xs
               = render 'layouts/search' unless current_controller?(:search)
             %li.visible-sm-inline-block.visible-xs-inline-block
               = link_to search_path, title: 'Search', aria: { label: "Search" }, data: {toggle: 'tooltip', placement: 'bottom', container: 'body'} do
                 = sprite_icon('search', size: 16)
-          - if current_user
+
+          - if header_link?(:issues)
             = nav_link(path: 'dashboard#issues', html_options: { class: "user-counter" }) do
               = link_to assigned_issues_dashboard_path, title: 'Issues', class: 'dashboard-shortcuts-issues', aria: { label: "Issues" }, data: {toggle: 'tooltip', placement: 'bottom', container: 'body'} do
                 = sprite_icon('issues', size: 16)
                 - issues_count = assigned_issuables_count(:issues)
                 %span.badge.issues-count{ class: ('hidden' if issues_count.zero?) }
                   = number_with_delimiter(issues_count)
+          - if header_link?(:merge_requests)
             = nav_link(path: 'dashboard#merge_requests', html_options: { class: "user-counter" }) do
               = link_to assigned_mrs_dashboard_path, title: 'Merge requests', class: 'dashboard-shortcuts-merge_requests', aria: { label: "Merge requests" }, data: {toggle: 'tooltip', placement: 'bottom', container: 'body'} do
                 = sprite_icon('git-merge', size: 16)
                 - merge_requests_count = assigned_issuables_count(:merge_requests)
                 %span.badge.merge-requests-count{ class: ('hidden' if merge_requests_count.zero?) }
                   = number_with_delimiter(merge_requests_count)
+          - if header_link?(:todos)
             = nav_link(controller: 'dashboard/todos', html_options: { class: "user-counter" }) do
               = link_to dashboard_todos_path, title: 'Todos', aria: { label: "Todos" }, class: 'shortcuts-todos', data: {toggle: 'tooltip', placement: 'bottom', container: 'body'} do
                 = sprite_icon('todo-done', size: 16)
                 %span.badge.todos-count{ class: ('hidden' if todos_pending_count.zero?) }
                   = todos_count_format(todos_pending_count)
+          - if header_link?(:user_dropdown)
             %li.header-user.dropdown
               = link_to current_user, class: user_dropdown_class, data: { toggle: "dropdown" } do
                 = image_tag avatar_icon_for_user(current_user, 23), width: 23, height: 23, class: "header-user-avatar qa-user-avatar"
@@ -64,11 +69,11 @@
                   %li.divider
                   %li
                     = link_to "Sign out", destroy_user_session_path, class: "sign-out-link"
-            - if session[:impersonator_id]
+          - if header_link?(:admin_impersonation)
             %li.impersonation
               = link_to admin_impersonation_path, class: 'impersonation-btn', method: :delete, title: "Stop impersonation", aria: { label: 'Stop impersonation' }, data: { toggle: 'tooltip', placement: 'bottom', container: 'body' } do
                 = icon('user-secret')
-          - else
+          - if header_link?(:sign_in)
             %li
               %div
                 = link_to "Sign in / Register", new_session_path(:user, redirect_to_referer: 'yes'), class: 'btn btn-sign-in'

app/views/layouts/nav/_dashboard.html.haml

 %ul.list-unstyled.navbar-sub-nav
+  - if dashboard_nav_link?(:projects)
     = nav_link(path: ['root#index', 'projects#trending', 'projects#starred', 'dashboard/projects#index'], html_options: { id: 'nav-projects-dropdown', class: "home dropdown header-projects qa-projects-dropdown" }) do
       %a{ href: "#", data: { toggle: "dropdown" } }
         Projects
@@ -6,45 +7,55 @@
       .dropdown-menu.projects-dropdown-menu
         = render "layouts/nav/projects_dropdown/show"
 
+  - if dashboard_nav_link?(:groups)
     = nav_link(controller: ['dashboard/groups', 'explore/groups'], html_options: { class: "hidden-xs" }) do
       = link_to dashboard_groups_path, class: 'dashboard-shortcuts-groups qa-groups-link', title: 'Groups' do
         Groups
 
+  - if dashboard_nav_link?(:activity)
     = nav_link(path: 'dashboard#activity', html_options: { class: "visible-lg" }) do
       = link_to activity_dashboard_path, class: 'dashboard-shortcuts-activity', title: 'Activity' do
         Activity
 
+  - if dashboard_nav_link?(:milestones)
     = nav_link(controller: 'dashboard/milestones', html_options: { class: "visible-lg" }) do
       = link_to dashboard_milestones_path, class: 'dashboard-shortcuts-milestones', title: 'Milestones' do
         Milestones
 
+  - if dashboard_nav_link?(:snippets)
     = nav_link(controller: 'dashboard/snippets', html_options: { class: "visible-lg" }) do
       = link_to dashboard_snippets_path, class: 'dashboard-shortcuts-snippets', title: 'Snippets' do
         Snippets
 
+  - if any_dashboard_nav_link?([:groups, :milestones, :activity, :snippets])
     %li.header-more.dropdown.hidden-lg
       %a{ href: "#", data: { toggle: "dropdown" } }
         More
         = sprite_icon('angle-down', css_class: 'caret-down')
       .dropdown-menu
         %ul
+          - if dashboard_nav_link?(:groups)
             = nav_link(controller: ['dashboard/groups', 'explore/groups'], html_options: { class: "visible-xs" }) do
               = link_to dashboard_groups_path, class: 'dashboard-shortcuts-groups', title: 'Groups' do
                 Groups
 
+          - if dashboard_nav_link?(:activity)
             = nav_link(path: 'dashboard#activity') do
               = link_to activity_dashboard_path, title: 'Activity' do
                 Activity
 
+          - if dashboard_nav_link?(:milestones)
             = nav_link(controller: 'dashboard/milestones') do
               = link_to dashboard_milestones_path, class: 'dashboard-shortcuts-milestones', title: 'Milestones' do
                 Milestones
 
+          - if dashboard_nav_link?(:snippets)
             = nav_link(controller: 'dashboard/snippets') do
               = link_to dashboard_snippets_path, class: 'dashboard-shortcuts-snippets', title: 'Snippets' do
                 Snippets
 
   -# Shortcut to Dashboard > Projects
+  - if dashboard_nav_link?(:projects)
     %li.hidden
       = link_to dashboard_projects_path, title: 'Projects', class: 'dashboard-shortcuts-projects' do
         Projects

app/views/layouts/nav/_explore.html.haml

 %ul.list-unstyled.navbar-sub-nav
+  - if explore_nav_link?(:projects)
     = nav_link(path: ['dashboard#show', 'root#show', 'projects#trending', 'projects#starred', 'projects#index'], html_options: {class: 'home'}) do
       = link_to explore_root_path, title: 'Projects', class: 'dashboard-shortcuts-projects' do
         Projects
+  - if explore_nav_link?(:groups)
     = nav_link(controller: [:groups, 'groups/milestones', 'groups/group_members']) do
       = link_to explore_groups_path, title: 'Groups', class: 'dashboard-shortcuts-groups' do
         Groups
+  - if explore_nav_link?(:snippets)
     = nav_link(controller: :snippets) do
       = link_to explore_snippets_path, title: 'Snippets', class: 'dashboard-shortcuts-snippets' do
         Snippets

app/views/layouts/nav/sidebar/_group.html.haml

 - issues_count = IssuesFinder.new(current_user, group_id: @group.id, state: 'opened').execute.count
 - merge_requests_count = MergeRequestsFinder.new(current_user, group_id: @group.id, state: 'opened', non_archived: true).execute.count
 
+- issues_sub_menu_items = ['groups#issues', 'labels#index', 'milestones#index']
+
 .nav-sidebar{ class: ("sidebar-collapsed-desktop" if collapsed_sidebar?) }
   .nav-sidebar-inner-scroll
     .context-header
@@ -10,7 +12,8 @@
         .sidebar-context-title
           = @group.name
     %ul.sidebar-top-level-items
-      = nav_link(path: ['groups#show', 'groups#activity', 'groups#subgroups'], html_options: { class: 'home' }) do
+      - if group_sidebar_link?(:overview)
+        = nav_link(path: ['groups#show', 'groups#activity', 'groups#subgroups', 'analytics#show'], html_options: { class: 'home' }) do
           = link_to group_path(@group) do
             .nav-icon-container
               = sprite_icon('project')
@@ -28,12 +31,14 @@
                 %span
                   Details
 
