Use CTEs for nested groups and authorizations

This commit introduces the usage of Common Table Expressions (CTEs) to
efficiently retrieve nested group hierarchies, without having to rely on
the "routes" table (which is an _incredibly_ inefficient way of getting
the data). This requires a patch to ActiveRecord (found in the added
initializer) to work properly as ActiveRecord doesn't support WITH
statements properly out of the box.

Unfortunately MySQL provides no efficient way of getting nested groups.
For example, the old routes setup could easily take 5-10 seconds
depending on the amount of "routes" in a database. Providing vastly
different logic for both MySQL and PostgreSQL will negatively impact the
development process. Because of this the various nested groups related
methods return empty relations when used in combination with MySQL.

For project authorizations the logic is split up into two classes:

* Gitlab::ProjectAuthorizations::WithNestedGroups
* Gitlab::ProjectAuthorizations::WithoutNestedGroups

Both classes get the fresh project authorizations (= as they should be
in the "project_authorizations" table), including nested groups if
PostgreSQL is used. The logic of these two classes is quite different
apart from their public interface. This complicates development a bit,
but unfortunately there is no way around this.

This commit also introduces Gitlab::GroupHierarchy. This class can be
used to get the ancestors and descendants of a base relation, or both by
using a UNION. This in turn is used by methods such as:

* Namespace#ancestors
* Namespace#descendants
* User#all_expanded_groups

Again this class relies on CTEs and thus only works on PostgreSQL. The
Namespace methods will return an empty relation when MySQL is used,
while User#all_expanded_groups will return only the groups a user is a
direct member of.

Performance wise the impact is quite large. For example, on GitLab.com
Namespace#descendants used to take around 580 ms to retrieve data for a
particular user. Using CTEs we are able to reduce this down to roughly 1
millisecond, returning the exact same data.

== On The Fly Refreshing

Refreshing of authorizations on the fly (= when
users.authorized_projects_populated was not set) is removed with this
commit. This simplifies the code, and ensures any queries used for
authorizations are not mutated because they are executed in a Rails
scope (e.g. Project.visible_to_user).

This commit includes a migration to schedule refreshing authorizations
for all users, ensuring all of them have their authorizations in place.
Said migration schedules users in batches of 5000, with 5 minutes
between every batch to smear the load around a bit.

== Spec Changes

This commit also introduces some changes to various specs. For example,
some specs for ProjectTeam assumed that creating a personal project
would _not_ lead to the owner having access, which is incorrect. Because
we also no longer refresh authorizations on the fly for new users some
code had to be added to the "empty_project" factory. This chunk of code
ensures that the owner's permissions are refreshed after creating the
project, something that is normally done in Projects::CreateService.

