Split MR widget into cached and non-cached serializers

Splits auto-refreshing of MR widget into 2 requests:

- the one which uses etag-caching and invalidates the fields on change
- the one without caching

The idea is to gradually move all the fields to etag-cached endpoint

4 files changed, 281 insertions, 250 deletions

diff --git a/app/serializers/merge_request_poll_cached_widget_entity.rb b/app/serializers/merge_request_poll_cached_widget_entity.rb
new file mode 100644
index 00000000000..005a3e47bbb
--- /dev/null
+++ b/app/serializers/merge_request_poll_cached_widget_entity.rb
@@ -0,0 +1,103 @@
+# frozen_string_literal: true
+
+class MergeRequestPollCachedWidgetEntity < IssuableEntity
+  expose :auto_merge_enabled
+  expose :state
+  expose :merge_commit_sha
+  expose :short_merge_commit_sha
+  expose :merge_error
+  expose :merge_status
+  expose :merge_user_id
+  expose :source_branch
+  expose :source_project_id
+  expose :target_branch
+  expose :target_branch_sha
+  expose :target_project_id
+  expose :squash
+  expose :rebase_in_progress?, as: :rebase_in_progress
+  expose :default_squash_commit_message
+  expose :commits_count
+  expose :merge_ongoing?, as: :merge_ongoing
+  expose :work_in_progress?, as: :work_in_progress
+  expose :cannot_be_merged?, as: :has_conflicts
+  expose :can_be_merged?, as: :can_be_merged
+  expose :remove_source_branch?, as: :remove_source_branch
+  expose :source_branch_exists?, as: :source_branch_exists
+  expose :branch_missing?, as: :branch_missing
+
+  expose :commits_without_merge_commits, using: MergeRequestWidgetCommitEntity do |merge_request|
+    merge_request.commits.without_merge_commits
+  end
+  expose :diff_head_sha do |merge_request|
+    merge_request.diff_head_sha.presence
+  end
+  expose :metrics do |merge_request|
+    metrics = build_metrics(merge_request)
+
+    MergeRequestMetricsEntity.new(metrics).as_json
+  end
+
+  expose :diverged_commits_count do |merge_request|
+    if merge_request.open? && merge_request.diverged_from_target_branch?
+      merge_request.diverged_commits_count
+    else
+      0
+    end
+  end
+
+  # Paths
+  #
+  expose :target_branch_commits_path do |merge_request|
+    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 :merge_commit_path do |merge_request|
+    if merge_request.merge_commit_sha
+      project_commit_path(merge_request.project, merge_request.merge_commit_sha)
+    end
+  end
+
+  expose :source_branch_path do |merge_request|
+    presenter(merge_request).source_branch_path
+  end
+
+  expose :source_branch_with_namespace_link do |merge_request|
+    presenter(merge_request).source_branch_with_namespace_link
+  end
+
+  private
+
+  delegate :current_user, to: :request
+
+  def presenter(merge_request)
+    @presenters ||= {}
+    @presenters[merge_request] ||= MergeRequestPresenter.new(merge_request, current_user: current_user) # rubocop: disable CodeReuse/Presenter
+  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/merge_request_poll_widget_entity.rb b/app/serializers/merge_request_poll_widget_entity.rb
new file mode 100644
index 00000000000..65132b4b215
--- /dev/null
+++ b/app/serializers/merge_request_poll_widget_entity.rb
@@ -0,0 +1,142 @@
+# frozen_string_literal: true
+
+class MergeRequestPollWidgetEntity < IssuableEntity
+  expose :auto_merge_strategy
+  expose :available_auto_merge_strategies do |merge_request|
+    AutoMergeService.new(merge_request.project, current_user).available_strategies(merge_request) # rubocop: disable CodeReuse/ServiceClass
+  end
+  expose :source_branch_protected do |merge_request|
+    merge_request.source_project.present? && ProtectedBranch.protected?(merge_request.source_project, merge_request.source_branch)
+  end
+  expose :allow_collaboration
+  expose :should_be_rebased?, as: :should_be_rebased
+  expose :ff_only_enabled do |merge_request|
+    merge_request.project.merge_requests_ff_only_enabled
+  end
+
+  # User entities
+  expose :merge_user, using: UserEntity
+
+  expose :actual_head_pipeline, with: PipelineDetailsEntity, as: :pipeline, if: -> (mr, _) { presenter(mr).can_read_pipeline? }
+
+  expose :merge_pipeline, with: PipelineDetailsEntity, if: ->(mr, _) { mr.merged? && can?(request.current_user, :read_pipeline, mr.target_project)}
+
+  expose :default_merge_commit_message
+
+  expose :mergeable?, as: :mergeable
+
+  expose :default_merge_commit_message_with_description do |merge_request|
+    merge_request.default_merge_commit_message(include_description: true)
+  end
+
+  # Booleans
+  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 :project_archived do |merge_request|
+    merge_request.project.archived?
+  end
+
+  expose :only_allow_merge_if_pipeline_succeeds do |merge_request|
+    merge_request.project.only_allow_merge_if_pipeline_succeeds?
+  end
+
+  # CI related
+  expose :has_ci?, as: :has_ci
+  expose :ci_status do |merge_request|
+    presenter(merge_request).ci_status
+  end
+
+  expose :cancel_auto_merge_path do |merge_request|
+    presenter(merge_request).cancel_auto_merge_path
+  end
+
+  expose :test_reports_path do |merge_request|
+    if merge_request.has_test_reports?
+      test_reports_project_merge_request_path(merge_request.project, merge_request, format: :json)
+    end
+  end
+
+  expose :supports_suggestion?, as: :can_receive_suggestion
+
+  expose :create_issue_to_resolve_discussions_path do |merge_request|
+    presenter(merge_request).create_issue_to_resolve_discussions_path
+  end
+
+  expose :current_user do
+    expose :can_remove_source_branch do |merge_request|
+      presenter(merge_request).can_remove_source_branch?
+    end
+
+    expose :can_revert_on_current_merge_request do |merge_request|
+      presenter(merge_request).can_revert_on_current_merge_request?
+    end
+
+    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 |merge_request|
+      can?(current_user, :create_note, merge_request)
+    end
+
+    expose :can_create_issue do |merge_request|
+      can?(current_user, :create_issue, merge_request.project)
+    end
+
+    expose :can_update do |merge_request|
+      can?(current_user, :update_merge_request, merge_request)
+    end
+  end
+
+  expose :can_push_to_source_branch do |merge_request|
+    presenter(merge_request).can_push_to_source_branch?
+  end
+
+  expose :new_blob_path do |merge_request|
+    if presenter(merge_request).can_push_to_source_branch?
+      project_new_blob_path(merge_request.source_project, merge_request.source_branch)
+    end
+  end
+
+  expose :rebase_path do |merge_request|
+    presenter(merge_request).rebase_path
+  end
+
+  expose :conflict_resolution_path do |merge_request|
+    presenter(merge_request).conflict_resolution_path
+  end
+
+  expose :remove_wip_path do |merge_request|
+    presenter(merge_request).remove_wip_path
+  end
+
+  expose :merge_path do |merge_request|
+    presenter(merge_request).merge_path
+  end
+
+  expose :cherry_pick_in_fork_path do |merge_request|
+    presenter(merge_request).cherry_pick_in_fork_path
+  end
+
+  expose :revert_in_fork_path do |merge_request|
+    presenter(merge_request).revert_in_fork_path
+  end
+
+  private
+
+  delegate :current_user, to: :request
+
+  def presenter(merge_request)
+    @presenters ||= {}
+    @presenters[merge_request] ||= MergeRequestPresenter.new(merge_request, current_user: current_user) # rubocop: disable CodeReuse/Presenter
+  end
+end
diff --git a/app/serializers/merge_request_serializer.rb b/app/serializers/merge_request_serializer.rb
index 6f589351670..8ad1df5dfe0 100644
--- a/app/serializers/merge_request_serializer.rb
+++ b/app/serializers/merge_request_serializer.rb
@@ -4,8 +4,8 @@ class MergeRequestSerializer < BaseSerializer
   # This overrided method takes care of which entity should be used
   # 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 =
+  def represent(merge_request, opts = {}, entity = nil)
+    entity ||=
       case opts[:serializer]
       when 'sidebar'
         IssuableSidebarBasicEntity
diff --git a/app/serializers/merge_request_widget_entity.rb b/app/serializers/merge_request_widget_entity.rb
index fd2673fa0cc..554b307d4f8 100644
--- a/app/serializers/merge_request_widget_entity.rb
+++ b/app/serializers/merge_request_widget_entity.rb
@@ -1,117 +1,62 @@
 # frozen_string_literal: true
 