+            - if group_sidebar_link?(:activity)
               = nav_link(path: 'groups#activity') do
                 = link_to activity_group_path(@group), title: 'Activity' do
                   %span
                     Activity
 
-      = nav_link(path: ['groups#issues', 'labels#index', 'milestones#index']) do
+      - if group_sidebar_link?(:issues)
+        = nav_link(path: issues_sub_menu_items) do
           = link_to issues_group_path(@group) do
             .nav-icon-container
               = sprite_icon('issues')
@@ -53,16 +58,19 @@
                 %span
                   List
 
+            - if group_sidebar_link?(:labels)
               = nav_link(path: 'labels#index') do
                 = link_to group_labels_path(@group), title: 'Labels' do
                   %span
                     Labels
 
+            - if group_sidebar_link?(:milestones)
               = nav_link(path: 'milestones#index') do
                 = link_to group_milestones_path(@group), title: 'Milestones' do
                   %span
                     Milestones
 
+      - if group_sidebar_link?(:merge_requests)
         = nav_link(path: 'groups#merge_requests') do
           = link_to merge_requests_group_path(@group) do
             .nav-icon-container
@@ -76,6 +84,8 @@
                 %strong.fly-out-top-item-name
                   #{ _('Merge Requests') }
                 %span.badge.count.merge_counter.js-merge-counter.fly-out-badge= number_with_delimiter(merge_requests_count)
+
+      - if group_sidebar_link?(:group_members)
         = nav_link(path: 'group_members#index') do
           = link_to group_group_members_path(@group) do
             .nav-icon-container
@@ -87,7 +97,8 @@
               = link_to group_group_members_path(@group) do
                 %strong.fly-out-top-item-name
                   #{ _('Members') }
-      - if current_user && can?(current_user, :admin_group, @group)
+
+      - if group_sidebar_link?(:settings)
         = nav_link(path: group_nav_link_paths) do
           = link_to edit_group_path(@group) do
             .nav-icon-container

app/views/shared/projects/_project.html.haml

@@ -6,7 +6,7 @@
 - user = local_assigns[:user]
 - access = user&.max_member_access_for_project(project.id) unless user.nil?
 - css_class = '' unless local_assigns[:css_class]
-- show_last_commit_as_description = false unless local_assigns[:show_last_commit_as_description] == true && project.commit
+- show_last_commit_as_description = false unless local_assigns[:show_last_commit_as_description] == true && can_show_last_commit_in_list?(project)
 - css_class += " no-description" if project.description.blank? && !show_last_commit_as_description
 - cache_key = project_list_cache_key(project)
 - updated_tooltip = time_ago_with_tooltip(project.last_activity_date)
@@ -47,7 +47,7 @@
       .prepend-top-0
         - if project.archived
           %span.prepend-left-10.label.label-warning archived
-        - if project.pipeline_status.has_status?
+        - if can?(current_user, :read_cross_project) && project.pipeline_status.has_status?
           %span.prepend-left-10
             = render_project_pipeline_status(project.pipeline_status)
         - if forks

app/views/users/show.html.haml

@@ -82,24 +82,30 @@
       .fade-left= icon('angle-left')
       .fade-right= icon('angle-right')
       %ul.nav-links.user-profile-nav.scrolling-tabs
+        - if profile_tab?(:activity)
           %li.js-activity-tab
             = link_to user_path, data: { target: 'div#activity', action: 'activity', toggle: 'tab' } do
               Activity
+        - if profile_tab?(:groups)
           %li.js-groups-tab
             = link_to user_groups_path, data: { target: 'div#groups', action: 'groups', toggle: 'tab', endpoint: user_groups_path(format: :json) } do
               Groups
+        - if profile_tab?(:contributed)
           %li.js-contributed-tab
             = link_to user_contributed_projects_path, data: { target: 'div#contributed', action: 'contributed', toggle: 'tab', endpoint: user_contributed_projects_path(format: :json) } do
               Contributed projects
+        - if profile_tab?(:projects)
           %li.js-projects-tab
             = link_to user_projects_path, data: { target: 'div#projects', action: 'projects', toggle: 'tab', endpoint: user_projects_path(format: :json) } do
               Personal projects
+        - if profile_tab?(:snippets)
           %li.js-snippets-tab
             = link_to user_snippets_path, data: { target: 'div#snippets', action: 'snippets', toggle: 'tab', endpoint: user_snippets_path(format: :json) } do
               Snippets
 
   %div{ class: container_class }
     .tab-content
+      - if profile_tab?(:activity)
         #activity.tab-pane
           .row-content-block.calender-block.white.second-block.hidden-xs
             .user-calendar{ data: { calendar_path: user_calendar_path(@user, :json), calendar_activities_path: user_calendar_activities_path, utc_offset: Time.zone.utc_offset } }
@@ -107,20 +113,25 @@
                 %i.fa.fa-spinner.fa-spin
             .user-calendar-activities
 
+          - if can?(current_user, :read_cross_project)
             %h4.prepend-top-20
               Most Recent Activity
             .content_list{ data: { href: user_path } }
             = spinner
 
+      - if profile_tab?(:groups)
         #groups.tab-pane
           -# This tab is always loaded via AJAX
 
+      - if profile_tab?(:contributed)
         #contributed.tab-pane
           -# This tab is always loaded via AJAX
 
+      - if profile_tab?(:projects)
         #projects.tab-pane
           -# This tab is always loaded via AJAX
 
+      - if profile_tab?(:snippets)
         #snippets.tab-pane
           -# This tab is always loaded via AJAX
 

changelogs/unreleased-ee/bvl-external-policy-classification.yml

+---
+title: Authorize project access with an external service
+merge_request: 4675
+author:
+type: added

config/initializers/0_as_concern.rb

+# This module is based on: https://gist.github.com/bcardarella/5735987
+
+module Prependable
+  def prepend_features(base)
+    if base.instance_variable_defined?(:@_dependencies)
+      base.instance_variable_get(:@_dependencies) << self
+      false
+    else
+      return false if base < self
+
+      super
+      base.singleton_class.send(:prepend, const_get('ClassMethods')) if const_defined?(:ClassMethods)
+      @_dependencies.each { |dep| base.send(:prepend, dep) } # rubocop:disable Gitlab/ModuleWithInstanceVariables
+      base.class_eval(&@_included_block) if instance_variable_defined?(:@_included_block) # rubocop:disable Gitlab/ModuleWithInstanceVariables
+    end
+  end
+end
+
+module ActiveSupport
+  module Concern
+    prepend Prependable
+
+    alias_method :prepended, :included
+  end
+end

lib/api/helpers.rb

@@ -172,7 +172,7 @@ module API
 
     def find_project_snippet(id)
       finder_params = { project: user_project }
-      SnippetsFinder.new(current_user, finder_params).execute.find(id)
+      SnippetsFinder.new(current_user, finder_params).find(id)
     end
 
     def find_merge_request_with_access(iid, access_level = :read_merge_request)

lib/api/settings.rb

@@ -147,7 +147,7 @@ module API
         attrs[:password_authentication_enabled_for_web] = attrs.delete(:password_authentication_enabled)
       end
 
