Add repository languages for projects

Our friends at GitHub show the programming languages for a long time,
and inspired by that this commit means to create about the same
functionality.

Language detection is done through Linguist, as before, where the
difference is that we cache the result in the database. Also, Gitaly can
incrementaly scan a repository. This is done through a shell out, which
creates overhead of about 3s each run. For now this won't be improved.

Scans are triggered by pushed to the default branch, usually `master`.
However, one exception to this rule the charts page. If we're requesting
this expensive data anyway, we just cache it in the database.

Edge cases where there is no repository, or its empty are caught in the
Repository model. This makes use of Redis caching, which is probably
already loaded.

The added model is called RepositoryLanguage, which will make it harder
if/when GitLab supports multiple repositories per project. However, for
now I think this shouldn't be a concern. Also, Language could be
confused with the i18n languages and felt like the current name was
suiteable too.

Design of the Project#Show page is done with help from @dimitrieh. This
change is not visible to the end user unless detections are done.

29 files changed, 478 insertions, 4 deletions

diff --git a/app/assets/stylesheets/pages/projects.scss b/app/assets/stylesheets/pages/projects.scss
index aa83e5bdebc..2a41a045e71 100644
--- a/app/assets/stylesheets/pages/projects.scss
+++ b/app/assets/stylesheets/pages/projects.scss
@@ -754,6 +754,11 @@
   }
 }
 
+.repository-languages-bar {
+  height: 6px;
+  margin-bottom: 8px;
+}
+
 pre.light-well {
   border-color: $well-light-border;
 }
diff --git a/app/helpers/repository_languages_helper.rb b/app/helpers/repository_languages_helper.rb
new file mode 100644
index 00000000000..9a842cf5ce0
--- /dev/null
+++ b/app/helpers/repository_languages_helper.rb
@@ -0,0 +1,16 @@
+module RepositoryLanguagesHelper
+  def repository_languages_bar(languages)
+    return if languages.none?
+
+    content_tag :div, class: 'progress repository-languages-bar' do
+      safe_join(languages.map { |lang| language_progress(lang) })
+    end
+  end
+
+  def language_progress(lang)
+    content_tag :div, nil,
+      class: "progress-bar has-tooltip",
+      style: "width: #{lang.share}%; background-color:#{lang.color}",
+      title: lang.name
+  end
+end
diff --git a/app/models/namespace.rb b/app/models/namespace.rb
index c1dc2f55346..de06e080a7d 100644
--- a/app/models/namespace.rb
+++ b/app/models/namespace.rb
@@ -122,6 +122,7 @@ class Namespace < ActiveRecord::Base
   def to_param
     full_path
   end
+  alias_method :flipper_id, :to_param
 
   def human_name
     owner_name
diff --git a/app/models/programming_language.rb b/app/models/programming_language.rb
new file mode 100644
index 00000000000..400d6c407a7
--- /dev/null
+++ b/app/models/programming_language.rb
@@ -0,0 +1,4 @@
+class ProgrammingLanguage < ActiveRecord::Base
+  validates :name, presence: true
+  validates :color, allow_blank: false, color: true
+end
diff --git a/app/models/project.rb b/app/models/project.rb
index da30d2fbb4f..af32afc08e2 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -192,6 +192,7 @@ class Project < ActiveRecord::Base
   has_many :hooks, class_name: 'ProjectHook'
   has_many :protected_branches
   has_many :protected_tags
+  has_many :repository_languages, -> { order "share DESC" }
 
   has_many :project_authorizations
   has_many :authorized_users, through: :project_authorizations, source: :user, class_name: 'User'
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 50f42be661b..9a6281bc1f7 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -235,6 +235,12 @@ class Repository
     false
   end
 
