diff --git a/app/models/group.rb b/app/models/group.rb
index 8e89c7ecfb1..9520db1bc0a 100644
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -63,6 +63,8 @@ class Group < Namespace
   after_save :update_two_factor_requirement
   after_update :path_changed_hook, if: :saved_change_to_path?
 
+  scope :with_users, -> { includes(:users) }
+
   class << self
     def sort_by_attribute(method)
       if method == 'storage_size_desc'
diff --git a/doc/user/project/code_owners.md b/doc/user/project/code_owners.md
index ae04616943f..c76847616b3 100644
--- a/doc/user/project/code_owners.md
+++ b/doc/user/project/code_owners.md
@@ -1,10 +1,12 @@
 # Code Owners **[STARTER]**
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6916)
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6916)
 in [GitLab Starter](https://about.gitlab.com/pricing/) 11.3.
+> - [Support for group namespaces](https://gitlab.com/gitlab-org/gitlab-ce/issues/53182) added in GitLab Starter 12.1.
 
-You can use a `CODEOWNERS` file to specify users that are responsible
-for certain files in a repository.
+You can use a `CODEOWNERS` file to specify users or
+[shared groups](members/share_project_with_groups.md)
+that are responsible for certain files in a repository.
 
 You can choose and add the `CODEOWNERS` file in three places:
 
@@ -25,7 +27,8 @@ the given file.
 
 Files can be specified using the same kind of patterns you would use
 in the `.gitignore` file followed by the `@username` or email of one
-or more users that should be owners of the file.
+or more users or by the `@name` of one or more groups that should
+be owners of the file.
 
 The order in which the paths are defined is significant: the last
 pattern that matches a given path will be used to find the code
@@ -63,6 +66,10 @@ CODEOWNERS @multiple @owners	@tab-separated
 # owner for the LICENSE file
 LICENSE @legal this_does_not_match janedoe@gitlab.com
 
+# Group names can be used to match groups and nested groups to specify
+# them as owners for a file
+README @group @group/with-nested/subgroup
+
 # Ending a path in a `/` will specify the code owners for every file
 # nested in that directory, on any level
 /docs/ @all-docs
diff --git a/lib/gitlab/user_extractor.rb b/lib/gitlab/user_extractor.rb
deleted file mode 100644
index ede60c9ab1d..00000000000
--- a/lib/gitlab/user_extractor.rb
+++ /dev/null
@@ -1,56 +0,0 @@
-# frozen_string_literal: true
-
-# This class extracts all users found in a piece of text by the username or the
-# email address
-
-module Gitlab
-  class UserExtractor
-    # Not using `Devise.email_regexp` to filter out any chars that an email
-    # does not end with and not pinning the email to a start of end of a string.
-    EMAIL_REGEXP = /(?<email>([^@\s]+@[^@\s]+(?<!\W)))/.freeze
-    USERNAME_REGEXP = User.reference_pattern
-
-    def initialize(text)
-      # EE passes an Array to `text` in a few places, so we want to support both
-      # here.
-      @text = Array(text).join(' ')
-    end
-
-    def users
-      return User.none unless @text.present?
-      return User.none if references.empty?
-
-      @users ||= User.from_union(union_relations)
-    end
-
-    def usernames
-      matches[:usernames]
-    end
-
-    def emails
-      matches[:emails]
-    end
-
-    def references
-      @references ||= matches.values.flatten
-    end
-
-    def matches
-      @matches ||= {
-        emails: @text.scan(EMAIL_REGEXP).flatten.uniq,
-        usernames: @text.scan(USERNAME_REGEXP).flatten.uniq
-      }
-    end
-
-    private
-
-    def union_relations
-      relations = []
-
-      relations << User.by_any_email(emails) if emails.any?
-      relations << User.by_username(usernames) if usernames.any?
-
-      relations
-    end
-  end
-end
diff --git a/spec/lib/gitlab/user_extractor_spec.rb b/spec/lib/gitlab/user_extractor_spec.rb
deleted file mode 100644
index b86ec5445b8..00000000000
--- a/spec/lib/gitlab/user_extractor_spec.rb
+++ /dev/null
@@ -1,78 +0,0 @@
-# frozen_string_literal: true
-
-require 'spec_helper'
-
-describe Gitlab::UserExtractor do
-  let(:text) do
-    <<~TXT
-    This is a long texth that mentions some users.
-    @user-1, @user-2 and user@gitlab.org take a walk in the park.
-    There they meet @user-4 that was out with other-user@gitlab.org.
-    @user-1 thought it was late, so went home straight away
-    TXT
-  end
-  subject(:extractor) { described_class.new(text) }
-
-  describe '#users' do
-    it 'returns an empty relation when nil was passed' do
-      extractor = described_class.new(nil)
-
-      expect(extractor.users).to be_empty
-      expect(extractor.users).to be_a(ActiveRecord::Relation)
-    end
-
-    it 'returns the user case insensitive for usernames' do
-      user = create(:user, username: "USER-4")
-
-      expect(extractor.users).to include(user)
-    end
-
-    it 'returns users by primary email' do
-      user = create(:user, email: 'user@gitlab.org')
-
-      expect(extractor.users).to include(user)
-    end
-
-    it 'returns users by secondary email' do
-      user = create(:email, email: 'other-user@gitlab.org').user
-
-      expect(extractor.users).to include(user)
-    end
-
-    context 'input as array of strings' do
-      it 'is treated as one string' do
-        extractor = described_class.new(text.lines)
-
-        user_1 = create(:user, username: "USER-1")
-        user_4 = create(:user, username: "USER-4")
-        user_email = create(:user, email: 'user@gitlab.org')
-
-        expect(extractor.users).to contain_exactly(user_1, user_4, user_email)
-      end
-    end
-  end
-
-  describe '#matches' do
-    it 'includes all mentioned email adresses' do
-      expect(extractor.matches[:emails]).to contain_exactly('user@gitlab.org', 'other-user@gitlab.org')
-    end
-
-    it 'includes all mentioned usernames' do
-      expect(extractor.matches[:usernames]).to contain_exactly('user-1', 'user-2', 'user-4')
-    end
-
-    context 'input has no matching e-mail or usernames' do
-      it 'returns an empty list of users' do
-        extractor = described_class.new('My test')
-
-        expect(extractor.users).to be_empty
-      end
-    end
-  end
-
-  describe '#references' do
-    it 'includes all user-references once' do
-      expect(extractor.references).to contain_exactly('user-1', 'user-2', 'user@gitlab.org', 'user-4', 'other-user@gitlab.org')
-    end
-  end
-end