Merge branch 'master' into add-canary-favicon

64 files changed, 801 insertions, 183 deletions

diff --git a/app/serializers/analytics_build_entity.rb b/app/serializers/analytics_build_entity.rb
index ad7ad020b03..bdc22d71202 100644
--- a/app/serializers/analytics_build_entity.rb
+++ b/app/serializers/analytics_build_entity.rb
@@ -35,6 +35,6 @@ class AnalyticsBuildEntity < Grape::Entity
   private
 
   def url_to(route, build, id = nil)
-    public_send("#{route}_url", build.project.namespace, build.project, id || build)
+    public_send("#{route}_url", build.project.namespace, build.project, id || build) # rubocop:disable GitlabSecurity/PublicSend
   end
 end
diff --git a/app/serializers/analytics_issue_entity.rb b/app/serializers/analytics_issue_entity.rb
index 44c50f18613..b7d95ea020f 100644
--- a/app/serializers/analytics_issue_entity.rb
+++ b/app/serializers/analytics_issue_entity.rb
@@ -24,6 +24,6 @@ class AnalyticsIssueEntity < Grape::Entity
   private
 
   def url_to(route, id)
-    public_send("#{route}_url", request.project.namespace, request.project, id)
+    public_send("#{route}_url", request.project.namespace, request.project, id) # rubocop:disable GitlabSecurity/PublicSend
   end
 end
diff --git a/app/serializers/analytics_stage_entity.rb b/app/serializers/analytics_stage_entity.rb
index 564612202b5..3e355a13e06 100644
--- a/app/serializers/analytics_stage_entity.rb
+++ b/app/serializers/analytics_stage_entity.rb
@@ -7,6 +7,7 @@ class AnalyticsStageEntity < Grape::Entity
   expose :description
 
   expose :median, as: :value do |stage|
-    stage.median && !stage.median.zero? ? distance_of_time_in_words(stage.median) : nil
+    # median returns a BatchLoader instance which we first have to unwrap by using to_i
+    !stage.median.to_i.zero? ? distance_of_time_in_words(stage.median) : nil
   end
 end
diff --git a/app/serializers/award_emoji_entity.rb b/app/serializers/award_emoji_entity.rb
new file mode 100644
index 00000000000..6e03cd02392
--- /dev/null
+++ b/app/serializers/award_emoji_entity.rb
@@ -0,0 +1,4 @@
+class AwardEmojiEntity < Grape::Entity
+  expose :name
+  expose :user, using: API::Entities::UserSafe
+end
diff --git a/app/serializers/base_serializer.rb b/app/serializers/base_serializer.rb
index 4e6c15f673b..8cade280b0c 100644
--- a/app/serializers/base_serializer.rb
+++ b/app/serializers/base_serializer.rb
@@ -1,6 +1,9 @@
 class BaseSerializer
-  def initialize(parameters = {})
-    @request = EntityRequest.new(parameters)
+  attr_reader :params
+
+  def initialize(params = {})
+    @params = params
+    @request = EntityRequest.new(params)
   end
 
   def represent(resource, opts = {}, entity_class = nil)
diff --git a/app/serializers/blob_entity.rb b/app/serializers/blob_entity.rb
new file mode 100644
index 00000000000..ad039a2623d
--- /dev/null
+++ b/app/serializers/blob_entity.rb
@@ -0,0 +1,13 @@
+class BlobEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :id, :path, :name, :mode
+
+  expose :icon do |blob|
+    IconsHelper.file_type_icon_class('file', blob.mode, blob.name)
+  end
+
+  expose :url do |blob|
+    project_blob_path(request.project, File.join(request.ref, blob.path))
+  end
+end
diff --git a/app/serializers/build_action_entity.rb b/app/serializers/build_action_entity.rb
index 301b718d060..f2d76a8ad81 100644
--- a/app/serializers/build_action_entity.rb
+++ b/app/serializers/build_action_entity.rb
@@ -6,10 +6,7 @@ class BuildActionEntity < Grape::Entity
   end
 
   expose :path do |build|
-    play_namespace_project_job_path(
-      build.project.namespace,
-      build.project,
-      build)
+    play_project_job_path(build.project, build)
   end
 
   expose :playable?, as: :playable
diff --git a/app/serializers/build_artifact_entity.rb b/app/serializers/build_artifact_entity.rb
index cb55c98f7c6..6e0e33bc09b 100644
--- a/app/serializers/build_artifact_entity.rb
+++ b/app/serializers/build_artifact_entity.rb
@@ -9,24 +9,15 @@ class BuildArtifactEntity < Grape::Entity
   expose :artifacts_expire_at, as: :expire_at
 
   expose :path do |job|
-    download_namespace_project_job_artifacts_path(
-      project.namespace,
-      project,
-      job)
+    download_project_job_artifacts_path(project, job)
   end
 
   expose :keep_path, if: -> (*) { job.has_expiring_artifacts? } do |job|
-    keep_namespace_project_job_artifacts_path(
-      project.namespace,
-      project,
-      job)
+    keep_project_job_artifacts_path(project, job)
   end
 
   expose :browse_path do |job|
-    browse_namespace_project_job_artifacts_path(
-      project.namespace,
-      project,
-      job)
+    browse_project_job_artifacts_path(project, job)
   end
 
   private
diff --git a/app/serializers/build_details_entity.rb b/app/serializers/build_details_entity.rb
index eeb5399aa8b..69d46f5ec14 100644
--- a/app/serializers/build_details_entity.rb
+++ b/app/serializers/build_details_entity.rb
@@ -6,8 +6,8 @@ class BuildDetailsEntity < JobEntity
   expose :pipeline, using: PipelineEntity
 
   expose :erased_by, if: -> (*) { build.erased? }, using: UserEntity
-  expose :erase_path, if: -> (*) { build.erasable? && can?(current_user, :update_build, project) } do |build|
-    erase_namespace_project_job_path(project.namespace, project, build)
+  expose :erase_path, if: -> (*) { build.erasable? && can?(current_user, :erase_build, build) } do |build|
+    erase_project_job_path(project, build)
   end
 
   expose :merge_request, if: -> (*) { can?(current_user, :read_merge_request, build.merge_request) } do
@@ -16,23 +16,24 @@ class BuildDetailsEntity < JobEntity
     end
 
     expose :path do |build|
-      namespace_project_merge_request_path(project.namespace, project, build.merge_request)
+      project_merge_request_path(build.merge_request.project,
+                                 build.merge_request)
     end
   end
 
   expose :new_issue_path, if: -> (*) { can?(request.current_user, :create_issue, project) && build.failed? } do |build|
-    new_namespace_project_issue_path(project.namespace, project, issue: build_failed_issue_options)
+    new_project_issue_path(project, issue: build_failed_issue_options)
   end
 
   expose :raw_path do |build|
-    raw_namespace_project_job_path(project.namespace, project, build)
+    raw_project_job_path(project, build)
   end
 
   private
 
   def build_failed_issue_options
-    { title: "Build Failed ##{build.id}",
-      description: namespace_project_job_path(project.namespace, project, build) }
+    { title: "Job Failed ##{build.id}",
+      description: "Job [##{build.id}](#{project_job_path(project, build)}) failed for #{build.sha}:\n" }
   end
 