-      if current_settings.update_attributes(attrs)
+      if ApplicationSettings::UpdateService.new(current_settings, current_user, attrs).execute
         present current_settings, with: Entities::ApplicationSetting
       else
         render_validation_error!(current_settings)

lib/banzai/filter/cross_project_issuable_information_filter.rb

+module Banzai
+  module Filter
+    # HTML filter that removes sensitive information from cross project
+    # issue references.
+    #
+    # The link to the issue or merge request is preserved only the IID is shown,
+    # but all other info is removed.
+    class CrossProjectIssuableInformationFilter < HTML::Pipeline::Filter
+      def call
+        return doc if can_read_cross_project?
+
+        extractor = Banzai::IssuableExtractor.new(project, current_user)
+        issuables = extractor.extract([doc])
+
+        issuables.each do |node, issuable|
+          next if issuable.project == project
+
+          node['class'] = node['class'].gsub('has-tooltip', '')
+          node['title'] = nil
+        end
+
+        doc
+      end
+
+      private
+
+      def project
+        context[:project]
+      end
+
+      def can_read_cross_project?
+        Ability.allowed?(current_user, :read_cross_project)
+      end
+
+      def current_user
+        context[:current_user]
+      end
+    end
+  end
+end

lib/banzai/filter/issuable_state_filter.rb

@@ -15,6 +15,8 @@ module Banzai
         issuables = extractor.extract([doc])
 
         issuables.each do |node, issuable|
+          next if !can_read_cross_project? && issuable.project != project
+
           if VISIBLE_STATES.include?(issuable.state) && node.inner_html == issuable.reference_link_text(project)
             node.content += " (#{issuable.state})"
           end
@@ -25,6 +27,10 @@ module Banzai
 
       private
 
+      def can_read_cross_project?
+        Ability.allowed?(current_user, :read_cross_project)
+      end
+
       def current_user
         context[:current_user]
       end

lib/banzai/filter/milestone_reference_filter.rb

@@ -64,7 +64,7 @@ module Banzai
           finder_params[:group_ids] = [project.group.id]
         end
 
-        MilestonesFinder.new(finder_params).execute.find_by(params)
+        MilestonesFinder.new(finder_params).find_by(params)
       end
 
       def url_for_object(milestone, project)

lib/banzai/pipeline/post_process_pipeline.rb

@@ -6,6 +6,7 @@ module Banzai
           Filter::RedactorFilter,
           Filter::RelativeLinkFilter,
           Filter::IssuableStateFilter,
+          Filter::CrossProjectIssuableInformationFilter,
           Filter::AbsoluteLinkFilter
         ]
       end

lib/banzai/reference_parser/issuable_parser.rb

@@ -18,7 +18,7 @@ module Banzai
       end
 
       def can_read_reference?(user, issuable)
-        can?(user, "read_#{issuable.class.to_s.underscore}".to_sym, issuable)
+        can?(user, "read_#{issuable.class.to_s.underscore}_iid".to_sym, issuable)
       end
     end
   end

lib/banzai/reference_parser/issue_parser.rb

@@ -5,12 +5,31 @@ module Banzai
 
       def nodes_visible_to_user(user, nodes)
         issues = records_for_nodes(nodes)
+        issues_to_check = issues.values
 
-        readable_issues = Ability
-          .issues_readable_by_user(issues.values, user).to_set
+        unless can?(user, :read_cross_project)
+          issues_to_check, cross_project_issues = issues_to_check.partition do |issue|
+            issue.project == project
+          end
+        end
+
+        readable_issues = Ability.issues_readable_by_user(issues_to_check, user).to_set
 
         nodes.select do |node|
-          readable_issues.include?(issues[node])
+          issue_in_node = issues[node]
+
+          # We check the inclusion of readable issues first because it's faster.
+          #
+          # But we need to fall back to `read_issue_iid` if the user cannot read
+          # cross project, since it might be possible the user can see the IID
+          # but not the issue.
+          if readable_issues.include?(issue_in_node)
+            true
+          elsif cross_project_issues&.include?(issue_in_node)
+            can_read_reference?(user, issue_in_node)
+          else
+            false
+          end
         end
       end
 

lib/gitlab/contributions_calendar.rb

@@ -34,6 +34,8 @@ module Gitlab
     end
 
     def events_by_date(date)
+      return Event.none unless can_read_cross_project?
+
       events = Event.contributions.where(author_id: contributor.id)
         .where(created_at: date.beginning_of_day..date.end_of_day)
         .where(project_id: projects)
@@ -53,6 +55,10 @@ module Gitlab
 
     private
 
+    def can_read_cross_project?
+      Ability.allowed?(current_user, :read_cross_project)
+    end
+
     def event_counts(date_from, feature)
       t = Event.arel_table
 

lib/gitlab/cross_project_access.rb

+module Gitlab
+  class CrossProjectAccess
+    class << self
+      delegate :add_check, :find_check, :checks,
+               to: :instance
+    end
+
+    def self.instance
+      @instance ||= new
+    end
+
+    attr_reader :checks
+
+    def initialize
+      @checks = {}
+    end
+
+    def add_check(
+          klass,
+          actions: {},
+          positive_condition: nil,
+          negative_condition: nil,
+          skip: false)
+
+      new_check = CheckInfo.new(actions,
+                                positive_condition,
+                                negative_condition,
+                                skip
+                               )
+
+      @checks[klass] ||= Gitlab::CrossProjectAccess::CheckCollection.new
+      @checks[klass].add_check(new_check)
+      recalculate_checks_for_class(klass)
+
+      @checks[klass]
+    end
+
+    def find_check(object)
+      @cached_checks ||= Hash.new do |cache, new_class|
+        parent_classes = @checks.keys.select { |existing_class| new_class <= existing_class }
+        closest_class = closest_parent(parent_classes, new_class)
+        cache[new_class] = @checks[closest_class]
+      end
+
+      @cached_checks[object.class]
+    end
+
+    private
+
+    def recalculate_checks_for_class(klass)
+      new_collection = @checks[klass]
+
+      @checks.each do |existing_class, existing_check_collection|
+        if existing_class < klass
+          existing_check_collection.add_collection(new_collection)
+        elsif klass < existing_class
+          new_collection.add_collection(existing_check_collection)
+        end
+      end
+    end
+
+    def closest_parent(classes, subject)
+      relevant_ancestors = subject.ancestors & classes
+      relevant_ancestors.first
+    end
+  end
+end

lib/gitlab/cross_project_access/check_collection.rb

+module Gitlab
+  class CrossProjectAccess
+    class CheckCollection
+      attr_reader :checks
+
+      def initialize
+        @checks = []
+      end
+
+      def add_collection(collection)
+        @checks |= collection.checks
+      end
+
+      def add_check(check)
+        @checks << check
+      end
+
+      def should_run?(object)
+        skips, runs = arranged_checks
+
+        # If one rule tells us to skip, we skip the cross project check
+        return false if skips.any? { |check| check.should_skip?(object) }
+
+        # If the rule isn't skipped, we run it if any of the checks says we
+        # should run
+        runs.any? { |check| check.should_run?(object) }
+      end
+
+      def arranged_checks
+        return [@skips, @runs] if @skips && @runs
+
+        @skips = []
+        @runs = []
+
+        @checks.each do |check|
+          if check.skip
+            @skips << check
+          else
+            @runs << check
+          end
+        end
+
+        [@skips, @runs]
+      end
+    end
+  end
+end

lib/gitlab/cross_project_access/check_info.rb

+module Gitlab
+  class CrossProjectAccess
+    class CheckInfo
+      attr_accessor :actions, :positive_condition, :negative_condition, :skip
+
+      def initialize(actions, positive_condition, negative_condition, skip)
+        @actions = actions
+        @positive_condition = positive_condition
+        @negative_condition = negative_condition
+        @skip = skip
+      end
+
+      def should_skip?(object)
+        return !should_run?(object) unless @skip
+
+        skip_for_action = @actions[current_action(object)]
+        skip_for_action = false if @actions[current_action(object)].nil?
+
+        # We need to do the opposite of what was defined in the following cases:
+        # - skip_cross_project_access_check index: true, if: -> { false }
+        # - skip_cross_project_access_check index: true, unless: -> { true }
+        if positive_condition_is_false?(object)
+          skip_for_action = !skip_for_action
+        end
+
+        if negative_condition_is_true?(object)
+          skip_for_action = !skip_for_action
+        end
+
+        skip_for_action
+      end
+
+      def should_run?(object)
+        return !should_skip?(object) if @skip
+
+        run_for_action = @actions[current_action(object)]
+        run_for_action = true if @actions[current_action(object)].nil?
+
+        # We need to do the opposite of what was defined in the following cases:
+        # - requires_cross_project_access index: true, if: -> { false }
+        # - requires_cross_project_access index: true, unless: -> { true }
+        if positive_condition_is_false?(object)
+          run_for_action = !run_for_action
+        end
+
+        if negative_condition_is_true?(object)
+          run_for_action = !run_for_action
+        end
+
+        run_for_action
+      end
+
+      def positive_condition_is_false?(object)
+        @positive_condition && !object.instance_exec(&@positive_condition)
+      end
+
+      def negative_condition_is_true?(object)
+        @negative_condition && object.instance_exec(&@negative_condition)
+      end
+
+      def current_action(object)
+        object.respond_to?(:action_name) ? object.action_name.to_sym : nil
+      end
+    end
+  end
+end