app/models/concerns/routable.rb

@@ -84,89 +84,6 @@ module Routable
         joins(:route).where(wheres.join(' OR '))
       end
     end
-
-    # Builds a relation to find multiple objects that are nested under user membership
-    #
-    # Usage:
-    #
-    #     Klass.member_descendants(1)
-    #
-    # Returns an ActiveRecord::Relation.
-    def member_descendants(user_id)
-      joins(:route).
-        joins("INNER JOIN routes r2 ON routes.path LIKE CONCAT(r2.path, '/%')
-               INNER JOIN members ON members.source_id = r2.source_id
-               AND members.source_type = r2.source_type").
-        where('members.user_id = ?', user_id)
-    end
-
-    # Builds a relation to find multiple objects that are nested under user
-    # membership. Includes the parent, as opposed to `#member_descendants`
-    # which only includes the descendants.
-    #
-    # Usage:
-    #
-    #     Klass.member_self_and_descendants(1)
-    #
-    # Returns an ActiveRecord::Relation.
-    def member_self_and_descendants(user_id)
-      joins(:route).
-        joins("INNER JOIN routes r2 ON routes.path LIKE CONCAT(r2.path, '/%')
-               OR routes.path = r2.path
-               INNER JOIN members ON members.source_id = r2.source_id
-               AND members.source_type = r2.source_type").
-        where('members.user_id = ?', user_id)
-    end
-
-    # Returns all objects in a hierarchy, where any node in the hierarchy is
-    # under the user membership.
-    #
-    # Usage:
-    #
-    #     Klass.member_hierarchy(1)
-    #
-    # Examples:
-    #
-    #     Given the following group tree...
-    #
-    #            _______group_1_______
-    #           |                     |
-    #           |                     |
-    #     nested_group_1        nested_group_2
-    #           |                     |
-    #           |                     |
-    #     nested_group_1_1      nested_group_2_1
-    #
-    #
-    #     ... the following results are returned:
-    #
-    #     * the user is a member of group 1
-    #       => 'group_1',
-    #          'nested_group_1', nested_group_1_1',
-    #          'nested_group_2', 'nested_group_2_1'
-    #
-    #     * the user is a member of nested_group_2
-    #       => 'group1',
-    #          'nested_group_2', 'nested_group_2_1'
-    #
-    #     * the user is a member of nested_group_2_1
-    #       => 'group1',
-    #          'nested_group_2', 'nested_group_2_1'
-    #
-    # Returns an ActiveRecord::Relation.
-    def member_hierarchy(user_id)
-      paths = member_self_and_descendants(user_id).pluck('routes.path')
-
-      return none if paths.empty?
-
-      wheres = paths.map do |path|
-        "#{connection.quote(path)} = routes.path
-         OR
-         #{connection.quote(path)} LIKE CONCAT(routes.path, '/%')"
-      end
-
-      joins(:route).where(wheres.join(' OR '))
-    end
   end
   def full_name

app/models/concerns/select_for_project_authorization.rb

@@ -3,7 +3,11 @@ module SelectForProjectAuthorization
   module ClassMethods
     def select_for_project_authorization
-      select("members.user_id, projects.id AS project_id, members.access_level")
+      select("projects.id AS project_id, members.access_level")
+    end
+
+    def select_as_master_for_project_authorization
+      select(["projects.id AS project_id", "#{Gitlab::Access::MASTER} AS access_level"])
     end
   end
 end

app/models/group.rb

@@ -38,6 +38,10 @@ class Group < Namespace
   after_save :update_two_factor_requirement
   class << self
+    def supports_nested_groups?
+      Gitlab::Database.postgresql?
+    end
+
     # Searches for groups matching the given query.
     #
     # This method uses ILIKE on PostgreSQL and LIKE on MySQL.
@@ -78,7 +82,7 @@ class Group < Namespace
       if current_scope.joins_values.include?(:shared_projects)
         joins('INNER JOIN namespaces project_namespace ON project_namespace.id = projects.namespace_id')
           .where('project_namespace.share_with_group_lock = ?',  false)
-          .select("members.user_id, projects.id AS project_id, LEAST(project_group_links.group_access, members.access_level) AS access_level")
+          .select("projects.id AS project_id, LEAST(project_group_links.group_access, members.access_level) AS access_level")
       else
         super
       end

app/models/namespace.rb

@@ -176,26 +176,22 @@ class Namespace < ActiveRecord::Base
     projects.with_shared_runners.any?
   end
-  # Scopes the model on ancestors of the record
+  # Returns all the ancestors of the current namespaces.
   def ancestors
-    if parent_id
-      path = route ? route.path : full_path
-      paths = []
-      until path.blank?
-        path = path.rpartition('/').first
-        paths << path
-      end
-
-      self.class.joins(:route).where('routes.path IN (?)', paths).reorder('routes.path ASC')
-    else
-      self.class.none
-    end
+    return self.class.none if !Group.supports_nested_groups? || !parent_id
+    Gitlab::GroupHierarchy.
+      new(self.class.where(id: parent_id)).
+      base_and_ancestors
   end
-  # Scopes the model on direct and indirect children of the record
+  # Returns all the descendants of the current namespace.
   def descendants
-    self.class.joins(:route).merge(Route.inside_path(route.path)).reorder('routes.path ASC')
+    return self.class.none unless Group.supports_nested_groups?
+
+    Gitlab::GroupHierarchy.
+      new(self.class.where(parent_id: id)).
+      base_and_descendants
   end
   def user_ids_for_project_authorizations