-class MergeRequestWidgetEntity < IssuableEntity
-  expose :state
-  expose :in_progress_merge_commit_sha
-  expose :merge_commit_sha
-  expose :short_merge_commit_sha
-  expose :merge_error
+class MergeRequestWidgetEntity < Grape::Entity
+  include RequestAwareEntity
+
+  # Currently this attr is exposed to be used in app/assets/javascripts/notes/stores/getters.js
+  # in order to determine whether a noteable is an issue or an MR
   expose :merge_params
-  expose :merge_status
-  expose :merge_user_id
-  expose :auto_merge_enabled
-  expose :auto_merge_strategy
-  expose :available_auto_merge_strategies do |merge_request|
-    AutoMergeService.new(merge_request.project, current_user).available_strategies(merge_request) # rubocop: disable CodeReuse/ServiceClass
-  end
-  expose :source_branch
-  expose :source_branch_protected do |merge_request|
-    merge_request.source_project.present? && ProtectedBranch.protected?(merge_request.source_project, merge_request.source_branch)
-  end
-  expose :source_project_id
+
   expose :source_project_full_path do |merge_request|
     merge_request.source_project&.full_path
   end
-  expose :squash
-  expose :target_branch
-  expose :target_branch_sha
-  expose :target_project_id
+
   expose :target_project_full_path do |merge_request|
     merge_request.project&.full_path
   end
-  expose :allow_collaboration
 