   def current_user
diff --git a/app/serializers/cluster_application_entity.rb b/app/serializers/cluster_application_entity.rb
new file mode 100644
index 00000000000..b22a0b666ef
--- /dev/null
+++ b/app/serializers/cluster_application_entity.rb
@@ -0,0 +1,6 @@
+class ClusterApplicationEntity < Grape::Entity
+  expose :name
+  expose :status_name, as: :status
+  expose :status_reason
+  expose :external_ip, if: -> (e, _) { e.respond_to?(:external_ip) }
+end
diff --git a/app/serializers/cluster_entity.rb b/app/serializers/cluster_entity.rb
new file mode 100644
index 00000000000..7e5b0997878
--- /dev/null
+++ b/app/serializers/cluster_entity.rb
@@ -0,0 +1,7 @@
+class ClusterEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :status_name, as: :status
+  expose :status_reason
+  expose :applications, using: ClusterApplicationEntity
+end
diff --git a/app/serializers/cluster_serializer.rb b/app/serializers/cluster_serializer.rb
new file mode 100644
index 00000000000..2e13c1501e7
--- /dev/null
+++ b/app/serializers/cluster_serializer.rb
@@ -0,0 +1,7 @@
+class ClusterSerializer < BaseSerializer
+  entity ClusterEntity
+
+  def represent_status(resource)
+    represent(resource, { only: [:status, :status_reason, :applications] })
+  end
+end
diff --git a/app/serializers/commit_entity.rb b/app/serializers/commit_entity.rb
index 31763955f97..c8dd98cc04d 100644
--- a/app/serializers/commit_entity.rb
+++ b/app/serializers/commit_entity.rb
@@ -1,4 +1,4 @@
-class CommitEntity < API::Entities::RepoCommit
+class CommitEntity < API::Entities::Commit
   include RequestAwareEntity
 
   expose :author, using: UserEntity
@@ -8,16 +8,10 @@ class CommitEntity < API::Entities::RepoCommit
   end
 
   expose :commit_url do |commit|
-    namespace_project_commit_url(
-      request.project.namespace,
-      request.project,
-      commit)
+    project_commit_url(request.project, commit)
   end
 
   expose :commit_path do |commit|
-    namespace_project_commit_path(
-      request.project.namespace,
-      request.project,
-      commit)
+    project_commit_path(request.project, commit)
   end
 end
diff --git a/app/serializers/concerns/with_pagination.rb b/app/serializers/concerns/with_pagination.rb
new file mode 100644
index 00000000000..89631b73fcf
--- /dev/null
+++ b/app/serializers/concerns/with_pagination.rb
@@ -0,0 +1,22 @@
+module WithPagination
+  attr_accessor :paginator
+
+  def with_pagination(request, response)
+    tap { self.paginator = Gitlab::Serializer::Pagination.new(request, response) }
+  end
+
+  def paginated?
+    paginator.present?
+  end
+
+  # super is `BaseSerializer#represent` here.
+  #
+  # we shouldn't try to paginate single resources
+  def represent(resource, opts = {})
+    if paginated? && resource.respond_to?(:page)
+      super(paginator.paginate(resource), opts)
+    else
+      super(resource, opts)
+    end
+  end
+end
diff --git a/app/serializers/container_repositories_serializer.rb b/app/serializers/container_repositories_serializer.rb
new file mode 100644
index 00000000000..56dc70b5687
--- /dev/null
+++ b/app/serializers/container_repositories_serializer.rb
@@ -0,0 +1,3 @@
+class ContainerRepositoriesSerializer < BaseSerializer
+  entity ContainerRepositoryEntity
+end
diff --git a/app/serializers/container_repository_entity.rb b/app/serializers/container_repository_entity.rb
new file mode 100644
index 00000000000..1103cf30a07
--- /dev/null
+++ b/app/serializers/container_repository_entity.rb
@@ -0,0 +1,25 @@
+class ContainerRepositoryEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :id, :path, :location
+
+  expose :tags_path do |repository|
+    project_registry_repository_tags_path(project, repository, format: :json)
+  end
+
+  expose :destroy_path, if: -> (*) { can_destroy? } do |repository|
+    project_container_registry_path(project, repository, format: :json)
+  end
+
+  private
+
+  alias_method :repository, :object
+
+  def project
+    request.project
+  end
+
+  def can_destroy?
+    can?(request.current_user, :update_container_image, project)
+  end
+end
diff --git a/app/serializers/container_tag_entity.rb b/app/serializers/container_tag_entity.rb
new file mode 100644
index 00000000000..8f1488e6cbb
--- /dev/null
+++ b/app/serializers/container_tag_entity.rb
@@ -0,0 +1,23 @@
+class ContainerTagEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :name, :location, :revision, :short_revision, :total_size, :created_at
+
+  expose :destroy_path, if: -> (*) { can_destroy? } do |tag|
+    project_registry_repository_tag_path(project, tag.repository, tag.name)
+  end
+
+  private
+
+  alias_method :tag, :object
+
+  def project
+    request.project
+  end
+
+  def can_destroy?
+    # TODO: We check permission against @project, not tag,
+    # as tag is no AR object that is attached to project
+    can?(request.current_user, :update_container_image, project)
+  end
+end
diff --git a/app/serializers/container_tags_serializer.rb b/app/serializers/container_tags_serializer.rb
new file mode 100644
index 00000000000..6ff3adff135
--- /dev/null
+++ b/app/serializers/container_tags_serializer.rb
@@ -0,0 +1,17 @@
+class ContainerTagsSerializer < BaseSerializer
+  entity ContainerTagEntity
+
+  def with_pagination(request, response)
+    tap { @paginator = Gitlab::Serializer::Pagination.new(request, response) }
+  end
+
+  def paginated?
+    @paginator.present?
+  end
+
+  def represent(resource, opts = {})
+    resource = @paginator.paginate(resource) if paginated?
+
+    super(resource, opts)
+  end
+end
diff --git a/app/serializers/deploy_key_entity.rb b/app/serializers/deploy_key_entity.rb
index 068013c8829..2678f99510c 100644
--- a/app/serializers/deploy_key_entity.rb
+++ b/app/serializers/deploy_key_entity.rb
@@ -3,19 +3,20 @@ class DeployKeyEntity < Grape::Entity
   expose :user_id
   expose :title
   expose :fingerprint
-  expose :can_push
   expose :destroyed_when_orphaned?, as: :destroyed_when_orphaned
   expose :almost_orphaned?, as: :almost_orphaned
   expose :created_at
   expose :updated_at
-  expose :projects, using: ProjectEntity do |deploy_key|
-    deploy_key.projects.select { |project| options[:user].can?(:read_project, project) }
+  expose :deploy_keys_projects, using: DeployKeysProjectEntity do |deploy_key|
+    deploy_key.deploy_keys_projects
+              .without_project_deleted
+              .select { |deploy_key_project| Ability.allowed?(options[:user], :read_project, deploy_key_project.project) }
   end
   expose :can_edit
 
   private
 
   def can_edit
-    options[:user].can?(:update_deploy_key, object)
+    Ability.allowed?(options[:user], :update_deploy_key, object)
   end
 end
diff --git a/app/serializers/deploy_keys_project_entity.rb b/app/serializers/deploy_keys_project_entity.rb
new file mode 100644
index 00000000000..568ef5ab75e
--- /dev/null
+++ b/app/serializers/deploy_keys_project_entity.rb
@@ -0,0 +1,4 @@
+class DeployKeysProjectEntity < Grape::Entity
+  expose :can_push
+  expose :project, using: ProjectEntity
+end
diff --git a/app/serializers/deployment_entity.rb b/app/serializers/deployment_entity.rb
index e493c9162fd..241c689bccd 100644
--- a/app/serializers/deployment_entity.rb
+++ b/app/serializers/deployment_entity.rb
@@ -11,10 +11,7 @@ class DeploymentEntity < Grape::Entity
     end
 