app/models/project_authorization.rb

@@ -6,6 +6,12 @@ class ProjectAuthorization < ActiveRecord::Base
   validates :access_level, inclusion: { in: Gitlab::Access.all_values }, presence: true
   validates :user, uniqueness: { scope: [:project, :access_level] }, presence: true
+  def self.select_from_union(union)
+    select(['project_id', 'MAX(access_level) AS access_level']).
+      from("(#{union.to_sql}) #{ProjectAuthorization.table_name}").
+      group(:project_id)
+  end
+
   def self.insert_authorizations(rows, per_batch = 1000)
     rows.each_slice(per_batch) do |slice|
       tuples = slice.map do |tuple|

app/models/user.rb

@@ -10,9 +10,12 @@ class User < ActiveRecord::Base
   include Sortable
   include CaseSensitivity
   include TokenAuthenticatable
+  include IgnorableColumn
   DEFAULT_NOTIFICATION_LEVEL = :participating
+  ignore_column :authorized_projects_populated
+
   add_authentication_token_field :authentication_token
   add_authentication_token_field :incoming_email_token
@@ -212,7 +215,6 @@ class User < ActiveRecord::Base
   scope :blocked, -> { with_states(:blocked, :ldap_blocked) }
   scope :external, -> { where(external: true) }
   scope :active, -> { with_state(:active).non_internal }
-  scope :not_in_project, ->(project) { project.users.present? ? where("id not in (:ids)", ids: project.users.map(&:id) ) : all }
   scope :without_projects, -> { where('id NOT IN (SELECT DISTINCT(user_id) FROM members WHERE user_id IS NOT NULL AND requested_at IS NULL)') }
   scope :todo_authors, ->(user_id, state) { where(id: Todo.where(user_id: user_id, state: state).select(:author_id)) }
   scope :order_recent_sign_in, -> { reorder(Gitlab::Database.nulls_last_order('last_sign_in_at', 'DESC')) }
@@ -504,23 +506,18 @@ class User < ActiveRecord::Base
     Group.where("namespaces.id IN (#{union.to_sql})")
   end
-  def nested_groups
-    Group.member_descendants(id)
-  end
-
+  # Returns a relation of groups the user has access to, including their parent
+  # and child groups (recursively).
   def all_expanded_groups
-    Group.member_hierarchy(id)
+    return groups unless Group.supports_nested_groups?
+
+    Gitlab::GroupHierarchy.new(groups).all_groups
   end
   def expanded_groups_requiring_two_factor_authentication
     all_expanded_groups.where(require_two_factor_authentication: true)
   end
-  def nested_groups_projects
-    Project.joins(:namespace).where('namespaces.parent_id IS NOT NULL').
-      member_descendants(id)
-  end
-
   def refresh_authorized_projects
     Users::RefreshAuthorizedProjectsService.new(self).execute
   end
@@ -529,18 +526,15 @@ class User < ActiveRecord::Base
     project_authorizations.where(project_id: project_ids).delete_all
   end
-  def set_authorized_projects_column
-    unless authorized_projects_populated
-      update_column(:authorized_projects_populated, true)
-    end
-  end
-
   def authorized_projects(min_access_level = nil)
-    refresh_authorized_projects unless authorized_projects_populated
-
-    # We're overriding an association, so explicitly call super with no arguments or it would be passed as `force_reload` to the association
+    # We're overriding an association, so explicitly call super with no
+    # arguments or it would be passed as `force_reload` to the association
     projects = super()
-    projects = projects.where('project_authorizations.access_level >= ?', min_access_level) if min_access_level
+
+    if min_access_level
+      projects = projects.
+        where('project_authorizations.access_level >= ?', min_access_level)
+    end
     projects
   end