lib/gitlab/cross_project_access/class_methods.rb

+module Gitlab
+  class CrossProjectAccess
+    module ClassMethods
+      def requires_cross_project_access(*args)
+        positive_condition, negative_condition, actions = extract_params(args)
+
+        Gitlab::CrossProjectAccess.add_check(
+          self,
+          actions: actions,
+          positive_condition: positive_condition,
+          negative_condition: negative_condition
+        )
+      end
+
+      def skip_cross_project_access_check(*args)
+        positive_condition, negative_condition, actions = extract_params(args)
+
+        Gitlab::CrossProjectAccess.add_check(
+          self,
+          actions: actions,
+          positive_condition: positive_condition,
+          negative_condition: negative_condition,
+          skip: true
+        )
+      end
+
+      private
+
+      def extract_params(args)
+        actions = {}
+        positive_condition = nil
+        negative_condition = nil
+
+        args.each do |argument|
+          if argument.is_a?(Hash)
+            positive_condition = argument.delete(:if)
+            negative_condition = argument.delete(:unless)
+            actions.merge!(argument)
+          else
+            actions[argument] = true
+          end
+        end
+
+        [positive_condition, negative_condition, actions]
+      end
+    end
+  end
+end

lib/gitlab/user_access.rb

@@ -65,7 +65,7 @@ module Gitlab
       return false unless can_access_git?
 
       if protected?(ProtectedBranch, project, ref)
-        return true if project.empty_repo? && project.user_can_push_to_empty_repo?(user)
+        return true if project.user_can_push_to_empty_repo?(user)
 
         protected_branch_accessible_to?(ref, action: :push)
       else

locale/gitlab.pot

@@ -8,8 +8,8 @@ msgid ""
 msgstr ""
 "Project-Id-Version: gitlab 1.0.0\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2018-02-07 11:38-0600\n"
-"PO-Revision-Date: 2018-02-07 11:38-0600\n"
+"POT-Creation-Date: 2018-02-20 10:26+0100\n"
+"PO-Revision-Date: 2018-02-20 10:26+0100\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
 "Language: \n"
@@ -150,6 +150,39 @@ msgstr ""
 msgid "AdminHealthPageLink|health page"
 msgstr ""
 
+msgid "AdminProjects|Delete"
+msgstr ""
+
+msgid "AdminProjects|Delete Project %{projectName}?"
+msgstr ""
+
+msgid "AdminProjects|Delete project"
+msgstr ""
+
+msgid "AdminSettings|Specify a domain to use by default for every project's Auto Review Apps and Auto Deploy stages."
+msgstr ""
+
+msgid "AdminUsers|Block user"
+msgstr ""
+
+msgid "AdminUsers|Delete User %{username} and contributions?"
+msgstr ""
+
+msgid "AdminUsers|Delete User %{username}?"
+msgstr ""
+
+msgid "AdminUsers|Delete user"
+msgstr ""
+
+msgid "AdminUsers|Delete user and contributions"
+msgstr ""
+
+msgid "AdminUsers|To confirm, type %{projectName}"
+msgstr ""
+
+msgid "AdminUsers|To confirm, type %{username}"
+msgstr ""
+
 msgid "Advanced settings"
 msgstr ""
 
@@ -177,9 +210,21 @@ msgstr ""
 msgid "An error occurred while getting projects"
 msgstr ""
 
+msgid "An error occurred while importing project"
+msgstr ""
+
+msgid "An error occurred while loading commits"
+msgstr ""
+
+msgid "An error occurred while loading diff"
+msgstr ""
+
 msgid "An error occurred while loading filenames"
 msgstr ""
 
+msgid "An error occurred while loading the file"
+msgstr ""
+
 msgid "An error occurred while rendering KaTeX"
 msgstr ""
 
@@ -192,6 +237,9 @@ msgstr ""
 msgid "An error occurred while retrieving diff"
 msgstr ""
 
+msgid "An error occurred while saving assignees"
+msgstr ""
+
 msgid "An error occurred while validating username"
 msgstr ""
 
@@ -1018,6 +1066,9 @@ msgstr ""
 msgid "Create a personal access token on your account to pull or push via %{protocol}."
 msgstr ""
 
+msgid "Create branch"
+msgstr ""
+
 msgid "Create directory"
 msgstr ""
 
@@ -1033,6 +1084,9 @@ msgstr ""
 msgid "Create merge request"
 msgstr ""
 
+msgid "Create merge request and branch"
+msgstr ""
+
 msgid "Create new branch"
 msgstr ""
 
@@ -1290,9 +1344,15 @@ msgstr ""
 msgid "Failed to change the owner"
 msgstr ""
 
+msgid "Failed to remove issue from board, please try again."
+msgstr ""
+
 msgid "Failed to remove the pipeline schedule"
 msgstr ""
 
+msgid "Failed to update issues, please try again."
+msgstr ""
+
 msgid "Feb"
 msgstr ""
 
@@ -1985,6 +2045,24 @@ msgstr ""
 msgid "Pipelines|Get started with Pipelines"
 msgstr ""
 
+msgid "Pipeline|Retry pipeline"
+msgstr ""
+
+msgid "Pipeline|Retry pipeline #%{id}?"
+msgstr ""
+
+msgid "Pipeline|Stop pipeline"
+msgstr ""
+
+msgid "Pipeline|Stop pipeline #%{id}?"
+msgstr ""
+
+msgid "Pipeline|You’re about to retry pipeline %{id}."
+msgstr ""
+
+msgid "Pipeline|You’re about to stop pipeline %{id}."
+msgstr ""
+
 msgid "Pipeline|all"
 msgstr ""
 
@@ -2144,12 +2222,30 @@ msgstr ""
 msgid "ProjectsDropdown|This feature requires browser localStorage support"
 msgstr ""
 
+msgid "PrometheusService|Active"
+msgstr ""
+
+msgid "PrometheusService|Auto configuration"
+msgstr ""
+
+msgid "PrometheusService|Automatically deploy and configure Prometheus on your clusters to monitor your project’s environments"
+msgstr ""
+
 msgid "PrometheusService|By default, Prometheus listens on ‘http://localhost:9090’. It’s not recommended to change the default address and port as this might affect or conflict with other services running on the GitLab server."
 msgstr ""
 
 msgid "PrometheusService|Finding and configuring metrics..."
 msgstr ""
 
+msgid "PrometheusService|Install Prometheus on clusters"
+msgstr ""
+
+msgid "PrometheusService|Manage clusters"
+msgstr ""
+
+msgid "PrometheusService|Manual configuration"
+msgstr ""
+
 msgid "PrometheusService|Metrics"
 msgstr ""
 
@@ -2171,9 +2267,18 @@ msgstr ""
 msgid "PrometheusService|Prometheus API Base URL, like http://prometheus.example.com/"
 msgstr ""
 
+msgid "PrometheusService|Prometheus is being automatically managed on your clusters"
+msgstr ""
+
 msgid "PrometheusService|Time-series monitoring service"
 msgstr ""
 
+msgid "PrometheusService|To enable manual configuration, uninstall Prometheus from your clusters"
+msgstr ""
+
+msgid "PrometheusService|To enable the installation of Prometheus on your clusters, deactivate the manual configuration below"
+msgstr ""
+
 msgid "PrometheusService|View environments"
 msgstr ""
 
@@ -2376,12 +2481,18 @@ msgstr ""
 msgid "Something went wrong when toggling the button"
 msgstr ""
 