     expose :ref_path do |deployment|
-      namespace_project_tree_path(
-        deployment.project.namespace,
-        deployment.project,
-        id: deployment.ref)
+      project_tree_path(deployment.project, id: deployment.ref)
     end
   end
 
diff --git a/app/serializers/diff_file_entity.rb b/app/serializers/diff_file_entity.rb
new file mode 100644
index 00000000000..6e68d275047
--- /dev/null
+++ b/app/serializers/diff_file_entity.rb
@@ -0,0 +1,41 @@
+class DiffFileEntity < Grape::Entity
+  include DiffHelper
+  include SubmoduleHelper
+  include BlobHelper
+  include IconsHelper
+  include ActionView::Helpers::TagHelper
+
+  expose :submodule?, as: :submodule
+
+  expose :submodule_link do |diff_file|
+    submodule_links(diff_file.blob, diff_file.content_sha, diff_file.repository).first
+  end
+
+  expose :blob_path do |diff_file|
+    diff_file.blob.path
+  end
+
+  expose :blob_icon do |diff_file|
+    blob_icon(diff_file.b_mode, diff_file.file_path)
+  end
+
+  expose :file_path
+  expose :deleted_file?, as: :deleted_file
+  expose :renamed_file?, as: :renamed_file
+  expose :old_path
+  expose :new_path
+  expose :mode_changed?, as: :mode_changed
+  expose :a_mode
+  expose :b_mode
+  expose :text?, as: :text
+
+  expose :old_path_html do |diff_file|
+    old_path = mark_inline_diffs(diff_file.old_path, diff_file.new_path)
+    old_path
+  end
+
+  expose :new_path_html do |diff_file|
+    _, new_path = mark_inline_diffs(diff_file.old_path, diff_file.new_path)
+    new_path
+  end
+end
diff --git a/app/serializers/discussion_entity.rb b/app/serializers/discussion_entity.rb
new file mode 100644
index 00000000000..bbbcf6a97c1
--- /dev/null
+++ b/app/serializers/discussion_entity.rb
@@ -0,0 +1,48 @@
+class DiscussionEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :id, :reply_id
+  expose :expanded?, as: :expanded
+
+  expose :notes, using: NoteEntity
+
+  expose :individual_note?, as: :individual_note
+  expose :resolvable?, as: :resolvable
+  expose :resolved?, as: :resolved
+  expose :resolve_path, if: -> (d, _) { d.resolvable? } do |discussion|
+    resolve_project_merge_request_discussion_path(discussion.project, discussion.noteable, discussion.id)
+  end
+  expose :resolve_with_issue_path do |discussion|
+    new_project_issue_path(discussion.project, merge_request_to_resolve_discussions_of: discussion.noteable.iid, discussion_to_resolve: discussion.id)
+  end
+
+  expose :diff_file, using: DiffFileEntity, if: -> (d, _) { defined? d.diff_file }
+
+  expose :diff_discussion?, as: :diff_discussion
+
+  expose :truncated_diff_lines, if: -> (d, _) { (defined? d.diff_file) && d.diff_file.text? } do |discussion|
+    options[:context].render_to_string(
+      partial: "projects/diffs/line",
+      collection: discussion.truncated_diff_lines,
+      as: :line,
+      locals: { diff_file: discussion.diff_file,
+                discussion_expanded: true,
+                plain: true },
+      layout: false,
+      formats: [:html]
+    )
+  end
+
+  expose :image_diff_html, if: -> (d, _) { defined? d.diff_file } do |discussion|
+    diff_file = discussion.diff_file
+    partial = diff_file.new_file? || diff_file.deleted_file? ? 'single_image_diff' : 'replaced_image_diff'
+    options[:context].render_to_string(
+      partial: "projects/diffs/#{partial}",
+      locals: { diff_file: diff_file,
+                position: discussion.position.to_json,
+                click_to_comment: false },
+      layout: false,
+      formats: [:html]
+    )
+  end
+end
diff --git a/app/serializers/discussion_serializer.rb b/app/serializers/discussion_serializer.rb
new file mode 100644
index 00000000000..ed5e1224bb2
--- /dev/null
+++ b/app/serializers/discussion_serializer.rb
@@ -0,0 +1,3 @@
+class DiscussionSerializer < BaseSerializer
+  entity DiscussionEntity
+end
diff --git a/app/serializers/environment_entity.rb b/app/serializers/environment_entity.rb
index 4e8a3c67b21..ba0ae6ba8a0 100644
--- a/app/serializers/environment_entity.rb
+++ b/app/serializers/environment_entity.rb
@@ -10,32 +10,24 @@ class EnvironmentEntity < Grape::Entity
   expose :stop_action?
 
   expose :metrics_path, if: -> (environment, _) { environment.has_metrics? } do |environment|
-    metrics_namespace_project_environment_path(
-      environment.project.namespace,
-      environment.project,
-      environment)
+    metrics_project_environment_path(environment.project, environment)
   end
 
   expose :environment_path do |environment|
-    namespace_project_environment_path(
-      environment.project.namespace,
-      environment.project,
-      environment)
+    project_environment_path(environment.project, environment)
   end
 
   expose :stop_path do |environment|
-    stop_namespace_project_environment_path(
-      environment.project.namespace,
-      environment.project,
-      environment)
+    stop_project_environment_path(environment.project, environment)
   end
 
   expose :terminal_path, if: ->(environment, _) { environment.has_terminals? } do |environment|
     can?(request.current_user, :admin_environment, environment.project) &&
-      terminal_namespace_project_environment_path(
-        environment.project.namespace,
-        environment.project,
-        environment)
+      terminal_project_environment_path(environment.project, environment)
+  end
+
+  expose :folder_path do |environment|
+    folder_project_environments_path(environment.project, environment.folder_name)
   end
 
   expose :created_at, :updated_at
diff --git a/app/serializers/environment_serializer.rb b/app/serializers/environment_serializer.rb
index d0a60f134da..84722f33f59 100644
--- a/app/serializers/environment_serializer.rb
+++ b/app/serializers/environment_serializer.rb
@@ -1,4 +1,6 @@
 class EnvironmentSerializer < BaseSerializer
+  include WithPagination
+
   Item = Struct.new(:name, :size, :latest)
 
   entity EnvironmentEntity
@@ -7,18 +9,10 @@ class EnvironmentSerializer < BaseSerializer
     tap { @itemize = true }
   end
 
-  def with_pagination(request, response)
-    tap { @paginator = Gitlab::Serializer::Pagination.new(request, response) }
-  end
-
   def itemized?
     @itemize
   end
 
-  def paginated?
-    @paginator.present?
-  end
-
   def represent(resource, opts = {})
     if itemized?
       itemize(resource).map do |item|
@@ -27,8 +21,6 @@ class EnvironmentSerializer < BaseSerializer
           latest: super(item.latest, opts) }
       end
     else
-      resource = @paginator.paginate(resource) if paginated?
-
       super(resource, opts)
     end
   end
@@ -36,9 +28,9 @@ class EnvironmentSerializer < BaseSerializer
   private
 
   def itemize(resource)
-    items = resource.order('folder_name ASC')
+    items = resource.order('folder ASC')
       .group('COALESCE(environment_type, name)')
-      .select('COALESCE(environment_type, name) AS folder_name',
+      .select('COALESCE(environment_type, name) AS folder',
               'COUNT(*) AS size', 'MAX(id) AS last_id')
 