+  def languages
+    return [] if empty?
+
+    raw_repository.languages(root_ref)
+  end
+
   # Makes sure a commit is kept around when Git garbage collection runs.
   # Git GC will delete commits from the repository that are no longer in any
   # branches or tags, but we want to keep some of these commits around, for
@@ -432,6 +438,8 @@ class Repository
   # Runs code after a repository has been forked/imported.
   def after_import
     expire_content_cache
+
+    DetectRepositoryLanguagesWorker.perform_async(project.id, project.owner.id)
   end
 
   # Runs code after a new commit has been pushed.
diff --git a/app/models/repository_language.rb b/app/models/repository_language.rb
new file mode 100644
index 00000000000..f467d4eafa3
--- /dev/null
+++ b/app/models/repository_language.rb
@@ -0,0 +1,12 @@
+class RepositoryLanguage < ActiveRecord::Base
+  belongs_to :project
+  belongs_to :programming_language
+
+  default_scope { includes(:programming_language) }
+
+  validates :project, presence: true
+  validates :share, inclusion: { in: 0..100, message: "The share of a lanuage is between 0 and 100" }
+  validates :programming_language, uniqueness: { scope: :project_id }
+
+  delegate :name, :color, to: :programming_language
+end
diff --git a/app/services/git_push_service.rb b/app/services/git_push_service.rb
index e3640e38bfa..637c1df4ad9 100644
--- a/app/services/git_push_service.rb
+++ b/app/services/git_push_service.rb
@@ -85,6 +85,8 @@ class GitPushService < BaseService
 
         types = Gitlab::FileDetector.types_in_paths(paths.to_a)
       end
+
+      DetectRepositoryLanguagesWorker.perform_async(@project.id, current_user.id)
     else
       types = []
     end
diff --git a/app/services/projects/detect_repository_languages_service.rb b/app/services/projects/detect_repository_languages_service.rb
new file mode 100644
index 00000000000..6669830ac8c
--- /dev/null
+++ b/app/services/projects/detect_repository_languages_service.rb
@@ -0,0 +1,53 @@
+module Projects
+  class DetectRepositoryLanguagesService < BaseService
+    attr_reader :detected_repository_languages, :programming_languages
+
+    def execute
+      repository_languages = project.repository_languages
+      detection = Gitlab::LanguageDetection.new(repository, repository_languages)
+
+      matching_programming_languages = ensure_programming_languages(detection)
+
+      RepositoryLanguage.transaction do
+        project.repository_languages.where(programming_language_id: detection.deletions).delete_all
+
+        detection.updates.each do |update|
+          RepositoryLanguage
+            .arel_table.update_manager
+            .where(project_id: project.id)
+            .where(programming_language_id: update[:programming_language_id])
+            .set(share: update[:share])
+        end
+
+        Gitlab::Database.bulk_insert(
+          RepositoryLanguage.table_name,
+          detection.insertions(matching_programming_languages)
+        )
+      end
+
+      project.repository_languages.reload
+    end
+
+    private
+
+    def ensure_programming_languages(detection)
+      existing_languages = ProgrammingLanguage.where(name: detection.languages)
+      return existing_languages if detection.languages.size == existing_languages.size
+
+      missing_languages = detection.languages - existing_languages.map(&:name)
+      created_languages = missing_languages.map do |name|
+        create_language(name, detection.language_color(name))
+      end
+
+      existing_languages + created_languages
+    end
+
+    def create_language(name, color)
+      ProgrammingLanguage.transaction do
+        ProgrammingLanguage.where(name: name).first_or_create(color: color)
+      end
+    rescue ActiveRecord::RecordNotUnique
+      retry
+    end
+  end
+end
diff --git a/app/views/projects/show.html.haml b/app/views/projects/show.html.haml
index 803ecca48f7..e011851be78 100644
--- a/app/views/projects/show.html.haml
+++ b/app/views/projects/show.html.haml
@@ -18,10 +18,11 @@
 = render "home_panel"
 