+msgid "Something went wrong while closing the issue. Please try again later"
+msgstr ""
+
 msgid "Something went wrong while fetching the projects."
 msgstr ""
 
 msgid "Something went wrong while fetching the registry list."
 msgstr ""
 
+msgid "Something went wrong while reopening the issue. Please try again later"
+msgstr ""
+
 msgid "Something went wrong. Please try again."
 msgstr ""
 
@@ -2478,6 +2589,9 @@ msgstr ""
 msgid "Source"
 msgstr ""
 
+msgid "Source (branch or tag)"
+msgstr ""
+
 msgid "Source code"
 msgstr ""
 
@@ -2738,6 +2852,9 @@ msgstr ""
 msgid "This merge request is locked."
 msgstr ""
 
+msgid "This page is unavailable because you are not allowed to read information across multiple projects."
+msgstr ""
+
 msgid "This project"
 msgstr ""
 
@@ -2934,9 +3051,6 @@ msgstr ""
 msgid "Trigger this manual action"
 msgstr ""
 
-msgid "Type %{value} to confirm:"
-msgstr ""
-
 msgid "Unable to reset project cache."
 msgstr ""
 
@@ -3229,6 +3343,9 @@ msgid_plural "merge requests"
 msgstr[0] ""
 msgstr[1] ""
 
+msgid "mrWidget| Please restore it or use a different %{missingBranchName} branch"
+msgstr ""
+
 msgid "mrWidget|Cancel automatic merge"
 msgstr ""
 
@@ -3262,6 +3379,9 @@ msgstr ""
 msgid "mrWidget|If the %{branch} branch exists in your local repository, you can merge this merge request manually using the"
 msgstr ""
 
+msgid "mrWidget|If the %{missingBranchName} branch exists in your local repository, you can merge this merge request manually using the command line"
+msgstr ""
+
 msgid "mrWidget|Mentions"
 msgstr ""
 
@@ -3349,6 +3469,9 @@ msgstr ""
 msgid "mrWidget|You can remove source branch now"
 msgstr ""
 
+msgid "mrWidget|branch does not exist."
+msgstr ""
+
 msgid "mrWidget|command line"
 msgstr ""
 

spec/controllers/boards/issues_controller_spec.rb

@@ -86,6 +86,7 @@ describe Boards::IssuesController do
 
     context 'with unauthorized user' do
       before do
+        allow(Ability).to receive(:allowed?).and_call_original
         allow(Ability).to receive(:allowed?).with(user, :read_project, project).and_return(true)
         allow(Ability).to receive(:allowed?).with(user, :read_issue, project).and_return(false)
       end

spec/controllers/concerns/controller_with_cross_project_access_check_spec.rb

+require 'spec_helper'
+
+describe ControllerWithCrossProjectAccessCheck do
+  let(:user) { create(:user) }
+
+  before do
+    sign_in user
+  end
+
+  render_views
+
+  context 'When reading cross project is not allowed' do
+    before do
+      allow(Ability).to receive(:allowed).and_call_original
+      allow(Ability).to receive(:allowed?)
+                          .with(user, :read_cross_project, :global)
+                          .and_return(false)
+    end
+
+    describe '#requires_cross_project_access' do
+      controller(ApplicationController) do
+        # `described_class` is not available in this context
+        include ControllerWithCrossProjectAccessCheck # rubocop:disable RSpec/DescribedClass
+
+        requires_cross_project_access :index, show: false,
+                                              unless: -> { unless_condition },
+                                              if: -> { if_condition }
+
+        def index
+          render nothing: true
+        end
+
+        def show
+          render nothing: true
+        end
+
+        def unless_condition
+          false
+        end
+
+        def if_condition
+          true
+        end
+      end
+
+      it 'renders a 404 with trying to access a cross project page' do
+        message = "This page is unavailable because you are not allowed to read "\
+                  "information across multiple projects."
+
+        get :index
+
+        expect(response).to have_gitlab_http_status(404)
+        expect(response.body).to match(/#{message}/)
+      end
+
+      it 'is skipped when the `if` condition returns false' do
+        expect(controller).to receive(:if_condition).and_return(false)
+
+        get :index
+
+        expect(response).to have_gitlab_http_status(200)
+      end
+
+      it 'is skipped when the `unless` condition returns true' do
+        expect(controller).to receive(:unless_condition).and_return(true)
+
+        get :index
+
+        expect(response).to have_gitlab_http_status(200)
+      end
+
+      it 'correctly renders an action that does not require cross project access' do
+        get :show, id: 'nothing'
+
+        expect(response).to have_gitlab_http_status(200)
+      end
+    end
+
+    describe '#skip_cross_project_access_check' do
+      controller(ApplicationController) do
+        # `described_class` is not available in this context
+        include ControllerWithCrossProjectAccessCheck # rubocop:disable RSpec/DescribedClass
+
+        requires_cross_project_access
+
+        skip_cross_project_access_check index: true, show: false,
+                                        unless: -> { unless_condition },
+                                        if: -> { if_condition }
+
+        def index
+          render nothing: true
+        end
+
+        def show
+          render nothing: true
+        end
+
+        def edit
+          render nothing: true
+        end
+
+        def unless_condition
+          false
+        end
+
+        def if_condition
+          true
+        end
+      end
+
+      it 'renders a success when the check is skipped' do
+        get :index
+
+        expect(response).to have_gitlab_http_status(200)
+      end
+
+      it 'is executed when the `if` condition returns false' do
+        expect(controller).to receive(:if_condition).and_return(false)
+
+        get :index
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+
+      it 'is executed when the `unless` condition returns true' do
+        expect(controller).to receive(:unless_condition).and_return(true)
+
+        get :index
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+
+      it 'does not skip the check on an action that is not skipped' do
+        get :show, id: 'hello'
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+
+      it 'does not skip the check on an action that was not defined to skip' do
+        get :edit, id: 'hello'
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+    end
+  end
+end

spec/controllers/projects/merge_requests/creations_controller_spec.rb

@@ -17,7 +17,7 @@ describe Projects::MergeRequests::CreationsController do
 
   before do
     fork_project.add_master(user)
-
+    Projects::ForkService.new(project, user).execute(fork_project)
     sign_in(user)
   end
 
@@ -125,4 +125,66 @@ describe Projects::MergeRequests::CreationsController do
       end
     end
   end
+
+  describe 'GET #branch_to' do
+    before do
+      allow(Ability).to receive(:allowed?).and_call_original
+    end
+
+    it 'fetches the commit if a user has access' do
+      expect(Ability).to receive(:allowed?).with(user, :read_project, project) { true }
+
+      get :branch_to,
+          namespace_id: fork_project.namespace,
+          project_id: fork_project,
+          target_project_id: project.id,
+          ref: 'master'
+
+      expect(assigns(:commit)).not_to be_nil
+      expect(response).to have_gitlab_http_status(200)
+    end
+
+    it 'does not load the commit when the user cannot read the project' do
+      expect(Ability).to receive(:allowed?).with(user, :read_project, project) { false }
+
+      get :branch_to,
+          namespace_id: fork_project.namespace,
+          project_id: fork_project,
+          target_project_id: project.id,
+          ref: 'master'
+
+      expect(assigns(:commit)).to be_nil
+      expect(response).to have_gitlab_http_status(200)
+    end
+  end
+
+  describe 'GET #update_branches' do
+    before do
+      allow(Ability).to receive(:allowed?).and_call_original
+    end
+
+    it 'lists the branches of another fork if the user has access' do
+      expect(Ability).to receive(:allowed?).with(user, :read_project, project) { true }
+
+      get :update_branches,
+          namespace_id: fork_project.namespace,
+          project_id: fork_project,
+          target_project_id: project.id
+
+      expect(assigns(:target_branches)).not_to be_empty
+      expect(response).to have_gitlab_http_status(200)
+    end
+
+    it 'does not list branches when the user cannot read the project' do
+      expect(Ability).to receive(:allowed?).with(user, :read_project, project) { false }
+
+      get :update_branches,
+          namespace_id: fork_project.namespace,
+          project_id: fork_project,
+          target_project_id: project.id
+
+      expect(response).to have_gitlab_http_status(200)
+      expect(assigns(:target_branches)).to eq([])
+    end
+  end
 end

spec/controllers/search_controller_spec.rb

@@ -16,6 +16,32 @@ describe SearchController do
     expect(assigns[:search_objects].first).to eq note
   end
 