app/services/users/refresh_authorized_projects_service.rb

@@ -73,12 +73,11 @@ module Users
     # remove - The IDs of the authorization rows to remove.
     # add - Rows to insert in the form `[user id, project id, access level]`
     def update_authorizations(remove = [], add = [])
-      return if remove.empty? && add.empty? && user.authorized_projects_populated
+      return if remove.empty? && add.empty?
       User.transaction do
         user.remove_project_authorizations(remove) unless remove.empty?
         ProjectAuthorization.insert_authorizations(add) unless add.empty?
-        user.set_authorized_projects_column
       end
       # Since we batch insert authorization rows, Rails' associations may get
@@ -101,38 +100,13 @@ module Users
     end
     def fresh_authorizations
-      ProjectAuthorization.
-        unscoped.
-        select('project_id, MAX(access_level) AS access_level').
-        from("(#{project_authorizations_union.to_sql}) #{ProjectAuthorization.table_name}").
-        group(:project_id)
-    end
-
-    private
-
-    # Returns a union query of projects that the user is authorized to access
-    def project_authorizations_union
-      relations = [
-        # Personal projects
-        user.personal_projects.select("#{user.id} AS user_id, projects.id AS project_id, #{Gitlab::Access::MASTER} AS access_level"),
-
-        # Projects the user is a member of
-        user.projects.select_for_project_authorization,
-
-        # Projects of groups the user is a member of
-        user.groups_projects.select_for_project_authorization,
-
-        # Projects of subgroups of groups the user is a member of
-        user.nested_groups_projects.select_for_project_authorization,
-
-        # Projects shared with groups the user is a member of
-        user.groups.joins(:shared_projects).select_for_project_authorization,
-
-        # Projects shared with subgroups of groups the user is a member of
-        user.nested_groups.joins(:shared_projects).select_for_project_authorization
-      ]
-      Gitlab::SQL::Union.new(relations)
+      klass = if Group.supports_nested_groups?
+                Gitlab::ProjectAuthorizations::WithNestedGroups
+              else
+                Gitlab::ProjectAuthorizations::WithoutNestedGroups
+              end
+      klass.new(user).calculate
     end
   end
 end

config/initializers/postgresql_cte.rb

+# Adds support for WITH statements when using PostgreSQL. The code here is taken
+# from https://github.com/shmay/ctes_in_my_pg which at the time of writing has
+# not been pushed to RubyGems. The license of this repository is as follows:
+#
+# The MIT License (MIT)
+#
+# Copyright (c) 2012 Dan McClain
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+module ActiveRecord
+  class Relation
+    class Merger # :nodoc:
+      def normal_values
+        NORMAL_VALUES + [:with]
+      end
+    end
+  end
+end
+
+module ActiveRecord::Querying
+  delegate :with, to: :all
+end
+
+module ActiveRecord
+  class Relation
+    # WithChain objects act as placeholder for queries in which #with does not have any parameter.
+    # In this case, #with must be chained with #recursive to return a new relation.
+    class WithChain
+      def initialize(scope)
+        @scope = scope
+      end
+
+      # Returns a new relation expressing WITH RECURSIVE
+      def recursive(*args)
+        @scope.with_values += args
+        @scope.recursive_value = true
+        @scope
+      end
+    end
+
+    def with_values
+      @values[:with] || []
+    end
+
+    def with_values=(values)
+      raise ImmutableRelation if @loaded
+      @values[:with] = values
+    end
+
+    def recursive_value=(value)
+      raise ImmutableRelation if @loaded
+      @values[:recursive] = value
+    end
+
+    def recursive_value
+      @values[:recursive]
+    end
+
+    def with(opts = :chain, *rest)
+      if opts == :chain
+        WithChain.new(spawn)
+      elsif opts.blank?
+        self
+      else
+        spawn.with!(opts, *rest)
+      end
+    end
+
+    def with!(opts = :chain, *rest) # :nodoc:
+      if opts == :chain
+        WithChain.new(self)
+      else
+        self.with_values += [opts] + rest
+        self
+      end
+    end
+
+    def build_arel
+      arel = super()
+
+      build_with(arel) if @values[:with]
+
+      arel
+    end
+
+    def build_with(arel)
+      with_statements = with_values.flat_map do |with_value|
+        case with_value
+        when String
+          with_value
+        when Hash
+          with_value.map  do |name, expression|
+            case expression
+            when String
+              select = Arel::Nodes::SqlLiteral.new "(#{expression})"
+            when ActiveRecord::Relation, Arel::SelectManager
+              select = Arel::Nodes::SqlLiteral.new "(#{expression.to_sql})"
+            end
+            Arel::Nodes::As.new Arel::Nodes::SqlLiteral.new("\"#{name}\""), select
+          end
+        when Arel::Nodes::As
+          with_value
+        end
+      end
+
+      unless with_statements.empty?
+        if recursive_value
+          arel.with :recursive, with_statements
+        else
+          arel.with with_statements
+        end
+      end
+    end
+  end
+end