 - if can?(current_user, :download_code, @project)
-  %nav.project-stats{ class: container_class }
+  %nav.project-stats{ class: [container_class, ("limit-container-width" unless fluid_layout)] }
     = render 'stat_anchor_list', anchors: @project.statistics_anchors(show_auto_devops_callout: show_auto_devops_callout)
     = render 'stat_anchor_list', anchors: @project.statistics_buttons(show_auto_devops_callout: show_auto_devops_callout)
-
+    - if Feature.enabled?(:repository_languages, @project.namespace.becomes(Namespace))
+      = repository_languages_bar(@project.repository_languages)
 
 %div{ class: [container_class, ("limit-container-width" unless fluid_layout)] }
   - if @project.archived?
diff --git a/app/workers/all_queues.yml b/app/workers/all_queues.yml
index f2651cb54ec..e8b9999f83b 100644
--- a/app/workers/all_queues.yml
+++ b/app/workers/all_queues.yml
@@ -123,3 +123,4 @@
 - repository_update_remote_mirror
 - create_note_diff_file
 - delete_diff_files
+- detect_repository_languages
diff --git a/app/workers/detect_repository_languages_worker.rb b/app/workers/detect_repository_languages_worker.rb
new file mode 100644
index 00000000000..537b8fd5963
--- /dev/null
+++ b/app/workers/detect_repository_languages_worker.rb
@@ -0,0 +1,33 @@
+class DetectRepositoryLanguagesWorker
+  include ApplicationWorker
+  include ExceptionBacktrace
+  include ExclusiveLeaseGuard
+
+  sidekiq_options retry: 1
+
+  LEASE_TIMEOUT = 300
+
+  attr_reader :project
+
+  def perform(project_id, user_id)
+    @project = Project.find_by(id: project_id)
+    user = User.find_by(id: user_id)
+    return unless project && user
+
+    return if Feature.disabled?(:repository_languages, project.namespace)
+
+    try_obtain_lease do
+      ::Projects::DetectRepositoryLanguagesService.new(project, user).execute
+    end
+  end
+
+  private
+
+  def lease_timeout
+    LEASE_TIMEOUT
+  end
+
+  def lease_key
+    "gitlab:detect_repository_languages:#{project.id}"
+  end
+end
diff --git a/changelogs/unreleased/zj-repository-languages.yml b/changelogs/unreleased/zj-repository-languages.yml
new file mode 100644
index 00000000000..c42ba60be29
--- /dev/null
+++ b/changelogs/unreleased/zj-repository-languages.yml
@@ -0,0 +1,5 @@
+---
+title: Show repository languages for projects
+merge_request: 19480
+author:
+type: added
diff --git a/config/sidekiq_queues.yml b/config/sidekiq_queues.yml
index 3c85cd07d46..fb7738a5536 100644
--- a/config/sidekiq_queues.yml
+++ b/config/sidekiq_queues.yml
@@ -77,3 +77,4 @@
   - [repository_remove_remote, 1]
   - [create_note_diff_file, 1]
   - [delete_diff_files, 1]
+  - [detect_repository_languages, 1]
diff --git a/db/migrate/20180531185349_add_repository_languages.rb b/db/migrate/20180531185349_add_repository_languages.rb
new file mode 100644
index 00000000000..bfcfb618c87
--- /dev/null
+++ b/db/migrate/20180531185349_add_repository_languages.rb
@@ -0,0 +1,28 @@
+class AddRepositoryLanguages < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    create_table(:programming_languages) do |t|
+      t.string :name, null: false
+      t.string :color, null: false
+      t.datetime_with_timezone :created_at, null: false
+    end
+
+    create_table(:repository_languages, id: false) do |t|
+      t.references :project, null: false, foreign_key: { on_delete: :cascade }
+      t.references :programming_language, null: false
+      t.float :share, null: false
+    end
+
+    add_index :programming_languages, :name, unique: true
+    add_index :repository_languages, [:project_id, :programming_language_id],
+      unique: true, name: "index_repository_languages_on_project_and_languages_id"
+  end
+
+  def down
+    drop_table :repository_languages
+    drop_table :programming_languages
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 6f3433c1003..769baa825a5 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -1502,6 +1502,14 @@ ActiveRecord::Schema.define(version: 20180726172057) do
   add_index "personal_access_tokens", ["token"], name: "index_personal_access_tokens_on_token", unique: true, using: :btree
   add_index "personal_access_tokens", ["user_id"], name: "index_personal_access_tokens_on_user_id", using: :btree
 