-  expose :should_be_rebased?, as: :should_be_rebased
-  expose :ff_only_enabled do |merge_request|
-    merge_request.project.merge_requests_ff_only_enabled
+  expose :email_patches_path do |merge_request|
+    project_merge_request_path(merge_request.project, merge_request, format: :patch)
   end
 
-  expose :metrics do |merge_request|
-    metrics = build_metrics(merge_request)
-
-    MergeRequestMetricsEntity.new(metrics).as_json
+  expose :plain_diff_path do |merge_request|
+    project_merge_request_path(merge_request.project, merge_request, format: :diff)
   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?
+  expose :merge_request_basic_path do |merge_request|
+    project_merge_request_path(merge_request.target_project, merge_request, serializer: :basic, format: :json)
   end
 
-  expose :rebase_path do |merge_request|
-    presenter(merge_request).rebase_path
+  expose :merge_request_widget_path do |merge_request|
+    widget_project_json_merge_request_path(merge_request.target_project, merge_request, format: :json)
   end
 
-  # User entities
-  expose :merge_user, using: UserEntity
-
-  # Diff sha's
-  expose :diff_head_sha do |merge_request|
-    merge_request.diff_head_sha.presence
+  expose :merge_request_cached_widget_path do |merge_request|
+    cached_widget_project_json_merge_request_path(merge_request.target_project, merge_request, format: :json)
   end
 
-  expose :actual_head_pipeline, with: PipelineDetailsEntity, as: :pipeline, if: -> (mr, _) { presenter(mr).can_read_pipeline? }
-
-  expose :merge_pipeline, with: PipelineDetailsEntity, if: ->(mr, _) { mr.merged? && can?(request.current_user, :read_pipeline, mr.target_project)}
-
-  expose :default_squash_commit_message
-  expose :default_merge_commit_message
-
-  expose :default_merge_commit_message_with_description do |merge_request|
-    merge_request.default_merge_commit_message(include_description: true)
+  expose :create_note_path do |merge_request|
+    project_notes_path(merge_request.project, target_type: 'merge_request', target_id: merge_request.id)
   end
 
-  expose :commits_without_merge_commits, using: MergeRequestWidgetCommitEntity do |merge_request|
-    merge_request.commits.without_merge_commits
+  expose :commit_change_content_path do |merge_request|
+    commit_change_content_project_merge_request_path(merge_request.project, merge_request)
   end
 
-  expose :commits_count
-
-  # 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 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
+  expose :preview_note_path do |merge_request|
+    preview_markdown_path(merge_request.project, target_type: 'MergeRequest', target_id: merge_request.iid)
   end
 
-  expose :branch_missing?, as: :branch_missing
-  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|
-    merge_request.project.archived?
+  expose :conflicts_docs_path do |merge_request|
+    help_page_path('user/project/merge_requests/resolve_conflicts.md')
   end
 
-  expose :only_allow_merge_if_pipeline_succeeds do |merge_request|
-    merge_request.project.only_allow_merge_if_pipeline_succeeds?
+  expose :merge_request_pipelines_docs_path do |merge_request|
+    help_page_path('ci/merge_request_pipelines/index.md')
   end
 
-  # CI related
-  expose :has_ci?, as: :has_ci
-  expose :ci_status do |merge_request|
-    presenter(merge_request).ci_status
+  expose :ci_environments_status_path do |merge_request|
+    ci_environments_status_project_merge_request_path(merge_request.project, merge_request)
   end
 
   # Rendering and redacting Markdown can be expensive. These links are
@@ -131,175 +76,16 @@ class MergeRequestWidgetEntity < IssuableEntity
     end
   end
 
