Expose first_contribution for merge request API

Only for getting a single merge request

changelogs/unreleased/24742-1st-contribution.yml

+---
+title: Add first_contribution to single merge request API
+merge_request: 26926
+author:
+type: added

doc/api/merge_requests.md

@@ -668,6 +668,7 @@ dependent on the `merge_status`. It'll return `false` unless `merge_status` is
   },
   "diverged_commits_count": 2,
   "rebase_in_progress": false,
+  "first_contribution": false,
   "task_completion_status":{
     "count":0,
     "completed_count":0

lib/api/entities/merge_request.rb

@@ -39,6 +39,16 @@ module API
 
       expose :diverged_commits_count, as: :diverged_commits_count, if: -> (_, options) { options[:include_diverged_commits_count] }
 
+      # We put this into an option because list of TODOs API will attach their
+      # targets with Entities::MergeRequest instead of
+      # Entities::MergeRequestBasic, but this attribute cannot be eagerly
+      # loaded in batch for now. The list of merge requests API will
+      # use Entities::MergeRequestBasic which does not support this, and
+      # we always enable this for the single merge request API. This way
+      # we avoid N+1 queries in the TODOs API and can still enable it for
+      # the single merge request API.
+      expose :first_contribution?, as: :first_contribution, if: -> (_, options) { options[:include_first_contribution] }
+
       def build_available?(options)
         options[:project]&.feature_available?(:builds, options[:current_user])
       end

lib/api/merge_requests.rb

@@ -267,6 +267,7 @@ module API
           current_user: current_user,
           project: user_project,
           render_html: params[:render_html],
+          include_first_contribution: true,
           include_diverged_commits_count: params[:include_diverged_commits_count],
           include_rebase_in_progress: params[:include_rebase_in_progress]
       end

spec/requests/api/merge_requests_spec.rb

@@ -892,6 +892,7 @@ describe API::MergeRequests do
       expect(json_response['merge_error']).to eq(merge_request.merge_error)
       expect(json_response['user']['can_merge']).to be_truthy
       expect(json_response).not_to include('rebase_in_progress')
+      expect(json_response['first_contribution']).to be_falsy
       expect(json_response['has_conflicts']).to be_falsy
       expect(json_response['blocking_discussions_resolved']).to be_truthy
       expect(json_response['references']['short']).to eq("!#{merge_request.iid}")
@@ -915,6 +916,21 @@ describe API::MergeRequests do
       expect(json_response).to include('rebase_in_progress')
     end
 
+    context 'when author is not a member without any merged merge requests' do
+      let(:non_member) { create(:user) }
+
+      before do
+        merge_request.update(author: non_member)
+      end
+
+      it 'exposes first_contribution as true' do
+        get api("/projects/#{project.id}/merge_requests/#{merge_request.iid}", user)
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(json_response['first_contribution']).to be_truthy
+      end
+    end
+
     context 'merge_request_metrics' do
       let(:pipeline) { create(:ci_empty_pipeline) }