+  context 'when the user cannot read cross project' do
+    before do
+      allow(Ability).to receive(:allowed?).and_call_original
+      allow(Ability).to receive(:allowed?)
+                          .with(user, :read_cross_project, :global) { false }
+    end
+
+    it 'still allows accessing the search page' do
+      get :show
+
+      expect(response).to have_gitlab_http_status(200)
+    end
+
+    it 'still blocks searches without a project_id' do
+      get :show, search: 'hello'
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it 'allows searches with a project_id' do
+      get :show, search: 'hello', project_id: create(:project, :public).id
+
+      expect(response).to have_gitlab_http_status(200)
+    end
+  end
+
   context 'on restricted projects' do
     context 'when signed out' do
       before do

spec/controllers/users_controller_spec.rb

@@ -74,6 +74,31 @@ describe UsersController do
         end
       end
     end
+
+    context 'json with events' do
+      let(:project) { create(:project) }
+      before do
+        project.add_developer(user)
+        Gitlab::DataBuilder::Push.build_sample(project, user)
+
+        sign_in(user)
+      end
+
+      it 'loads events' do
+        get :show, username: user, format: :json
+
+        expect(assigns(:events)).not_to be_empty
+      end
+
+      it 'hides events if the user cannot read cross project' do
+        allow(Ability).to receive(:allowed?).and_call_original
+        expect(Ability).to receive(:allowed?).with(user, :read_cross_project) { false }
+
+        get :show, username: user, format: :json
+
+        expect(assigns(:events)).to be_empty
+      end
+    end
   end
 
   describe 'GET #calendar' do

spec/features/users/show_spec.rb

+require 'spec_helper'
+
+describe 'User page' do
+  let(:user) { create(:user) }
+
+  it 'shows all the tabs' do
+    visit(user_path(user))
+
+    page.within '.nav-links' do
+      expect(page).to have_link('Activity')
+      expect(page).to have_link('Groups')
+      expect(page).to have_link('Contributed projects')
+      expect(page).to have_link('Personal projects')
+      expect(page).to have_link('Snippets')
+    end
+  end
+end

spec/finders/concerns/finder_methods_spec.rb

+require 'spec_helper'
+
+describe FinderMethods do
+  let(:finder_class) do
+    Class.new do
+      include FinderMethods
+
+      attr_reader :current_user
+
+      def initialize(user)
+        @current_user = user
+      end
+
+      def execute
+        Project.all
+      end
+    end
+  end
+
+  let(:user) { create(:user) }
+  let(:finder) { finder_class.new(user) }
+  let(:authorized_project) { create(:project) }
+  let(:unauthorized_project) { create(:project) }
+
+  before do
+    authorized_project.add_developer(user)
+  end
+
+  describe '#find_by!' do
+    it 'returns the project if the user has access' do
+      expect(finder.find_by!(id: authorized_project.id)).to eq(authorized_project)
+    end
+
+    it 'raises not found when the project is not found' do
+      expect { finder.find_by!(id: 0) }.to raise_error(ActiveRecord::RecordNotFound)
+    end
+
+    it 'raises not found the user does not have access' do
+      expect { finder.find_by!(id: unauthorized_project.id) }.to raise_error(ActiveRecord::RecordNotFound)
+    end
+  end
+
+  describe '#find' do
+    it 'returns the project if the user has access' do
+      expect(finder.find(authorized_project.id)).to eq(authorized_project)
+    end
+
+    it 'raises not found when the project is not found' do
+      expect { finder.find(0) }.to raise_error(ActiveRecord::RecordNotFound)
+    end
+
+    it 'raises not found the user does not have access' do
+      expect { finder.find(unauthorized_project.id) }.to raise_error(ActiveRecord::RecordNotFound)
+    end
+  end
+
+  describe '#find_by' do
+    it 'returns the project if the user has access' do
+      expect(finder.find_by(id: authorized_project.id)).to eq(authorized_project)
+    end
+
+    it 'returns nil when the project is not found' do
+      expect(finder.find_by(id: 0)).to be_nil
+    end
+
+    it 'returns nil when the user does not have access' do
+      expect(finder.find_by(id: unauthorized_project.id)).to be_nil
+    end
+  end
+end

spec/finders/concerns/finder_with_cross_project_access_spec.rb

+require 'spec_helper'
+
+describe FinderWithCrossProjectAccess do
+  let(:finder_class) do
+    Class.new do
+      prepend FinderWithCrossProjectAccess
+      include FinderMethods
+
+      requires_cross_project_access if: -> { requires_access? }
+
+      attr_reader :current_user
+
+      def initialize(user)
+        @current_user = user
+      end
+
+      def execute
+        Issue.all
+      end
+    end
+  end
+
+  let(:user) { create(:user) }
+  subject(:finder) { finder_class.new(user) }
+  let!(:result) { create(:issue) }
+
+  before do
+    result.project.add_master(user)
+  end
+
+  def expect_access_check_on_result
+    expect(finder).not_to receive(:requires_access?)
+    expect(Ability).to receive(:allowed?).with(user, :read_issue, result).and_call_original
+  end
+
+  context 'when the user cannot read cross project' do
+    before do
+      allow(Ability).to receive(:allowed?).and_call_original
+      allow(Ability).to receive(:allowed?).with(user, :read_cross_project)
+                          .and_return(false)
+    end
+
+    describe '#execute' do
+      it 'returns a issue if the check is disabled' do
+        expect(finder).to receive(:requires_access?).and_return(false)
+
+        expect(finder.execute).to include(result)
+      end
+
+      it 'returns an empty relation when the check is enabled' do
+        expect(finder).to receive(:requires_access?).and_return(true)
+
+        expect(finder.execute).to be_empty
+      end
+
+      it 'only queries once when check is enabled' do
+        expect(finder).to receive(:requires_access?).and_return(true)
+
+        expect { finder.execute }.not_to exceed_query_limit(1)
+      end
+
+      it 'only queries once when check is disabled' do
+        expect(finder).to receive(:requires_access?).and_return(false)
+
+        expect { finder.execute }.not_to exceed_query_limit(1)
+      end
+    end
+
+    describe '#find' do
+      it 'checks the accessibility of the subject directly' do
+        expect_access_check_on_result
+
+        finder.find(result.id)
+      end
+
+      it 'returns the issue' do
+        expect(finder.find(result.id)).to eq(result)
+      end
+    end
+
+    describe '#find_by' do
+      it 'checks the accessibility of the subject directly' do
+        expect_access_check_on_result
+
+        finder.find_by(id: result.id)
+      end
+    end
+
+    describe '#find_by!' do
+      it 'checks the accessibility of the subject directly' do
+        expect_access_check_on_result
+
+        finder.find_by!(id: result.id)
+      end
+
+      it 're-enables the check after the find failed' do
+        finder.find_by!(id: 9999) rescue ActiveRecord::RecordNotFound
+
+        expect(finder.instance_variable_get(:@should_skip_cross_project_check))
+          .to eq(false)
+      end
+    end
+  end
+
+  context 'when the user can read cross project' do
+    before do
+      allow(Ability).to receive(:allowed?).and_call_original
+      allow(Ability).to receive(:allowed?).with(user, :read_cross_project)
+                          .and_return(true)
+    end
+
+    it 'returns the result' do
+      expect(finder).not_to receive(:requires_access?)
+
+      expect(finder.execute).to include(result)
+    end
+  end
+end

spec/finders/events_finder_spec.rb

@@ -26,6 +26,14 @@ describe EventsFinder do
 
       expect(events).not_to include(opened_merge_request_event)
     end
+
+    it 'returns nothing when the current user cannot read cross project' do
+      expect(Ability).to receive(:allowed?).with(user, :read_cross_project) { false }
+
+      events = described_class.new(source: user, current_user: user).execute
+
+      expect(events).to be_empty
+    end
   end
 