db/migrate/20170503140201_reschedule_project_authorizations.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RescheduleProjectAuthorizations < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class User < ActiveRecord::Base
+    self.table_name = 'users'
+  end
+
+  def up
+    offset = 0
+    batch = 5000
+    start = Time.now
+
+    loop do
+      relation = User.where('id > ?', offset)
+      user_ids = relation.limit(batch).reorder(id: :asc).pluck(:id)
+
+      break if user_ids.empty?
+
+      offset = user_ids.last
+
+      # This will schedule each batch 5 minutes after the previous batch was
+      # scheduled. This smears out the load over time, instead of immediately
+      # scheduling a million jobs.
+      Sidekiq::Client.push_bulk(
+        'queue' => 'authorized_projects',
+        'args' => user_ids.zip,
+        'class' => 'AuthorizedProjectsWorker',
+        'at' => start.to_i
+      )
+
+      start += 5.minutes
+    end
+  end
+
+  def down
+  end
+end

db/post_migrate/20170503120310_remove_users_authorized_projects_populated.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveUsersAuthorizedProjectsPopulated < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def change
+    remove_column :users, :authorized_projects_populated, :boolean
+  end
+end

db/schema.rb

@@ -1352,7 +1352,6 @@ ActiveRecord::Schema.define(version: 20170508190732) do
     t.boolean "external", default: false
     t.string "incoming_email_token"
     t.string "organization"
-    t.boolean "authorized_projects_populated"
     t.boolean "require_two_factor_authentication_from_group", default: false, null: false
     t.integer "two_factor_grace_period", default: 48, null: false
     t.boolean "ghost"

lib/gitlab/group_hierarchy.rb

+module Gitlab
+  # Retrieving of parent or child groups based on a base ActiveRecord relation.
+  #
+  # This class uses recursive CTEs and as a result will only work on PostgreSQL.
+  class GroupHierarchy
+    attr_reader :base, :model
+
+    # base - An instance of ActiveRecord::Relation for which to get parent or
+    #        child groups.
+    def initialize(base)
+      @base = base
+      @model = base.model
+    end
+
+    # Returns a relation that includes the base set of groups and all their
+    # ancestors (recursively).
+    def base_and_ancestors
+      base_and_ancestors_cte.apply_to(model.all)
+    end
+
+    # Returns a relation that includes the base set of groups and all their
+    # descendants (recursively).
+    def base_and_descendants
+      base_and_descendants_cte.apply_to(model.all)
+    end
+
+    # Returns a relation that includes the base groups, their ancestors, and the
+    # descendants of the base groups.
+    #
+    # The resulting query will roughly look like the following:
+    #
+    #     WITH RECURSIVE ancestors AS ( ... ),
+    #       descendants AS ( ... )
+    #     SELECT *
+    #     FROM (
+    #       SELECT *
+    #       FROM ancestors namespaces
+    #
+    #       UNION
+    #
+    #       SELECT *
+    #       FROM descendants namespaces
+    #     ) groups;
+    #
+    # Using this approach allows us to further add criteria to the relation with
+    # Rails thinking it's selecting data the usual way.
+    def all_groups
+      ancestors = base_and_ancestors_cte
+      descendants = base_and_descendants_cte
+
+      ancestors_table = ancestors.alias_to(groups_table)
+      descendants_table = descendants.alias_to(groups_table)
+
+      union = SQL::Union.new([model.unscoped.from(ancestors_table),
+                              model.unscoped.from(descendants_table)])
+
+      model.
+        unscoped.
+        with.
+        recursive(ancestors.to_arel, descendants.to_arel).
+        from("(#{union.to_sql}) #{model.table_name}")
+    end
+
+    private
+
+    def base_and_ancestors_cte
+      cte = SQL::RecursiveCTE.new(:base_and_ancestors)
+
+      cte << base.except(:order)
+
+      # Recursively get all the ancestors of the base set.
+      cte << model.
+        from([groups_table, cte.table]).
+        where(groups_table[:id].eq(cte.table[:parent_id])).
+        except(:order)
+
+      cte
+    end
+
+    def base_and_descendants_cte
+      cte = SQL::RecursiveCTE.new(:base_and_descendants)
+
+      cte << base.except(:order)
+
+      # Recursively get all the descendants of the base set.
+      cte << model.
+        from([groups_table, cte.table]).
+        where(groups_table[:parent_id].eq(cte.table[:id])).
+        except(:order)
+
+      cte
+    end
+
+    def groups_table
+      model.arel_table
+    end
+  end
+end

