Remove unused data from discussions endpoint

We don't need a series of attributes to render diff files on
discussions.json request. Therefore this MR removes lots of unnecessary
attributes from the request, mainly the highlighted diff lines, which
are pretty expensive.

1 files changed, 101 insertions, 0 deletions

diff --git a/app/serializers/diff_file_base_entity.rb b/app/serializers/diff_file_base_entity.rb
new file mode 100644
index 00000000000..06a8db78476
--- /dev/null
+++ b/app/serializers/diff_file_base_entity.rb
@@ -0,0 +1,101 @@
+# frozen_string_literal: true
+
+class DiffFileBaseEntity < Grape::Entity
+  include RequestAwareEntity
+  include BlobHelper
+  include SubmoduleHelper
+  include DiffHelper
+  include TreeHelper
+  include ChecksCollaboration
+  include Gitlab::Utils::StrongMemoize
+
+  expose :content_sha
+  expose :submodule?, as: :submodule
+
+  expose :submodule_link do |diff_file|
+    memoized_submodule_links(diff_file).first
+  end
+
+  expose :submodule_tree_url do |diff_file|
+    memoized_submodule_links(diff_file).last
+  end
+
+  expose :edit_path, if: -> (_, options) { options[:merge_request] } do |diff_file|
+    merge_request = options[:merge_request]
+
+    options = merge_request.persisted? ? { from_merge_request_iid: merge_request.iid } : {}
+
+    next unless merge_request.source_project
+
+    project_edit_blob_path(merge_request.source_project,
+      tree_join(merge_request.source_branch, diff_file.new_path),
+      options)
+  end
+
+  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
+
+  expose :formatted_external_url, if: -> (_, options) { options[:environment] } do |diff_file|
+    options[:environment].formatted_external_url
+  end
+
+  expose :external_url, if: -> (_, options) { options[:environment] } do |diff_file|
+    options[:environment].external_url_for(diff_file.new_path, diff_file.content_sha)
+  end
+
+  expose :blob, using: BlobEntity
+
+  expose :can_modify_blob do |diff_file|
+    merge_request = options[:merge_request]
+
+    next unless diff_file.blob
+
+    if merge_request&.source_project && current_user
+      can_modify_blob?(diff_file.blob, merge_request.source_project, merge_request.source_branch)
+    else
+      false
+    end
+  end
+
+  expose :file_hash do |diff_file|
+    Digest::SHA1.hexdigest(diff_file.file_path)
+  end
+
+  expose :file_path
+  expose :old_path
+  expose :new_path
+  expose :new_file?, as: :new_file
+  expose :collapsed?, as: :collapsed
+  expose :text?, as: :text
+  expose :diff_refs
+  expose :stored_externally?, as: :stored_externally
+  expose :external_storage
+  expose :renamed_file?, as: :renamed_file
+  expose :deleted_file?, as: :deleted_file
+  expose :mode_changed?, as: :mode_changed
+  expose :a_mode
+  expose :b_mode
+
+  private
+
+  def memoized_submodule_links(diff_file)
+    strong_memoize(:submodule_links) do
+      if diff_file.submodule?
+        submodule_links(diff_file.blob, diff_file.content_sha, diff_file.repository)
+      else
+        []
+      end
+    end
+  end
+
+  def current_user
+    request.current_user
+  end
+end