     # It makes a difference when you call `paginate` method, because
@@ -49,7 +41,7 @@ class EnvironmentSerializer < BaseSerializer
     environments = resource.where(id: items.map(&:last_id)).index_by(&:id)
 
     items.map do |item|
-      Item.new(item.folder_name, item.size, environments[item.last_id])
+      Item.new(item.folder, item.size, environments[item.last_id])
     end
   end
 end
diff --git a/app/serializers/event_entity.rb b/app/serializers/event_entity.rb
deleted file mode 100644
index 935d67a4f37..00000000000
--- a/app/serializers/event_entity.rb
+++ /dev/null
@@ -1,4 +0,0 @@
-class EventEntity < Grape::Entity
-  expose :author, using: UserEntity
-  expose :updated_at
-end
diff --git a/app/serializers/group_child_entity.rb b/app/serializers/group_child_entity.rb
new file mode 100644
index 00000000000..15ec0f89bb2
--- /dev/null
+++ b/app/serializers/group_child_entity.rb
@@ -0,0 +1,97 @@
+class GroupChildEntity < Grape::Entity
+  include ActionView::Helpers::NumberHelper
+  include RequestAwareEntity
+  include MarkupHelper
+
+  expose :id, :name, :description, :visibility, :full_name,
+         :created_at, :updated_at, :avatar_url
+
+  expose :type do |instance|
+    type
+  end
+
+  expose :can_edit do |instance|
+    can_edit?
+  end
+
+  expose :edit_path do |instance|
+    # We know `type` will be one either `project` or `group`.
+    # The `edit_polymorphic_path` helper would try to call the path helper
+    # with a plural: `edit_groups_path(instance)` or `edit_projects_path(instance)`
+    # while our methods are `edit_group_path` or `edit_group_path`
+    public_send("edit_#{type}_path", instance) # rubocop:disable GitlabSecurity/PublicSend
+  end
+
+  expose :relative_path do |instance|
+    polymorphic_path(instance)
+  end
+
+  expose :permission do |instance|
+    membership&.human_access
+  end
+
+  # Project only attributes
+  expose :star_count,
+         if: lambda { |_instance, _options| project? }
+
+  # Group only attributes
+  expose :children_count, :parent_id, :project_count, :subgroup_count,
+         unless: lambda { |_instance, _options| project? }
+
+  expose :leave_path, unless: lambda { |_instance, _options| project? } do |instance|
+    leave_group_members_path(instance)
+  end
+
+  expose :can_leave, unless: lambda { |_instance, _options| project? } do |instance|
+    if membership
+      can?(request.current_user, :destroy_group_member, membership)
+    else
+      false
+    end
+  end
+
+  expose :number_projects_with_delimiter, unless: lambda { |_instance, _options| project? } do |instance|
+    number_with_delimiter(instance.project_count)
+  end
+
+  expose :number_users_with_delimiter, unless: lambda { |_instance, _options| project? } do |instance|
+    number_with_delimiter(instance.member_count)
+  end
+
+  expose :markdown_description do |instance|
+    markdown_description
+  end
+
+  private
+
+  def membership
+    return unless request.current_user
+
+    @membership ||= request.current_user.members.find_by(source: object)
+  end
+
+  def project?
+    object.is_a?(Project)
+  end
+
+  def type
+    object.class.name.downcase
+  end
+
+  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
diff --git a/app/serializers/group_child_serializer.rb b/app/serializers/group_child_serializer.rb
new file mode 100644
index 00000000000..2baef0a5703
--- /dev/null
+++ b/app/serializers/group_child_serializer.rb
@@ -0,0 +1,51 @@
+class GroupChildSerializer < BaseSerializer
+  include WithPagination
+
+  attr_reader :hierarchy_root, :should_expand_hierarchy
+
+  entity GroupChildEntity
+
+  def expand_hierarchy(hierarchy_root = nil)
+    @hierarchy_root = hierarchy_root
+    @should_expand_hierarchy = true
+
+    self
+  end
+
+  def represent(resource, opts = {}, entity_class = nil)
+    if should_expand_hierarchy
+      paginator.paginate(resource) if paginated?
+      represent_hierarchies(resource, opts)
+    else
+      super(resource, opts)
+    end
+  end
+
+  protected
+
+  def represent_hierarchies(children, opts)
+    if children.is_a?(GroupDescendant)
+      represent_hierarchy(children.hierarchy(hierarchy_root), opts).first
+    else
+      hierarchies = GroupDescendant.build_hierarchy(children, hierarchy_root)
+      # When an array was passed, we always want to represent an array.
+      # Even if the hierarchy only contains one element
+      represent_hierarchy(Array.wrap(hierarchies), opts)
+    end
+  end
+
+  def represent_hierarchy(hierarchy, opts)
+    serializer = self.class.new(params)
+
+    if hierarchy.is_a?(Hash)
+      hierarchy.map do |parent, children|
+        serializer.represent(parent, opts)
+          .merge(children: Array.wrap(serializer.represent_hierarchy(children, opts)))
+      end
+    elsif hierarchy.is_a?(Array)
+      hierarchy.flat_map { |child| serializer.represent_hierarchy(child, opts) }
+    else
+      serializer.represent(hierarchy, opts)
+    end
+  end
+end
diff --git a/app/serializers/group_entity.rb b/app/serializers/group_entity.rb
index 7c872a3e986..6d8466da902 100644
--- a/app/serializers/group_entity.rb
+++ b/app/serializers/group_entity.rb
@@ -45,6 +45,6 @@ class GroupEntity < Grape::Entity
   end
 
   expose :avatar_url do |group|
-    group_icon(group)
+    group_icon_url(group)
   end
 end
diff --git a/app/serializers/group_serializer.rb b/app/serializers/group_serializer.rb
index 26e8566828b..8cf7eb63bcf 100644
--- a/app/serializers/group_serializer.rb
+++ b/app/serializers/group_serializer.rb
@@ -1,19 +1,5 @@
 class GroupSerializer < BaseSerializer
-  entity GroupEntity
-
-  def with_pagination(request, response)
-    tap { @paginator = Gitlab::Serializer::Pagination.new(request, response) }
-  end
+  include WithPagination
 