lib/gitlab/project_authorizations/with_nested_groups.rb

+module Gitlab
+  module ProjectAuthorizations
+    # Calculating new project authorizations when supporting nested groups.
+    #
+    # This class relies on Common Table Expressions to efficiently get all data,
+    # including data for nested groups. As a result this class can only be used
+    # on PostgreSQL.
+    class WithNestedGroups
+      attr_reader :user
+
+      # user - The User object for which to calculate the authorizations.
+      def initialize(user)
+        @user = user
+      end
+
+      def calculate
+        cte = recursive_cte
+        cte_alias = cte.table.alias(Group.table_name)
+        projects = Project.arel_table
+        links = ProjectGroupLink.arel_table
+
+        # These queries don't directly use the user object so they don't depend
+        # on the state of said object, ensuring the produced queries are always
+        # the same.
+        relations = [
+          # The project a user has direct access to.
+          user.projects.select_for_project_authorization,
+
+          # The personal projects of the user.
+          user.personal_projects.select_as_master_for_project_authorization,
+
+          # Projects that belong directly to any of the groups the user has
+          # access to.
+          Namespace.
+            unscoped.
+            select([alias_as_column(projects[:id], 'project_id'),
+                    cte_alias[:access_level]]).
+            from(cte_alias).
+            joins(:projects),
+
+          # Projects shared with any of the namespaces the user has access to.
+          Namespace.
+            unscoped.
+            select([links[:project_id],
+                    least(cte_alias[:access_level],
+                          links[:group_access],
+                          'access_level')]).
+            from(cte_alias).
+            joins('INNER JOIN project_group_links ON project_group_links.group_id = namespaces.id').
+            joins('INNER JOIN projects ON projects.id = project_group_links.project_id').
+            joins('INNER JOIN namespaces p_ns ON p_ns.id = projects.namespace_id').
+            where('p_ns.share_with_group_lock IS FALSE')
+        ]
+
+        union = Gitlab::SQL::Union.new(relations)
+
+        ProjectAuthorization.
+          unscoped.
+          with.
+          recursive(cte.to_arel).
+          select_from_union(union)
+      end
+
+      private
+
+      # Builds a recursive CTE that gets all the groups the current user has
+      # access to, including any nested groups.
+      def recursive_cte
+        cte = Gitlab::SQL::RecursiveCTE.new(:namespaces_cte)
+        members = Member.arel_table
+        namespaces = Namespace.arel_table
+
+        # Namespaces the user is a member of.
+        cte << user.groups.
+          select([namespaces[:id], members[:access_level]]).
+          except(:order)
+
+        # Sub groups of any groups the user is a member of.
+        cte << Group.select([namespaces[:id],
+                             greatest(members[:access_level],
+                                      cte.table[:access_level], 'access_level')]).
+          joins(join_cte(cte)).
+          joins(join_members).
+          except(:order)
+
+        cte
+      end
+
+      # Builds a LEFT JOIN to join optional memberships onto the CTE.
+      def join_members
+        members = Member.arel_table
+        namespaces = Namespace.arel_table
+
+        cond = members[:source_id].
+          eq(namespaces[:id]).
+          and(members[:source_type].eq('Namespace')).
+          and(members[:requested_at].eq(nil)).
+          and(members[:user_id].eq(user.id))
+
+        Arel::Nodes::OuterJoin.new(members, Arel::Nodes::On.new(cond))
+      end
+
+      # Builds an INNER JOIN to join namespaces onto the CTE.
+      def join_cte(cte)
+        namespaces = Namespace.arel_table
+        cond = cte.table[:id].eq(namespaces[:parent_id])
+
+        Arel::Nodes::InnerJoin.new(cte.table, Arel::Nodes::On.new(cond))
+      end
+
+      def greatest(left, right, column_alias)
+        sql_function('GREATEST', [left, right], column_alias)
+      end
+
+      def least(left, right, column_alias)
+        sql_function('LEAST', [left, right], column_alias)
+      end
+
+      def sql_function(name, args, column_alias)
+        alias_as_column(Arel::Nodes::NamedFunction.new(name, args), column_alias)
+      end
+
+      def alias_as_column(value, alias_to)
+        Arel::Nodes::As.new(value, Arel::Nodes::SqlLiteral.new(alias_to))
+      end
+    end
+  end
+end