+  create_table "programming_languages", force: :cascade do |t|
+    t.string "name", null: false
+    t.string "color", null: false
+    t.datetime_with_timezone "created_at", null: false
+  end
+
+  add_index "programming_languages", ["name"], name: "index_programming_languages_on_name", unique: true, using: :btree
+
   create_table "project_authorizations", id: false, force: :cascade do |t|
     t.integer "user_id", null: false
     t.integer "project_id", null: false
@@ -1788,6 +1796,14 @@ ActiveRecord::Schema.define(version: 20180726172057) do
   add_index "remote_mirrors", ["last_successful_update_at"], name: "index_remote_mirrors_on_last_successful_update_at", using: :btree
   add_index "remote_mirrors", ["project_id"], name: "index_remote_mirrors_on_project_id", using: :btree
 
+  create_table "repository_languages", id: false, force: :cascade do |t|
+    t.integer "project_id", null: false
+    t.integer "programming_language_id", null: false
+    t.float "share", null: false
+  end
+
+  add_index "repository_languages", ["project_id", "programming_language_id"], name: "index_repository_languages_on_project_and_languages_id", unique: true, using: :btree
+
   create_table "resource_label_events", id: :bigserial, force: :cascade do |t|
     t.integer "action", null: false
     t.integer "issue_id"
@@ -2359,6 +2375,7 @@ ActiveRecord::Schema.define(version: 20180726172057) do
   add_foreign_key "push_event_payloads", "events", name: "fk_36c74129da", on_delete: :cascade
   add_foreign_key "releases", "projects", name: "fk_47fe2a0596", on_delete: :cascade
   add_foreign_key "remote_mirrors", "projects", on_delete: :cascade
+  add_foreign_key "repository_languages", "projects", on_delete: :cascade
   add_foreign_key "resource_label_events", "issues", on_delete: :cascade
   add_foreign_key "resource_label_events", "labels", on_delete: :nullify
   add_foreign_key "resource_label_events", "merge_requests", on_delete: :cascade
diff --git a/lib/feature.rb b/lib/feature.rb
index d27b2b0e72f..09c5ef3ad94 100644
--- a/lib/feature.rb
+++ b/lib/feature.rb
@@ -46,6 +46,10 @@ class Feature
       get(key).enabled?(thing)
     end
 