-  def paginated?
-    @paginator.present?
-  end
-
-  def represent(resource, opts = {})
-    if paginated?
-      super(@paginator.paginate(resource), opts)
-    else
-      super(resource, opts)
-    end
-  end
+  entity GroupEntity
 end
diff --git a/app/serializers/group_variable_entity.rb b/app/serializers/group_variable_entity.rb
new file mode 100644
index 00000000000..62cf0b21e1e
--- /dev/null
+++ b/app/serializers/group_variable_entity.rb
@@ -0,0 +1,7 @@
+class GroupVariableEntity < Grape::Entity
+  expose :id
+  expose :key
+  expose :value
+
+  expose :protected?, as: :protected
+end
diff --git a/app/serializers/group_variable_serializer.rb b/app/serializers/group_variable_serializer.rb
new file mode 100644
index 00000000000..8f8205924aa
--- /dev/null
+++ b/app/serializers/group_variable_serializer.rb
@@ -0,0 +1,3 @@
+class GroupVariableSerializer < BaseSerializer
+  entity GroupVariableEntity
+end
diff --git a/app/serializers/issuable_entity.rb b/app/serializers/issuable_entity.rb
index bd5211b8e58..6f31fbd6b7c 100644
--- a/app/serializers/issuable_entity.rb
+++ b/app/serializers/issuable_entity.rb
@@ -1,18 +1,8 @@
 class IssuableEntity < Grape::Entity
+  include RequestAwareEntity
+
   expose :id
   expose :iid
-  expose :author_id
   expose :description
-  expose :lock_version
-  expose :milestone_id
-  expose :state
   expose :title
-  expose :updated_by_id
-  expose :created_at
-  expose :updated_at
-  expose :deleted_at
-  expose :time_estimate
-  expose :total_time_spent
-  expose :human_time_estimate
-  expose :human_total_time_spent
 end
diff --git a/app/serializers/issuable_sidebar_entity.rb b/app/serializers/issuable_sidebar_entity.rb
new file mode 100644
index 00000000000..29138c803df
--- /dev/null
+++ b/app/serializers/issuable_sidebar_entity.rb
@@ -0,0 +1,12 @@
+class IssuableSidebarEntity < Grape::Entity
+  include TimeTrackableEntity
+  include RequestAwareEntity
+
+  expose :participants, using: ::API::Entities::UserBasic do |issuable|
+    issuable.participants(request.current_user)
+  end
+
+  expose :subscribed do |issuable|
+    issuable.subscribed?(request.current_user, issuable.project)
+  end
+end
diff --git a/app/serializers/issue_entity.rb b/app/serializers/issue_entity.rb
index 35df95549b7..b5e2334b6e3 100644
--- a/app/serializers/issue_entity.rb
+++ b/app/serializers/issue_entity.rb
@@ -1,16 +1,41 @@
 class IssueEntity < IssuableEntity
-  include RequestAwareEntity
+  include TimeTrackableEntity
 
-  expose :branch_name
+  expose :state
+  expose :milestone_id
+  expose :updated_by_id
+  expose :created_at
+  expose :updated_at
+  expose :milestone, using: API::Entities::Milestone
+  expose :labels, using: LabelEntity
+  expose :lock_version
+  expose :author_id
   expose :confidential
+  expose :discussion_locked
   expose :assignees, using: API::Entities::UserBasic
   expose :due_date
   expose :moved_to_id
   expose :project_id
-  expose :milestone, using: API::Entities::Milestone
-  expose :labels, using: LabelEntity
 
   expose :web_url do |issue|
-    namespace_project_issue_path(issue.project.namespace, issue.project, issue)
+    project_issue_path(issue.project, issue)
+  end
+
+  expose :current_user do
+    expose :can_create_note do |issue|
+      can?(request.current_user, :create_note, issue)
+    end
+
+    expose :can_update do |issue|
+      can?(request.current_user, :update_issue, issue)
+    end
+  end
+
+  expose :create_note_path do |issue|
+    project_notes_path(issue.project, target_type: 'issue', target_id: issue.id)
+  end
+
+  expose :preview_note_path do |issue|
+    preview_markdown_path(issue.project, quick_actions_target_type: 'Issue', quick_actions_target_id: issue.id)
   end
 end
diff --git a/app/serializers/issue_serializer.rb b/app/serializers/issue_serializer.rb
index 4fff54a9126..2555595379b 100644
--- a/app/serializers/issue_serializer.rb
+++ b/app/serializers/issue_serializer.rb
@@ -1,3 +1,16 @@
 class IssueSerializer < BaseSerializer
-  entity IssueEntity
+  # This overrided method takes care of which entity should be used
+  # to serialize the `issue` based on `basic` key in `opts` param.
+  # Hence, `entity` doesn't need to be declared on the class scope.
+  def represent(merge_request, opts = {})
+    entity =
+      case opts[:serializer]
+      when 'sidebar'
+        IssueSidebarEntity
+      else
+        IssueEntity
+      end
+
+    super(merge_request, opts, entity)
+  end
 end
diff --git a/app/serializers/issue_sidebar_entity.rb b/app/serializers/issue_sidebar_entity.rb
new file mode 100644
index 00000000000..6c823dbfe95
--- /dev/null
+++ b/app/serializers/issue_sidebar_entity.rb
@@ -0,0 +1,3 @@
+class IssueSidebarEntity < IssuableSidebarEntity
+  expose :assignees, using: API::Entities::UserBasic
+end
diff --git a/app/serializers/job_entity.rb b/app/serializers/job_entity.rb
index d6de43bcbcb..523b522d449 100644
--- a/app/serializers/job_entity.rb
+++ b/app/serializers/job_entity.rb
@@ -4,6 +4,8 @@ class JobEntity < Grape::Entity
   expose :id
   expose :name
 
+  expose :started?, as: :started
+
   expose :build_path do |build|
     build.target_url || path_to(:namespace_project_job, build)
   end
@@ -46,6 +48,6 @@ class JobEntity < Grape::Entity
   end
 
   def path_to(route, build)
-    send("#{route}_path", build.project.namespace, build.project, build)
+    send("#{route}_path", build.project.namespace, build.project, build) # rubocop:disable GitlabSecurity/PublicSend
   end
 end
diff --git a/app/serializers/label_entity.rb b/app/serializers/label_entity.rb
index ad565654342..4452161051e 100644
--- a/app/serializers/label_entity.rb
+++ b/app/serializers/label_entity.rb
@@ -1,5 +1,6 @@
 class LabelEntity < Grape::Entity
-  expose :id
+  expose :id, if: ->(label, _) { !label.is_a?(GlobalLabel) }
+
   expose :title
   expose :color
   expose :description
diff --git a/app/serializers/lfs_file_lock_entity.rb b/app/serializers/lfs_file_lock_entity.rb
new file mode 100644
index 00000000000..264a77adc3f
--- /dev/null
+++ b/app/serializers/lfs_file_lock_entity.rb
@@ -0,0 +1,11 @@
+class LfsFileLockEntity < Grape::Entity
+  root 'locks', 'lock'
+
+  expose :path
+  expose(:id) { |entity| entity.id.to_s }
+  expose(:created_at, as: :locked_at) { |entity| entity.created_at.to_s(:iso8601) }
+
+  expose :owner do
+    expose(:name) { |entity| entity.user&.name }
+  end
+end
diff --git a/app/serializers/lfs_file_lock_serializer.rb b/app/serializers/lfs_file_lock_serializer.rb
new file mode 100644
index 00000000000..ba8fb1a461d
--- /dev/null
+++ b/app/serializers/lfs_file_lock_serializer.rb
@@ -0,0 +1,3 @@
+class LfsFileLockSerializer < BaseSerializer
+  entity LfsFileLockEntity
+end
diff --git a/app/serializers/merge_request_basic_entity.rb b/app/serializers/merge_request_basic_entity.rb
index 8461f158bb5..e4aec977f01 100644
--- a/app/serializers/merge_request_basic_entity.rb
+++ b/app/serializers/merge_request_basic_entity.rb
@@ -1,11 +1,8 @@
-class MergeRequestBasicEntity < Grape::Entity
+class MergeRequestBasicEntity < IssuableSidebarEntity
   expose :assignee_id
   expose :merge_status
   expose :merge_error
   expose :state
   expose :source_branch_exists?, as: :source_branch_exists
-  expose :time_estimate
-  expose :total_time_spent
-  expose :human_time_estimate
-  expose :human_total_time_spent
+  expose :rebase_in_progress?, as: :rebase_in_progress
 end
diff --git a/app/serializers/merge_request_metrics_entity.rb b/app/serializers/merge_request_metrics_entity.rb
new file mode 100644
index 00000000000..3548107ac16
--- /dev/null
+++ b/app/serializers/merge_request_metrics_entity.rb
@@ -0,0 +1,6 @@
+class MergeRequestMetricsEntity < Grape::Entity
+  expose :latest_closed_at, as: :closed_at
+  expose :merged_at
+  expose :latest_closed_by, as: :closed_by, using: UserEntity
+  expose :merged_by, using: UserEntity
+end
diff --git a/app/serializers/merge_request_serializer.rb b/app/serializers/merge_request_serializer.rb
index f67034ce47a..caf193bdae3 100644
--- a/app/serializers/merge_request_serializer.rb
+++ b/app/serializers/merge_request_serializer.rb
@@ -1,9 +1,16 @@
 class MergeRequestSerializer < BaseSerializer
   # This overrided method takes care of which entity should be used
-  # to serialize the `merge_request` based on `basic` key in `opts` param.
+  # to serialize the `merge_request` based on `serializer` key in `opts` param.
   # Hence, `entity` doesn't need to be declared on the class scope.
   def represent(merge_request, opts = {})
-    entity = opts[:basic] ? MergeRequestBasicEntity : MergeRequestEntity
+    entity =
+      case opts[:serializer]
+      when 'basic', 'sidebar'
+        MergeRequestBasicEntity
+      else # It's 'widget'
+        MergeRequestWidgetEntity
+      end
+
     super(merge_request, opts, entity)
   end
 end
diff --git a/app/serializers/merge_request_entity.rb b/app/serializers/merge_request_widget_entity.rb
index 7bb981041cc..4a812e39ee1 100644
--- a/app/serializers/merge_request_entity.rb
+++ b/app/serializers/merge_request_widget_entity.rb
@@ -1,8 +1,6 @@
-class MergeRequestEntity < IssuableEntity
-  include RequestAwareEntity
-
+class MergeRequestWidgetEntity < IssuableEntity
+  expose :state
   expose :in_progress_merge_commit_sha
-  expose :locked_at
   expose :merge_commit_sha
   expose :merge_error
   expose :merge_params
@@ -13,32 +11,62 @@ class MergeRequestEntity < IssuableEntity
   expose :source_project_id
   expose :target_branch
   expose :target_project_id
+  expose :allow_maintainer_to_push
+
+  expose :should_be_rebased?, as: :should_be_rebased
+  expose :ff_only_enabled do |merge_request|
+    merge_request.project.merge_requests_ff_only_enabled
+  end
+
+  expose :metrics do |merge_request|
+    metrics = build_metrics(merge_request)
 
