Optionally include trailers in the commits API

This adds the `trailers` option to the project commits API. When
enabled, Gitaly will parse the Git trailers into a structured object,
which is then presented in the API response.

The API to obtain merge request commits doesn't support this option at
this time. Said API retrieves data from the database. The Gitaly RPC
used to populate that data doesn't support parsing Git trailers at this
time, and extending it will likely require a fair amount of work. As
such, we only extend the regular commits API for the time being.

See https://gitlab.com/gitlab-org/release-tools/-/merge_requests/1464
and https://gitlab.com/gitlab-org/release-tools/-/issues/500 for more
information.

Changelog: added

doc/api/commits.md

@@ -28,6 +28,7 @@ GET /projects/:id/repository/commits
 | `with_stats` | boolean | no | Stats about each commit are added to the response |
 | `first_parent` | boolean | no | Follow only the first parent commit upon seeing a merge commit |
 | `order` | string | no | List commits in order. Possible values: `default`, [`topo`](https://git-scm.com/docs/git-log#Documentation/git-log.txt---topo-order). Defaults to `default`, the commits are shown in reverse chronological order. |
+| `trailers` | boolean | no | Parse and include [Git trailers](https://git-scm.com/docs/git-interpret-trailers) for every commit |
 
 ```shell
 curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/projects/5/repository/commits"

lib/api/commits.rb

 # frozen_string_literal: true
-
 require 'mime/types'
 
 module API
@@ -41,6 +40,7 @@ module API
         optional :with_stats, type: Boolean, desc: 'Stats about each commit will be added to the response'
         optional :first_parent, type: Boolean, desc: 'Only include the first parent of merges'
         optional :order, type: String, desc: 'List commits in order', default: 'default', values: %w[default topo]
+        optional :trailers, type: Boolean, desc: 'Parse and include Git trailers for every commit', default: false
         use :pagination
       end
       get ':id/repository/commits' do
@@ -62,7 +62,8 @@ module API
                                                   after: after,
                                                   all: all,
                                                   first_parent: first_parent,
-                                                  order: order)
+                                                  order: order,
+                                                  trailers: params[:trailers])
 
         serializer = with_stats ? Entities::CommitWithStats : Entities::Commit
 

lib/api/entities/commit.rb

@@ -9,6 +9,7 @@ module API
       expose :safe_message, as: :message
       expose :author_name, :author_email, :authored_date
       expose :committer_name, :committer_email, :committed_date
+      expose :trailers
 
       expose :web_url do |commit, _options|
         Gitlab::UrlBuilder.build(commit)

spec/requests/api/commits_spec.rb

@@ -284,6 +284,18 @@ RSpec.describe API::Commits do
           end
         end
       end
+
+      context 'with the optional trailers parameter' do
+        it 'includes the Git trailers' do
+          get api("/projects/#{project_id}/repository/commits?ref_name=6d394385cf567f80a8fd85055db1ab4c5295806f&trailers=true", current_user)
+
+          commit = json_response[0]
+
+          expect(commit['trailers']).to eq(
+            'Signed-off-by' => 'Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>'
+          )
+        end
+      end
     end
   end