-  expose :source_branch_with_namespace_link do |merge_request|
-    presenter(merge_request).source_branch_with_namespace_link
-  end
-
-  expose :source_branch_path do |merge_request|
-    presenter(merge_request).source_branch_path
-  end
-
-  expose :current_user do
-    expose :can_remove_source_branch do |merge_request|
-      presenter(merge_request).can_remove_source_branch?
-    end
-
-    expose :can_revert_on_current_merge_request do |merge_request|
-      presenter(merge_request).can_revert_on_current_merge_request?
-    end
-
-    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 |merge_request|
-      can?(request.current_user, :create_note, merge_request)
-    end
-
-    expose :can_create_issue do |merge_request|
-      can?(current_user, :create_issue, merge_request.project)
-    end
-
-    expose :can_update do |merge_request|
-      can?(request.current_user, :update_merge_request, merge_request)
-    end
-  end
-
-  # Paths
-  #
-  expose :target_branch_commits_path do |merge_request|
-    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 presenter(merge_request).can_push_to_source_branch?
-      project_new_blob_path(merge_request.source_project, merge_request.source_branch)
-    end
-  end
-
-  expose :conflict_resolution_path do |merge_request|
-    presenter(merge_request).conflict_resolution_path
-  end
-
-  expose :remove_wip_path do |merge_request|
-    presenter(merge_request).remove_wip_path
-  end
-
-  expose :cancel_auto_merge_path do |merge_request|
-    presenter(merge_request).cancel_auto_merge_path
-  end
-
-  expose :create_issue_to_resolve_discussions_path do |merge_request|
-    presenter(merge_request).create_issue_to_resolve_discussions_path
-  end
-
-  expose :merge_path do |merge_request|
-    presenter(merge_request).merge_path
-  end
-
-  expose :cherry_pick_in_fork_path do |merge_request|
-    presenter(merge_request).cherry_pick_in_fork_path
-  end
-
-  expose :revert_in_fork_path do |merge_request|
-    presenter(merge_request).revert_in_fork_path
-  end
-
-  expose :email_patches_path do |merge_request|
-    project_merge_request_path(merge_request.project, merge_request, format: :patch)
-  end
-
-  expose :plain_diff_path do |merge_request|
-    project_merge_request_path(merge_request.project, merge_request, format: :diff)
-  end
-
-  expose :merge_request_basic_path do |merge_request|
-    project_merge_request_path(merge_request.target_project, merge_request, serializer: :basic, format: :json)
-  end
-
-  expose :merge_request_widget_path do |merge_request|
-    widget_project_json_merge_request_path(merge_request.target_project, merge_request, format: :json)
-  end
-
-  expose :ci_environments_status_path do |merge_request|
-    ci_environments_status_project_merge_request_path(merge_request.project, merge_request)
-  end
-
-  expose :diverged_commits_count do |merge_request|
-    if merge_request.open? && merge_request.diverged_from_target_branch?
-      merge_request.diverged_commits_count
-    else
-      0
-    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_project_merge_request_path(merge_request.project, merge_request)
-  end
-
-  expose :preview_note_path do |merge_request|
-    preview_markdown_path(merge_request.project, target_type: 'MergeRequest', target_id: merge_request.iid)
-  end
-
-  expose :merge_commit_path do |merge_request|
-    if merge_request.merge_commit_sha
-      project_commit_path(merge_request.project, merge_request.merge_commit_sha)
-    end
-  end
-
-  expose :test_reports_path do |merge_request|
-    if merge_request.has_test_reports?
-      test_reports_project_merge_request_path(merge_request.project, merge_request, format: :json)
-    end
-  end
-
-  expose :supports_suggestion?, as: :can_receive_suggestion
-
-  expose :conflicts_docs_path do |merge_request|
-    presenter(merge_request).conflicts_docs_path
-  end
-
-  expose :merge_request_pipelines_docs_path do |merge_request|
-    presenter(merge_request).merge_request_pipelines_docs_path
+  def as_json(options = {})
+    super(options)
+      .merge(MergeRequestPollCachedWidgetEntity.new(object, **@options.opts_hash).as_json(options))
+      .merge(MergeRequestPollWidgetEntity.new(object, **@options.opts_hash).as_json(options))
   end
 
   private
 
-  delegate :current_user, to: :request
-
   def presenter(merge_request)
     @presenters ||= {}
-    @presenters[merge_request] ||= MergeRequestPresenter.new(merge_request, current_user: current_user) # rubocop: disable CodeReuse/Presenter
-  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)
+    @presenters[merge_request] ||= MergeRequestPresenter.new(merge_request, current_user: request.current_user) # rubocop: disable CodeReuse/Presenter
   end
 end