-  # Events
-  expose :merge_event, using: EventEntity
-  expose :closed_event, using: EventEntity
+    MergeRequestMetricsEntity.new(metrics).as_json
+  end
+
+  expose :rebase_commit_sha
+  expose :rebase_in_progress?, as: :rebase_in_progress
+
+  expose :can_push_to_source_branch do |merge_request|
+    presenter(merge_request).can_push_to_source_branch?
+  end
+
+  expose :rebase_path do |merge_request|
+    presenter(merge_request).rebase_path
+  end
 
   # User entities
-  expose :author, using: UserEntity
   expose :merge_user, using: UserEntity
 
   # Diff sha's
   expose :diff_head_sha do |merge_request|
-    merge_request.diff_head_sha if merge_request.diff_head_commit
+    merge_request.diff_head_sha.presence
   end
 
-  expose :merge_commit_sha
   expose :merge_commit_message
-  expose :head_pipeline, with: PipelineDetailsEntity, as: :pipeline
+  expose :actual_head_pipeline, with: PipelineDetailsEntity, as: :pipeline
 
   # Booleans
+  expose :merge_ongoing?, as: :merge_ongoing
   expose :work_in_progress?, as: :work_in_progress
   expose :source_branch_exists?, as: :source_branch_exists
-  expose :mergeable_discussions_state?, as: :mergeable_discussions_state
+
+  expose :mergeable_discussions_state?, as: :mergeable_discussions_state do |merge_request|
+    # This avoids calling MergeRequest#mergeable_discussions_state without
+    # considering the state of the MR first. If a MR isn't mergeable, we can
+    # safely short-circuit it.
+    if merge_request.mergeable_state?(skip_ci_check: true, skip_discussions_check: true)
+      merge_request.mergeable_discussions_state?
+    else
+      false
+    end
+  end
+
   expose :branch_missing?, as: :branch_missing
   expose :commits_count
   expose :cannot_be_merged?, as: :has_conflicts
   expose :can_be_merged?, as: :can_be_merged
+  expose :mergeable?, as: :mergeable
   expose :remove_source_branch?, as: :remove_source_branch
 
   expose :project_archived do |merge_request|
@@ -89,6 +117,14 @@ class MergeRequestEntity < IssuableEntity
     expose :can_cherry_pick_on_current_merge_request do |merge_request|
       presenter(merge_request).can_cherry_pick_on_current_merge_request?
     end
+
+    expose :can_create_note do |issue|
+      can?(request.current_user, :create_note, issue.project)
+    end
+
+    expose :can_update do |issue|
+      can?(request.current_user, :update_issue, issue)
+    end
   end
 
   # Paths
@@ -97,11 +133,13 @@ class MergeRequestEntity < IssuableEntity
     presenter(merge_request).target_branch_commits_path
   end
 
+  expose :target_branch_tree_path do |merge_request|
+    presenter(merge_request).target_branch_tree_path
+  end
+
   expose :new_blob_path do |merge_request|
-    if can?(current_user, :push_code, merge_request.project)
-      namespace_project_new_blob_path(merge_request.project.namespace,
-                                      merge_request.project,
-                                      merge_request.source_branch)
+    if presenter(merge_request).can_push_to_source_branch?
+      project_new_blob_path(merge_request.source_project, merge_request.source_branch)
     end
   end
 
@@ -134,30 +172,19 @@ class MergeRequestEntity < IssuableEntity
   end
 
   expose :email_patches_path do |merge_request|
-    namespace_project_merge_request_path(merge_request.project.namespace,
-                                         merge_request.project,
-                                         merge_request,
-                                         format: :patch)
+    project_merge_request_path(merge_request.project, merge_request, format: :patch)
   end
 
   expose :plain_diff_path do |merge_request|
-    namespace_project_merge_request_path(merge_request.project.namespace,
-                                         merge_request.project,
-                                         merge_request,
-                                         format: :diff)
+    project_merge_request_path(merge_request.project, merge_request, format: :diff)
   end
 
   expose :status_path do |merge_request|
-    namespace_project_merge_request_path(merge_request.target_project.namespace,
-                                         merge_request.target_project,
-                                         merge_request,
-                                         format: :json)
+    project_merge_request_path(merge_request.target_project, merge_request, format: :json)
   end
 
   expose :ci_environments_status_path do |merge_request|
-    ci_environments_status_namespace_project_merge_request_path(merge_request.project.namespace,
-                                                                merge_request.project,
-                                                                merge_request)
+    ci_environments_status_project_merge_request_path(merge_request.project, merge_request)
   end
 
   expose :merge_commit_message_with_description do |merge_request|
@@ -172,10 +199,12 @@ class MergeRequestEntity < IssuableEntity
     end
   end
 