lib/gitlab/project_authorizations/without_nested_groups.rb

+module Gitlab
+  module ProjectAuthorizations
+    # Calculating new project authorizations when not supporting nested groups.
+    class WithoutNestedGroups
+      attr_reader :user
+
+      # user - The User object for which to calculate the authorizations.
+      def initialize(user)
+        @user = user
+      end
+
+      def calculate
+        relations = [
+          # Projects the user is a direct member of
+          user.projects.select_for_project_authorization,
+
+          # Personal projects
+          user.personal_projects.select_as_master_for_project_authorization,
+
+          # Projects of groups the user is a member of
+          user.groups_projects.select_for_project_authorization,
+
+          # Projects shared with groups the user is a member of
+          user.groups.joins(:shared_projects).select_for_project_authorization
+        ]
+
+        union = Gitlab::SQL::Union.new(relations)
+
+        ProjectAuthorization.
+          unscoped.
+          select_from_union(union)
+      end
+    end
+  end
+end

lib/gitlab/sql/recursive_cte.rb

+module Gitlab
+  module SQL
+    # Class for easily building recursive CTE statements.
+    #
+    # Example:
+    #
+    #     cte = RecursiveCTE.new(:my_cte_name)
+    #     ns = Arel::Table.new(:namespaces)
+    #
+    #     cte << Namespace.
+    #       where(ns[:parent_id].eq(some_namespace_id))
+    #
+    #     cte << Namespace.
+    #       from([ns, cte.table]).
+    #       where(ns[:parent_id].eq(cte.table[:id]))
+    #
+    #     Namespace.with.
+    #       recursive(cte.to_arel).
+    #       from(cte.alias_to(ns))
+    class RecursiveCTE
+      attr_reader :table
+
+      # name - The name of the CTE as a String or Symbol.
+      def initialize(name)
+        @table = Arel::Table.new(name)
+        @queries = []
+      end
+
+      # Adds a query to the body of the CTE.
+      #
+      # relation - The relation object to add to the body of the CTE.
+      def <<(relation)
+        @queries << relation
+      end
+
+      # Returns the Arel relation for this CTE.
+      def to_arel
+        sql = Arel::Nodes::SqlLiteral.new(Union.new(@queries).to_sql)
+
+        Arel::Nodes::As.new(table, Arel::Nodes::Grouping.new(sql))
+      end
+
+      # Returns an "AS" statement that aliases the CTE name as the given table
+      # name. This allows one to trick ActiveRecord into thinking it's selecting
+      # from an actual table, when in reality it's selecting from a CTE.
+      #
+      # alias_table - The Arel table to use as the alias.
+      def alias_to(alias_table)
+        Arel::Nodes::As.new(table, alias_table)
+      end
+
+      # Applies the CTE to the given relation, returning a new one that will
+      # query from it.
+      def apply_to(relation)
+        relation.except(:where).
+          with.
+          recursive(to_arel).
+          from(alias_to(relation.model.arel_table))
+      end
+    end
+  end
+end