+    def disabled?(key, thing = nil)
+      !enabled?(key, thing)
+    end
+
     def enable(key, thing = true)
       get(key).enable(thing)
     end
diff --git a/lib/gitlab/import_export/import_export.yml b/lib/gitlab/import_export/import_export.yml
index da3667faf7a..f69f98a78a3 100644
--- a/lib/gitlab/import_export/import_export.yml
+++ b/lib/gitlab/import_export/import_export.yml
@@ -107,6 +107,7 @@ excluded_attributes:
     - :storage_version
     - :remote_mirror_available_overridden
     - :description_html
+    - :repository_languages
   snippets:
     - :expired_at
   merge_request_diff:
diff --git a/lib/gitlab/language_detection.rb b/lib/gitlab/language_detection.rb
new file mode 100644
index 00000000000..a41435fdb79
--- /dev/null
+++ b/lib/gitlab/language_detection.rb
@@ -0,0 +1,68 @@
+module Gitlab
+  class LanguageDetection
+    MAX_LANGUAGES = 5
+
+    def initialize(repository, repository_languages)
+      @repository = repository
+      @repository_languages = repository_languages
+    end
+
+    def languages
+      detection.keys
+    end
+
+    def language_color(name)
+      detection.dig(name, :color)
+    end
+
+    # Newly detected languages, returned in a structure accepted by
+    # Gitlab::Database.bulk_insert
+    def insertions(programming_languages)
+      lang_to_id = programming_languages.map { |p| [p.name, p.id] }.to_h
+
+      (languages - previous_language_names).map do |new_lang|
+        {
+          project_id: @repository.project.id,
+          share: detection[new_lang][:value],
+          programming_language_id: lang_to_id[new_lang]
+        }
+      end
+    end
+
+    # updates analyses which records only require updating of their share
+    def updates
+      to_update = @repository_languages.select do |lang|
+        detection.key?(lang.name) && detection[lang.name][:value] != lang.share
+      end
+
+      to_update.map do |lang|
+        { programming_language_id: lang.programming_language_id, share: detection[lang.name][:value] }
+      end
+    end
+
+    # Returns the ids of the programming languages that do not occur in the detection
+    # as current repository languages
+    def deletions
+      @repository_languages.map do |repo_lang|
+        next if detection.key?(repo_lang.name)
+
+        repo_lang.programming_language_id
+      end.compact
+    end
+
+    private
+
+    def previous_language_names
+      @previous_language_names ||= @repository_languages.map(&:name)
+    end
+
+    def detection
+      @detection ||=
+        @repository
+        .languages
+        .first(MAX_LANGUAGES)
+        .map { |l| [l[:label], l] }
+        .to_h
+    end
+  end
+end
diff --git a/spec/factories/programming_languages.rb b/spec/factories/programming_languages.rb
new file mode 100644
index 00000000000..d3511d42b6c
--- /dev/null
+++ b/spec/factories/programming_languages.rb
@@ -0,0 +1,6 @@
+FactoryBot.define do
+  factory :programming_language do
+    name 'Ruby'
+    color '#123456'
+  end
+end
diff --git a/spec/factories/repository_languages.rb b/spec/factories/repository_languages.rb
new file mode 100644
index 00000000000..1757ba6766c
--- /dev/null
+++ b/spec/factories/repository_languages.rb
@@ -0,0 +1,7 @@
+FactoryBot.define do
+  factory :repository_language do
+    project
+    programming_language
+    share 98.5
+  end
+end
diff --git a/spec/lib/gitlab/import_export/all_models.yml b/spec/lib/gitlab/import_export/all_models.yml
index c175dc1e4dd..b3e3ead9c5e 100644
--- a/spec/lib/gitlab/import_export/all_models.yml
+++ b/spec/lib/gitlab/import_export/all_models.yml
@@ -297,6 +297,7 @@ project:
 - settings
 - ci_cd_settings
 - import_export_upload
+- repository_languages
 award_emoji:
 - awardable
 - user
diff --git a/spec/lib/gitlab/language_detection_spec.rb b/spec/lib/gitlab/language_detection_spec.rb
new file mode 100644
index 00000000000..9636fbd401b
--- /dev/null
+++ b/spec/lib/gitlab/language_detection_spec.rb
@@ -0,0 +1,85 @@
+require 'spec_helper'
+
+describe Gitlab::LanguageDetection do
+  set(:project) { create(:project, :repository) }
+  set(:ruby) { create(:programming_language, name: 'Ruby') }
+  set(:haskell) { create(:programming_language, name: 'Haskell') }
+  let(:repository) { project.repository }
+  let(:detection) do
+    [{ value: 66.63, label: "Ruby", color: "#701516", highlight: "#701516" },
+     { value: 12.96, label: "JavaScript", color: "#f1e05a", highlight: "#f1e05a" },
+     { value: 7.9, label: "Elixir", color: "#e34c26", highlight: "#e34c26" },