+  expose :create_note_path do |merge_request|
+    project_notes_path(merge_request.project, target_type: 'merge_request', target_id: merge_request.id)
+  end
+
   expose :commit_change_content_path do |merge_request|
-    commit_change_content_namespace_project_merge_request_path(merge_request.project.namespace,
-                                                               merge_request.project,
-                                                               merge_request)
+    commit_change_content_project_merge_request_path(merge_request.project, merge_request)
   end
 
   private
@@ -186,4 +215,27 @@ class MergeRequestEntity < IssuableEntity
     @presenters ||= {}
     @presenters[merge_request] ||= MergeRequestPresenter.new(merge_request, current_user: current_user)
   end
+
+  # Once SchedulePopulateMergeRequestMetricsWithEventsData fully runs,
+  # we can remove this method and just serialize MergeRequest#metrics
+  # instead. See https://gitlab.com/gitlab-org/gitlab-ce/issues/41587
+  def build_metrics(merge_request)
+    # There's no need to query and serialize metrics data for merge requests that are not
+    # merged or closed.
+    return unless merge_request.merged? || merge_request.closed?
+    return merge_request.metrics if merge_request.merged? && merge_request.metrics&.merged_by_id
+    return merge_request.metrics if merge_request.closed? && merge_request.metrics&.latest_closed_by_id
+
+    build_metrics_from_events(merge_request)
+  end
+
+  def build_metrics_from_events(merge_request)
+    closed_event = merge_request.closed_event
+    merge_event = merge_request.merge_event
+
+    MergeRequest::Metrics.new(latest_closed_at: closed_event&.updated_at,
+                              latest_closed_by: closed_event&.author,
+                              merged_at: merge_event&.updated_at,
+                              merged_by: merge_event&.author)
+  end
 end
diff --git a/app/serializers/note_attachment_entity.rb b/app/serializers/note_attachment_entity.rb
new file mode 100644
index 00000000000..1ad50568ab9
--- /dev/null
+++ b/app/serializers/note_attachment_entity.rb
@@ -0,0 +1,5 @@
+class NoteAttachmentEntity < Grape::Entity
+  expose :url
+  expose :filename
+  expose :image?, as: :image
+end
diff --git a/app/serializers/note_entity.rb b/app/serializers/note_entity.rb
new file mode 100644
index 00000000000..4ccf0bca476
--- /dev/null
+++ b/app/serializers/note_entity.rb
@@ -0,0 +1,72 @@
+class NoteEntity < API::Entities::Note
+  include RequestAwareEntity
+
+  expose :type
+
+  expose :author, using: NoteUserEntity
+
+  expose :human_access do |note|
+    note.project.team.human_max_access(note.author_id)
+  end
+
+  unexpose :note, as: :body
+  expose :note
+
+  expose :redacted_note_html, as: :note_html
+
+  expose :last_edited_at, if: -> (note, _) { note.edited? }
+  expose :last_edited_by, using: NoteUserEntity, if: -> (note, _) { note.edited? }
+
+  expose :current_user do
+    expose :can_edit do |note|
+      Ability.can_edit_note?(request.current_user, note)
+    end
+  end
+
+  expose :resolved?, as: :resolved
+  expose :resolvable?, as: :resolvable
+  expose :resolved_by, using: NoteUserEntity
+
+  expose :system_note_icon_name, if: -> (note, _) { note.system? } do |note|
+    SystemNoteHelper.system_note_icon_name(note)
+  end
+
+  expose :discussion_id do |note|
+    note.discussion_id(request.noteable)
+  end
+
+  expose :emoji_awardable?, as: :emoji_awardable
+  expose :award_emoji, if: -> (note, _) { note.emoji_awardable? }, using: AwardEmojiEntity
+  expose :toggle_award_path, if: -> (note, _) { note.emoji_awardable? } do |note|
+    if note.for_personal_snippet?
+      toggle_award_emoji_snippet_note_path(note.noteable, note)
+    else
+      toggle_award_emoji_project_note_path(note.project, note.id)
+    end
+  end
+
+  expose :report_abuse_path do |note|
+    new_abuse_report_path(user_id: note.author.id, ref_url: Gitlab::UrlBuilder.build(note))
+  end
+
+  expose :path do |note|
+    if note.for_personal_snippet?
+      snippet_note_path(note.noteable, note)
+    else
+      project_note_path(note.project, note)
+    end
+  end
+
+  expose :resolve_path, if: -> (note, _) { note.part_of_discussion? && note.resolvable? } do |note|
+    resolve_project_merge_request_discussion_path(note.project, note.noteable, note.discussion_id)
+  end
+
+  expose :resolve_with_issue_path, if: -> (note, _) { note.part_of_discussion? && note.resolvable? } do |note|
+    new_project_issue_path(note.project, merge_request_to_resolve_discussions_of: note.noteable.iid, discussion_to_resolve: note.discussion_id)
+  end
+
+  expose :attachment, using: NoteAttachmentEntity, if: -> (note, _) { note.attachment? }
+  expose :delete_attachment_path, if: -> (note, _) { note.attachment? } do |note|
+    delete_attachment_project_note_path(note.project, note)
+  end
+end
diff --git a/app/serializers/note_serializer.rb b/app/serializers/note_serializer.rb
new file mode 100644
index 00000000000..2afe40d7a34
--- /dev/null
+++ b/app/serializers/note_serializer.rb
@@ -0,0 +1,3 @@
+class NoteSerializer < BaseSerializer
+  entity NoteEntity
+end
diff --git a/app/serializers/note_user_entity.rb b/app/serializers/note_user_entity.rb
new file mode 100644
index 00000000000..7289f3a0222
--- /dev/null
+++ b/app/serializers/note_user_entity.rb
@@ -0,0 +1,3 @@
+class NoteUserEntity < UserEntity
+  unexpose :web_url
+end
diff --git a/app/serializers/pipeline_entity.rb b/app/serializers/pipeline_entity.rb
index 6d1fd9d459f..6457294b285 100644
--- a/app/serializers/pipeline_entity.rb
+++ b/app/serializers/pipeline_entity.rb
@@ -10,18 +10,17 @@ class PipelineEntity < Grape::Entity
   expose :created_at, :updated_at
 
   expose :path do |pipeline|
-    namespace_project_pipeline_path(
-      pipeline.project.namespace,
-      pipeline.project,
-      pipeline)
+    project_pipeline_path(pipeline.project, pipeline)
   end
 
   expose :flags do
     expose :latest?, as: :latest
     expose :stuck?, as: :stuck
+    expose :auto_devops_source?, as: :auto_devops
     expose :has_yaml_errors?, as: :yaml_errors
     expose :can_retry?, as: :retryable
     expose :can_cancel?, as: :cancelable
+    expose :failure_reason?, as: :failure_reason
   end
 
   expose :details do
@@ -46,21 +45,20 @@ class PipelineEntity < Grape::Entity
   end
 
   expose :commit, using: CommitEntity
+  expose :yaml_errors, if: -> (pipeline, _) { pipeline.has_yaml_errors? }
+
+  expose :failure_reason, if: -> (pipeline, _) { pipeline.failure_reason? } do |pipeline|
+    pipeline.present.failure_reason
+  end
 
   expose :retry_path, if: -> (*) { can_retry? }  do |pipeline|
-    retry_namespace_project_pipeline_path(pipeline.project.namespace,
-                                          pipeline.project,
-                                          pipeline.id)
+    retry_project_pipeline_path(pipeline.project, pipeline)
   end
 
   expose :cancel_path, if: -> (*) { can_cancel? } do |pipeline|
-    cancel_namespace_project_pipeline_path(pipeline.project.namespace,
-                                           pipeline.project,
-                                           pipeline.id)
+    cancel_project_pipeline_path(pipeline.project, pipeline)
   end
 