   context 'when targeting a project' do

spec/finders/milestones_finder_spec.rb

@@ -70,4 +70,12 @@ describe MilestonesFinder do
       expect(result.to_a).to contain_exactly(milestone_1)
     end
   end
+
+  describe '#find_by' do
+    it 'finds a single milestone' do
+      finder = described_class.new(project_ids: [project_1.id], state: 'all')
+
+      expect(finder.find_by(iid: milestone_3.iid)).to eq(milestone_3)
+    end
+  end
 end

spec/finders/snippets_finder_spec.rb

@@ -162,8 +162,26 @@ describe SnippetsFinder do
     end
   end
 
-  describe "#execute" do
-    # Snippet visibility scenarios are included in more details in spec/support/snippet_visibility.rb
-    include_examples 'snippet visibility', described_class
+  describe '#execute' do
+    let(:project) { create(:project, :public) }
+    let!(:project_snippet) { create(:project_snippet, :public, project: project) }
+    let!(:personal_snippet) { create(:personal_snippet, :public) }
+    let(:user) { create(:user) }
+    subject(:finder) { described_class.new(user) }
+
+    it 'returns project- and personal snippets' do
+      expect(finder.execute).to contain_exactly(project_snippet, personal_snippet)
+    end
+
+    context 'when the user cannot read cross project' do
+      before do
+        allow(Ability).to receive(:allowed?).and_call_original
+        allow(Ability).to receive(:allowed?).with(user, :read_cross_project) { false }
+      end
+
+      it 'returns only personal snippets when the user cannot read cross project' do
+        expect(finder.execute).to contain_exactly(personal_snippet)
+      end
+    end
   end
 end

spec/finders/user_recent_events_finder_spec.rb

+require 'spec_helper'
+
+describe UserRecentEventsFinder do
+  let(:user) { create(:user) }
+  let(:project) { create(:project) }
+  let(:project_owner) { project.creator }
+  let!(:event) { create(:event, project: project, author: project_owner) }
+
+  subject(:finder) { described_class.new(user, project_owner) }
+
+  describe '#execute' do
+    it 'does not include the event when a user does not have access to the project' do
+      expect(finder.execute).to be_empty
+    end
+
+    context 'when the user has access to a project' do
+      before do
+        project.add_developer(user)
+      end
+
+      it 'includes the event' do
+        expect(finder.execute).to include(event)
+      end
+
+      it 'does not include the event if the user cannot read cross project' do
+        expect(Ability).to receive(:allowed?).with(user, :read_cross_project) { false }
+        expect(finder.execute).to be_empty
+      end
+    end
+  end
+end

spec/helpers/dashboard_helper_spec.rb

+require 'spec_helper'
+
+describe DashboardHelper do
+  let(:user) { build(:user) }
+
+  before do
+    allow(helper).to receive(:current_user).and_return(user)
+    allow(helper).to receive(:can?) { true }
+  end
+
+  describe '#dashboard_nav_links' do
+    it 'has all the expected links by default' do
+      menu_items = [:projects, :groups, :activity, :milestones, :snippets]
+
+      expect(helper.dashboard_nav_links).to contain_exactly(*menu_items)
+    end
+
+    it 'does not contain cross project elements when the user cannot read cross project' do
+      expect(helper).to receive(:can?).with(user, :read_cross_project) { false }
+
+      expect(helper.dashboard_nav_links).not_to include(:activity, :milestones)
+    end
+  end
+end

spec/helpers/explore_helper_spec.rb

+require 'spec_helper'
+
+describe ExploreHelper do
+  let(:user) { build(:user) }
+
+  before do
+    allow(helper).to receive(:current_user).and_return(user)
+    allow(helper).to receive(:can?) { true }
+  end
+
+  describe '#explore_nav_links' do
+    it 'has all the expected links by default' do
+      menu_items = [:projects, :groups, :snippets]
+
+      expect(helper.explore_nav_links).to contain_exactly(*menu_items)
+    end
+  end
+end

spec/helpers/groups_helper_spec.rb

@@ -201,4 +201,39 @@ describe GroupsHelper do
       end
     end
   end
+
+  describe '#group_sidebar_links' do
+    let(:group) { create(:group, :public) }
+    let(:user) { create(:user) }
+    before do
+      allow(helper).to receive(:current_user) { user }
+      allow(helper).to receive(:can?) { true }
+      helper.instance_variable_set(:@group, group)
+    end
+
+    it 'returns all the expected links' do
+      links = [
+        :overview, :activity, :issues, :labels, :milestones, :merge_requests,
+        :group_members, :settings
+      ]
+
+      expect(helper.group_sidebar_links).to include(*links)
+    end
+
+    it 'includes settings when the user can admin the group' do
+      expect(helper).to receive(:current_user) { user }
+      expect(helper).to receive(:can?).with(user, :admin_group, group) { false }
+
+      expect(helper.group_sidebar_links).not_to include(:settings)
+    end
+
+    it 'excludes cross project features when the user cannot read cross project' do
+      cross_project_features = [:activity, :issues, :labels, :milestones,
+                                :merge_requests]
+
+      expect(helper).to receive(:can?).with(user, :read_cross_project) { false }
+
+      expect(helper.group_sidebar_links).not_to include(*cross_project_features)
+    end
+  end
 end

spec/helpers/issues_helper_spec.rb

@@ -113,21 +113,6 @@ describe IssuesHelper do
     end
   end
 
-  describe "milestone_options" do
-    it "gets closed milestone from current issue" do
-      closed_milestone = create(:closed_milestone, project: project)
-      milestone1       = create(:milestone, project: project)
-      milestone2       = create(:milestone, project: project)
-      issue.update_attributes(milestone_id: closed_milestone.id)
-
-      options = milestone_options(issue)
-
-      expect(options).to have_selector('option[selected]', text: closed_milestone.title)
-      expect(options).to have_selector('option', text: milestone1.title)
-      expect(options).to have_selector('option', text: milestone2.title)
-    end
-  end
-
   describe "#link_to_discussions_to_resolve" do
     describe "passing only a merge request" do
       let(:merge_request) { create(:merge_request) }

spec/helpers/nav_helper_spec.rb

+require 'spec_helper'
+
+describe NavHelper do
+  describe '#header_links' do
+    before do
+      allow(helper).to receive(:session) { {} }
+    end
+
+    context 'when the user is logged in' do
+      let(:user) { build(:user) }
+
+      before do
+        allow(helper).to receive(:current_user).and_return(user)
+        allow(helper).to receive(:can?) { true }
+      end
+
+      it 'has all the expected links by default' do
+        menu_items = [:user_dropdown, :search, :issues, :merge_requests, :todos]
+
+        expect(helper.header_links).to contain_exactly(*menu_items)
+      end
+
+      it 'contains the impersonation link while impersonating' do
+        expect(helper).to receive(:session) { { impersonator_id: 1 } }
+
+        expect(helper.header_links).to include(:admin_impersonation)
+      end
+
+      context 'when the user cannot read cross project' do
+        before do
+          allow(helper).to receive(:can?).with(user, :read_cross_project) { false }
+        end
+
+        it 'does not contain cross project elements when the user cannot read cross project' do
+          expect(helper.header_links).not_to include(:issues, :merge_requests, :todos, :search)
+        end
+
+        it 'shows the search box when the user cannot read cross project and he is visiting a project' do
+          helper.instance_variable_set(:@project, create(:project))
+
+          expect(helper.header_links).to include(:search)
+        end
+      end
+    end
+
+    it 'returns only the sign in and search when the user is not logged in' do
+      allow(helper).to receive(:current_user).and_return(nil)
+      allow(helper).to receive(:can?).with(nil, :read_cross_project) { true }
+
+      expect(helper.header_links).to contain_exactly(:sign_in, :search)
+    end
+  end
+end

spec/helpers/projects_helper_spec.rb

@@ -75,6 +75,12 @@ describe ProjectsHelper do
 
   describe "#project_list_cache_key", :clean_gitlab_redis_shared_state do
     let(:project) { create(:project, :repository) }
+    let(:user) { create(:user) }
+
+    before do
+      allow(helper).to receive(:current_user).and_return(user)
+      allow(helper).to receive(:can?).with(user, :read_cross_project) { true }
+    end
 
     it "includes the route" do
       expect(helper.project_list_cache_key(project)).to include(project.route.cache_key)
@@ -106,6 +112,10 @@ describe ProjectsHelper do
       expect(helper.project_list_cache_key(project).last).to start_with('v')
     end
 