+     { value: 2.51, label: "CoffeeScript", color: "#244776", highlight: "#244776" },
+     { value: 1.51, label: "Go", color: "#2a4776", highlight: "#244776" },
+     { value: 1.1, label: "MepmepLang", color: "#2a4776", highlight: "#244776" }]
+  end
+  let(:repository_languages) do
+    [RepositoryLanguage.new(share: 10, programming_language: ruby)]
+  end
+
+  subject { described_class.new(repository, repository_languages) }
+
+  before do
+    allow(repository).to receive(:languages).and_return(detection)
+  end
+
+  describe '#languages' do
+    it 'returns the language names' do
+      expect(subject.languages).to eq(%w[Ruby JavaScript Elixir CoffeeScript Go])
+    end
+  end
+
+  describe '#insertions' do
+    let(:programming_languages) { [ruby, haskell] }
+    let(:detection) do
+      [{ value: 10, label: haskell.name, color: haskell.color }]
+    end
+
+    it 'only includes new languages' do
+      insertions = subject.insertions(programming_languages)
+
+      expect(insertions).not_to be_empty
+      expect(insertions.first[:project_id]).to be(project.id)
+      expect(insertions.first[:programming_language_id]).to be(haskell.id)
+      expect(insertions.first[:share]).to be(10)
+    end
+  end
+
+  describe '#updates' do
+    it 'updates the share of languages' do
+      first_update = subject.updates.first
+
+      expect(first_update).not_to be_nil
+      expect(first_update[:programming_language_id]).to eq(ruby.id)
+      expect(first_update[:share]).to eq(66.63)
+    end
+
+    it 'does not include languages to be removed' do
+      ids = subject.updates.map { |h| h[:programming_language_id] }
+
+      expect(ids).not_to include(haskell.id)
+    end
+
+    context 'when silent writes occur' do
+      let(:repository_languages) do
+        [RepositoryLanguage.new(share: 66.63, programming_language: ruby)]
+      end
+
+      it "doesn't include them in the result" do
+        expect(subject.updates).to be_empty
+      end
+    end
+  end
+
+  describe '#deletions' do
+    let(:repository_languages) do
+      [RepositoryLanguage.new(share: 10, programming_language: ruby),
+       RepositoryLanguage.new(share: 5, programming_language: haskell)]
+    end
+
+    it 'lists undetected languages' do
+      expect(subject.deletions).not_to be_empty
+      expect(subject.deletions).to include(haskell.id)
+    end
+  end
+end
diff --git a/spec/models/programming_language_spec.rb b/spec/models/programming_language_spec.rb
new file mode 100644
index 00000000000..99cd358f863
--- /dev/null
+++ b/spec/models/programming_language_spec.rb
@@ -0,0 +1,11 @@
+require 'spec_helper'
+
+describe ProgrammingLanguage do
+  it { is_expected.to respond_to(:name) }
+  it { is_expected.to respond_to(:color) }
+
+  it { is_expected.to validate_presence_of(:name) }
+  it { is_expected.to allow_value("#000000").for(:color) }
+  it { is_expected.not_to allow_value("000000").for(:color) }
+  it { is_expected.not_to allow_value("#0z0000").for(:color) }
+end
diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index ef4167a3912..340d2d95500 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -69,6 +69,7 @@ describe Project do
     it { is_expected.to have_many(:pages_domains) }
     it { is_expected.to have_many(:labels).class_name('ProjectLabel') }
     it { is_expected.to have_many(:users_star_projects) }
+    it { is_expected.to have_many(:repository_languages) }
     it { is_expected.to have_many(:environments) }
     it { is_expected.to have_many(:deployments) }
     it { is_expected.to have_many(:todos) }
diff --git a/spec/models/repository_language_spec.rb b/spec/models/repository_language_spec.rb
new file mode 100644
index 00000000000..e2e4beb512f
--- /dev/null
+++ b/spec/models/repository_language_spec.rb
@@ -0,0 +1,16 @@
+require 'spec_helper'
+
+describe RepositoryLanguage do
+  let(:repository_language) { build(:repository_language) }
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:project) }
+    it { is_expected.to belong_to(:programming_language) }
+  end
+
+  describe 'validations' do
+    it { is_expected.to allow_value(0).for(:share) }
+    it { is_expected.to allow_value(100.0).for(:share) }
+    it { is_expected.not_to allow_value(100.1).for(:share) }
+  end
+end
diff --git a/spec/services/git_push_service_spec.rb b/spec/services/git_push_service_spec.rb
index 657afb2b2b5..a3c9a660c2f 100644
--- a/spec/services/git_push_service_spec.rb
+++ b/spec/services/git_push_service_spec.rb
@@ -3,8 +3,8 @@ require 'spec_helper'
 describe GitPushService, services: true do
   include RepoHelpers
 