-  expose :yaml_errors, if: -> (pipeline, _) { pipeline.has_yaml_errors? }
-
   private
 
   alias_method :pipeline, :object
diff --git a/app/serializers/pipeline_serializer.rb b/app/serializers/pipeline_serializer.rb
index 661bf17983c..7181f8a6b04 100644
--- a/app/serializers/pipeline_serializer.rb
+++ b/app/serializers/pipeline_serializer.rb
@@ -1,16 +1,10 @@
 class PipelineSerializer < BaseSerializer
+  include WithPagination
+
   InvalidResourceError = Class.new(StandardError)
 
   entity PipelineDetailsEntity
 
-  def with_pagination(request, response)
-    tap { @paginator = Gitlab::Serializer::Pagination.new(request, response) }
-  end
-
-  def paginated?
-    @paginator.present?
-  end
-
   def represent(resource, opts = {})
     if resource.is_a?(ActiveRecord::Relation)
 
diff --git a/app/serializers/project_entity.rb b/app/serializers/project_entity.rb
index a471a7e6a88..b3e5fd21e97 100644
--- a/app/serializers/project_entity.rb
+++ b/app/serializers/project_entity.rb
@@ -1,11 +1,11 @@
 class ProjectEntity < Grape::Entity
   include RequestAwareEntity
-  
+
   expose :id
   expose :name
 
   expose :full_path do |project|
-    namespace_project_path(project.namespace, project)
+    project_path(project)
   end
 
   expose :full_name do |project|
diff --git a/app/serializers/project_serializer.rb b/app/serializers/project_serializer.rb
new file mode 100644
index 00000000000..74de1e79a8f
--- /dev/null
+++ b/app/serializers/project_serializer.rb
@@ -0,0 +1,3 @@
+class ProjectSerializer < BaseSerializer
+  entity ProjectEntity
+end
diff --git a/app/serializers/runner_entity.rb b/app/serializers/runner_entity.rb
index ed7dacc2dbd..e9999a36d8a 100644
--- a/app/serializers/runner_entity.rb
+++ b/app/serializers/runner_entity.rb
@@ -5,7 +5,7 @@ class RunnerEntity < Grape::Entity
 
   expose :edit_path,
     if: -> (*) { can?(request.current_user, :admin_build, project) && runner.specific? } do |runner|
-    edit_namespace_project_runner_path(project.namespace, project, runner)
+    edit_project_runner_path(project, runner)
   end
 
   private
diff --git a/app/serializers/stage_entity.rb b/app/serializers/stage_entity.rb
index cee0089056f..4523b15152e 100644
--- a/app/serializers/stage_entity.rb
+++ b/app/serializers/stage_entity.rb
@@ -14,16 +14,14 @@ class StageEntity < Grape::Entity
   expose :detailed_status, as: :status, with: StatusEntity
 
   expose :path do |stage|
-    namespace_project_pipeline_path(
-      stage.pipeline.project.namespace,
+    project_pipeline_path(
       stage.pipeline.project,
       stage.pipeline,
       anchor: stage.name)
   end
 
   expose :dropdown_path do |stage|
-    stage_namespace_project_pipeline_path(
-      stage.pipeline.project.namespace,
+    stage_project_pipeline_path(
       stage.pipeline.project,
       stage.pipeline,
       stage: stage.name,
diff --git a/app/serializers/submodule_entity.rb b/app/serializers/submodule_entity.rb
new file mode 100644
index 00000000000..ed1f1ae0ef0
--- /dev/null
+++ b/app/serializers/submodule_entity.rb
@@ -0,0 +1,23 @@
+class SubmoduleEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :id, :path, :name, :mode
+
+  expose :icon do |blob|
+    'archive'
+  end
+
+  expose :url do |blob|
+    submodule_links(blob, request).first
+  end
+
+  expose :tree_url do |blob|
+    submodule_links(blob, request).last
+  end
+
+  private
+
+  def submodule_links(blob, request)
+    @submodule_links ||= SubmoduleHelper.submodule_links(blob, request.ref, request.repository)
+  end
+end
diff --git a/app/serializers/time_trackable_entity.rb b/app/serializers/time_trackable_entity.rb
new file mode 100644
index 00000000000..e81cd7bec72
--- /dev/null
+++ b/app/serializers/time_trackable_entity.rb
@@ -0,0 +1,11 @@
+module TimeTrackableEntity
+  extend ActiveSupport::Concern
+  extend Grape
+
+  included do
+    expose :time_estimate
+    expose :total_time_spent
+    expose :human_time_estimate
+    expose :human_total_time_spent
+  end
+end
diff --git a/app/serializers/tree_entity.rb b/app/serializers/tree_entity.rb
new file mode 100644
index 00000000000..9f1b485347f
--- /dev/null
+++ b/app/serializers/tree_entity.rb
@@ -0,0 +1,13 @@
+class TreeEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :id, :path, :name, :mode
+
+  expose :icon do |tree|
+    IconsHelper.file_type_icon_class('folder', tree.mode, tree.name)
+  end
+
+  expose :url do |tree|
+    project_tree_path(request.project, File.join(request.ref, tree.path))
+  end
+end
diff --git a/app/serializers/tree_root_entity.rb b/app/serializers/tree_root_entity.rb
new file mode 100644
index 00000000000..496f070ddbd
--- /dev/null
+++ b/app/serializers/tree_root_entity.rb
@@ -0,0 +1,25 @@
+# TODO: Inherit from TreeEntity, when `Tree` implements `id` and `name` like `Gitlab::Git::Tree`.
+class TreeRootEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :path
+
+  expose :trees, using: TreeEntity
+  expose :blobs, using: BlobEntity
+  expose :submodules, using: SubmoduleEntity
+
+  expose :parent_tree_url do |tree|
+    path = tree.path.sub(%r{\A/}, '')
+    next unless path.present?
+
+    path_segments = path.split('/')
+    path_segments.pop
+    parent_tree_path = path_segments.join('/')
+
+    project_tree_path(request.project, File.join(request.ref, parent_tree_path))
+  end
+
+  expose :last_commit_path do |tree|
+    logs_file_project_ref_path(request.project, request.ref, tree.path)
+  end
+end
diff --git a/app/serializers/tree_serializer.rb b/app/serializers/tree_serializer.rb
new file mode 100644
index 00000000000..713ade23bc9
--- /dev/null
+++ b/app/serializers/tree_serializer.rb
@@ -0,0 +1,3 @@
+class TreeSerializer < BaseSerializer
+  entity TreeRootEntity
+end
diff --git a/app/serializers/user_serializer.rb b/app/serializers/user_serializer.rb
new file mode 100644
index 00000000000..49a71ebac61
--- /dev/null
+++ b/app/serializers/user_serializer.rb
@@ -0,0 +1,3 @@
+class UserSerializer < BaseSerializer
+  entity UserEntity
+end
diff --git a/app/serializers/variable_entity.rb b/app/serializers/variable_entity.rb
new file mode 100644
index 00000000000..d576745c073
--- /dev/null
+++ b/app/serializers/variable_entity.rb
@@ -0,0 +1,7 @@
+class VariableEntity < Grape::Entity
+  expose :id
+  expose :key
+  expose :value
+
+  expose :protected?, as: :protected
+end
diff --git a/app/serializers/variable_serializer.rb b/app/serializers/variable_serializer.rb
new file mode 100644
index 00000000000..32ae82ab51c
--- /dev/null
+++ b/app/serializers/variable_serializer.rb
@@ -0,0 +1,3 @@
+class VariableSerializer < BaseSerializer
+  entity VariableEntity
+end