+    it 'includes wether or not the user can read cross project' do
+      expect(helper.project_list_cache_key(project)).to include('cross-project:true')
+    end
+
     it "includes the pipeline status when there is a status" do
       create(:ci_pipeline, :success, project: project, sha: project.commit.sha)
 

spec/helpers/users_helper_spec.rb

@@ -14,4 +14,17 @@ describe UsersHelper do
       is_expected.to include("title=\"#{user.email}\"")
     end
   end
+
+  describe '#profile_tabs' do
+    subject(:tabs) { helper.profile_tabs }
+
+    before do
+      allow(helper).to receive(:current_user).and_return(user)
+      allow(helper).to receive(:can?).and_return(true)
+    end
+
+    it 'includes all the expected tabs' do
+      expect(tabs).to include(:activity, :groups, :contributed, :projects, :snippets)
+    end
+  end
 end

spec/lib/banzai/commit_renderer_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe Banzai::CommitRenderer do
   describe '.render' do
     it 'renders a commit description and title' do
-      user = double(:user)
+      user = build(:user)
       project = create(:project, :repository)
 
       expect(Banzai::ObjectRenderer).to receive(:new).with(project, user).and_call_original

spec/lib/banzai/filter/cross_project_issuable_information_filter_spec.rb

+require 'spec_helper'
+
+describe Banzai::Filter::CrossProjectIssuableInformationFilter do
+  include ActionView::Helpers::UrlHelper
+  include FilterSpecHelper
+
+  let(:user) { create(:user) }
+  let(:project) { create(:project, :public) }
+  let(:context) { { project: project, current_user: user } }
+  let(:other_project) { create(:project, :public) }
+
+  def create_link(issuable)
+    type = issuable.class.name.underscore.downcase
+    link_to(issuable.to_reference, '',
+            class: 'gfm has-tooltip',
+            title: issuable.title,
+            data: {
+              reference_type: type,
+              "#{type}": issuable.id
+            })
+  end
+
+  context 'when the user cannot read cross project' do
+    before do
+      allow(Ability).to receive(:allowed?) { false }
+    end
+
+    it 'skips links to issues within the same project' do
+      issue = create(:issue, project: project)
+      link = create_link(issue)
+      doc = filter(link, context)
+
+      result = doc.css('a').last
+
+      expect(result['class']).to include('has-tooltip')
+      expect(result['title']).to eq(issue.title)
+    end
+
+    it 'removes info from a cross project reference' do
+      issue = create(:issue, project: other_project)
+      link = create_link(issue)
+      doc = filter(link, context)
+
+      result = doc.css('a').last
+
+      expect(result['class']).not_to include('has-tooltip')
+      expect(result['title']).to be_empty
+    end
+  end
+end

spec/lib/banzai/filter/issuable_state_filter_spec.rb

@@ -77,6 +77,14 @@ describe Banzai::Filter::IssuableStateFilter do
     expect(doc.css('a').last.text).to eq("#{closed_issue.to_reference(other_project)} (closed)")
   end
 
+  it 'skips cross project references if the user cannot read cross project' do
+    expect(Ability).to receive(:allowed?).with(user, :read_cross_project) { false }
+    link = create_link(closed_issue.to_reference(other_project), issue: closed_issue.id, reference_type: 'issue')
+    doc = filter(link, context.merge(project: other_project))
+
+    expect(doc.css('a').last.text).to eq("#{closed_issue.to_reference(other_project)}")
+  end
+
   it 'does not append state when filter is not enabled' do
     link = create_link('text', issue: closed_issue.id, reference_type: 'issue')
     context = { current_user: user }

spec/lib/banzai/redactor_spec.rb

 require 'spec_helper'
 
 describe Banzai::Redactor do
-  let(:user) { build(:user) }
+  let(:user) { create(:user) }
   let(:project) { build(:project) }
   let(:redactor) { described_class.new(project, user) }
 

spec/lib/banzai/reference_parser/issue_parser_spec.rb

@@ -32,6 +32,45 @@ describe Banzai::ReferenceParser::IssueParser do
 
         expect(subject.nodes_visible_to_user(user, [link])).to eq([])
       end
+
+      context 'when the user cannot read cross project' do
+        let(:issue) { create(:issue) }
+
+        before do
+          allow(Ability).to receive(:allowed?).with(user, :read_cross_project) { false }
+          allow(Ability).to receive(:allowed?).with(user, :read_cross_project, :global) { false }
+        end
+
+        it 'returns the nodes when the user can read the issue' do
+          expect(Ability).to receive(:allowed?)
+                               .with(user, :read_issue_iid, issue)
+                               .and_return(true)
+
+          expect(subject.nodes_visible_to_user(user, [link])).to eq([link])
+        end
+
+        it 'returns an empty Array when the user can not read the issue' do
+          expect(Ability).to receive(:allowed?)
+                               .with(user, :read_issue_iid, issue)
+                               .and_return(false)
+
+          expect(subject.nodes_visible_to_user(user, [link])).to eq([])
+        end
+
+        context 'when the issue is not cross project' do
+          let(:issue) { create(:issue, project: project) }
+
+          it 'does not check `can_read_reference` if the issue is not cross project' do
+            expect(Ability).to receive(:issues_readable_by_user)
+                                 .with([issue], user)
+                                 .and_return([])
+
+            expect(subject).not_to receive(:can_read_reference?).with(user, issue)
+
+            expect(subject.nodes_visible_to_user(user, [link])).to eq([])
+          end
+        end
+      end
     end
 
     context 'when the link does not have a data-issue attribute' do

spec/lib/gitlab/contributions_calendar_spec.rb

@@ -118,6 +118,19 @@ describe Gitlab::ContributionsCalendar do
       expect(calendar.events_by_date(today)).to contain_exactly(e1)
       expect(calendar(contributor).events_by_date(today)).to contain_exactly(e1, e2, e3)
     end
+
+    context 'when the user cannot read read cross project' do
+      before do
+        allow(Ability).to receive(:allowed?).and_call_original
+        expect(Ability).to receive(:allowed?).with(user, :read_cross_project) { false }
+      end
+
+      it 'does not return any events' do
+        create_event(public_project, today)
+
+        expect(calendar(user).events_by_date(today)).to be_empty
+      end
+    end
   end
 
   describe '#starting_year' do

spec/lib/gitlab/cross_project_access/check_collection_spec.rb

+require 'spec_helper'
+
+describe Gitlab::CrossProjectAccess::CheckCollection do
+  subject(:collection) { described_class.new }
+
+  describe '#add_collection' do
+    it 'merges the checks of 2 collections' do
+      initial_check = double('check')
+      collection.add_check(initial_check)
+
+      other_collection = described_class.new
+      other_check = double('other_check')
+      other_collection.add_check(other_check)
+
+      shared_check = double('shared check')
+      other_collection.add_check(shared_check)
+      collection.add_check(shared_check)
+
+      collection.add_collection(other_collection)
+
+      expect(collection.checks).to contain_exactly(initial_check, shared_check, other_check)
+    end
+  end
+
+  describe '#should_run?' do
+    def fake_check(run, skip)
+      check = double("Check: run=#{run} - skip={skip}")
+      allow(check).to receive(:should_run?).and_return(run)
+      allow(check).to receive(:should_skip?).and_return(skip)
+      allow(check).to receive(:skip).and_return(skip)
+
+      check
+    end
+
+    it 'returns true if one of the check says it should run' do
+      check = fake_check(true, false)
+      other_check = fake_check(false, false)
+
+      collection.add_check(check)
+      collection.add_check(other_check)
+
+      expect(collection.should_run?(double)).to be_truthy
+    end
+
+    it 'returns false if one of the check says it should be skipped' do
+      check = fake_check(true, false)
+      other_check = fake_check(false, true)
+
+      collection.add_check(check)
+      collection.add_check(other_check)
+
+      expect(collection.should_run?(double)).to be_falsey
+    end
+  end
+end