-  let(:user)     { create(:user) }
-  let(:project)  { create(:project, :repository) }
+  set(:user)     { create(:user) }
+  set(:project)  { create(:project, :repository) }
   let(:blankrev) { Gitlab::Git::BLANK_SHA }
   let(:oldrev)   { sample_commit.parent_id }
   let(:newrev)   { sample_commit.id }
diff --git a/spec/services/projects/detect_repository_languages_service_spec.rb b/spec/services/projects/detect_repository_languages_service_spec.rb
new file mode 100644
index 00000000000..f90d558938f
--- /dev/null
+++ b/spec/services/projects/detect_repository_languages_service_spec.rb
@@ -0,0 +1,54 @@
+require 'spec_helper'
+
+describe Projects::DetectRepositoryLanguagesService, :clean_gitlab_redis_shared_state do
+  set(:project) { create(:project, :repository) }
+
+  subject { described_class.new(project, project.owner) }
+
+  before do
+    allow(Feature).to receive(:disabled?).and_return(false)
+  end
+
+  describe '#execute' do
+    context 'without previous detection' do
+      it 'inserts new programming languages in the database' do
+        subject.execute
+
+        expect(ProgrammingLanguage.exists?(name: 'Ruby')).to be(true)
+        expect(ProgrammingLanguage.count).to be(4)
+      end
+
+      it 'inserts the repository langauges' do
+        names = subject.execute.map(&:name)
+
+        expect(names).to eq(%w[Ruby JavaScript HTML CoffeeScript])
+      end
+    end
+
+    context 'with a previous detection' do
+      before do
+        subject.execute
+
+        allow(project.repository).to receive(:languages).and_return(
+          [{ value: 99.63, label: "Ruby", color: "#701516", highlight: "#701516" },
+           { value: 0.3, label: "D", color: "#701516", highlight: "#701516" }]
+        )
+      end
+
+      it 'updates the repository languages' do
+        repository_languages = subject.execute.map(&:name)
+
+        expect(repository_languages).to eq(%w[Ruby D])
+      end
+    end
+
+    context 'when no repository exists' do
+      set(:project) { create(:project) }
+
+      it 'has no languages' do
+        expect(subject.execute).to be_empty
+        expect(project.repository_languages).to be_empty
+      end
+    end
+  end
+end
diff --git a/spec/workers/detect_repository_languages_worker_spec.rb b/spec/workers/detect_repository_languages_worker_spec.rb
new file mode 100644
index 00000000000..ff3878fbc8e
--- /dev/null
+++ b/spec/workers/detect_repository_languages_worker_spec.rb
@@ -0,0 +1,32 @@
+require 'spec_helper'
+
+describe DetectRepositoryLanguagesWorker do
+  set(:project) { create(:project) }
+  let(:user) { project.owner }
+
+  subject { described_class.new }
+
+  describe '#perform' do
+    it 'calls de DetectRepositoryLanguages service' do
+      service = double
+      allow(::Projects::DetectRepositoryLanguagesService).to receive(:new).and_return(service)
+      expect(service).to receive(:execute)
+
+      subject.perform(project.id, user.id)
+    end
+
+    context 'when invalid ids are used' do
+      it 'does not raise when the project could not be found' do
+        expect do
+          subject.perform(-1, user.id)
+        end.not_to raise_error
+      end
+
+      it 'does not raise when the user could not be found' do
+        expect do
+          subject.perform(project.id, -1)
+        end.not_to raise_error
+      end
+    end
+  end
+end