spec/controllers/autocomplete_controller_spec.rb

@@ -22,7 +22,7 @@ describe AutocompleteController do
         let(:body) { JSON.parse(response.body) }
         it { expect(body).to be_kind_of(Array) }
-        it { expect(body.size).to eq 1 }
+        it { expect(body.size).to eq 2 }
         it { expect(body.map { |u| u["username"] }).to include(user.username) }
       end
@@ -80,8 +80,8 @@ describe AutocompleteController do
         end
         it { expect(body).to be_kind_of(Array) }
-        it { expect(body.size).to eq 2 }
-        it { expect(body.map { |u| u['username'] }).to match_array([user.username, non_member.username]) }
+        it { expect(body.size).to eq 3 }
+        it { expect(body.map { |u| u['username'] }).to include(user.username, non_member.username) }
       end
     end
@@ -108,7 +108,7 @@ describe AutocompleteController do
         end
         it { expect(body).to be_kind_of(Array) }
-        it { expect(body.size).to eq 1 }
+        it { expect(body.size).to eq 2 }
       end
       describe 'GET #users with project' do

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -2,7 +2,7 @@ require 'spec_helper'
 describe Projects::MergeRequestsController do
   let(:project) { create(:project) }
-  let(:user)    { create(:user) }
+  let(:user)    { project.owner }
   let(:merge_request) { create(:merge_request_with_diffs, target_project: project, source_project: project) }
   let(:merge_request_with_conflicts) do
     create(:merge_request, source_branch: 'conflict-resolvable', target_branch: 'conflict-start', source_project: project) do |mr|
@@ -12,7 +12,6 @@ describe Projects::MergeRequestsController do
   before do
     sign_in(user)
-    project.team << [user, :master]
   end
   describe 'GET new' do
@@ -292,6 +291,8 @@ describe Projects::MergeRequestsController do
     end
     context 'when user cannot access' do
+      let(:user) { create(:user) }
+
       before do
         project.add_reporter(user)
         xhr :post, :merge, base_params
@@ -448,6 +449,8 @@ describe Projects::MergeRequestsController do
   end
   describe "DELETE destroy" do
+    let(:user) { create(:user) }
+
     it "denies access to users unless they're admin or project owner" do
       delete :destroy, namespace_id: project.namespace, project_id: project, id: merge_request.iid

spec/factories/projects.rb

@@ -107,6 +107,18 @@ FactoryGirl.define do
           merge_requests_access_level: merge_requests_access_level,
           repository_access_level: evaluator.repository_access_level
         )
+
+      # Normally the class Projects::CreateService is used for creating
+      # projects, and this class takes care of making sure the owner and current
+      # user have access to the project. Our specs don't use said service class,
+      # thus we must manually refresh things here.
+      owner = project.owner
+
+      if owner && owner.is_a?(User) && !project.pending_delete
+        project.members.create!(user: owner, access_level: Gitlab::Access::MASTER)
+      end
+
+      project.group&.refresh_members_authorized_projects
     end
   end

spec/features/groups/group_name_toggle_spec.rb

@@ -22,7 +22,7 @@ feature 'Group name toggle', feature: true, js: true do
     expect(page).not_to have_css('.group-name-toggle')
   end
-  it 'is present if the title is longer than the container' do
+  it 'is present if the title is longer than the container', :nested_groups do
     visit group_path(nested_group_3)
     title_width = page.evaluate_script("$('.title')[0].offsetWidth")
@@ -35,7 +35,7 @@ feature 'Group name toggle', feature: true, js: true do
     expect(title_width).to be > container_width
   end
-  it 'should show the full group namespace when toggled' do
+  it 'should show the full group namespace when toggled', :nested_groups do
     page_height = page.current_window.size[1]
     page.current_window.resize_to(SMALL_SCREEN, page_height)
     visit group_path(nested_group_3)

spec/features/groups/members/list_spec.rb

@@ -12,7 +12,7 @@ feature 'Groups members list', feature: true do
     login_as(user1)
   end
-  scenario 'show members from current group and parent' do
+  scenario 'show members from current group and parent', :nested_groups do
     group.add_developer(user1)
     nested_group.add_developer(user2)
@@ -22,7 +22,7 @@ feature 'Groups members list', feature: true do
     expect(second_row.text).to include(user2.name)
   end
-  scenario 'show user once if member of both current group and parent' do
+  scenario 'show user once if member of both current group and parent', :nested_groups do
     group.add_developer(user1)
     nested_group.add_developer(user1)