Add a simple mode to merge request API

The current "basic" merge request API still loads too much data. For integrations
like the Trello Power-up, we just need the basics.

Closes #34920

changelogs/unreleased/sh-add-mr-simple-mode.yml

+---
+title: Add a simple mode to merge request API
+merge_request:
+author:

doc/api/merge_requests.md

@@ -25,6 +25,7 @@ Parameters:
 | `order_by`| string  | no    | Return requests ordered by `created_at` or `updated_at` fields. Default is `created_at` |
 | `sort`    | string  | no    | Return requests sorted in `asc` or `desc` order. Default is `desc`  |
 | `milestone`  | string  | no | Return merge requests for a specific milestone |
+| `simple` | boolean | no | Returns the `iid`, URL, title, description, and basic state of merge request |
 | `labels`  | string  | no | Return merge requests matching a comma separated list of labels |
 | `created_after` | datetime | no | Return merge requests created after the given time (inclusive) |
 | `created_before` | datetime | no | Return merge requests created before the given time (inclusive) |

lib/api/entities.rb

@@ -314,6 +314,13 @@ module API
       expose :id
     end
 
+    class MergeRequestSimple < ProjectEntity
+      expose :title
+      expose :web_url do |merge_request, options|
+        Gitlab::UrlBuilder.build(merge_request)
+      end
+    end
+
     class MergeRequestBasic < ProjectEntity
       expose :target_branch, :source_branch
       expose :upvotes do |merge_request, options|

lib/api/merge_requests.rb

@@ -44,9 +44,14 @@ module API
           args[:label_name] = args.delete(:labels)
 
           merge_requests = MergeRequestsFinder.new(current_user, args).execute
-          merge_requests = merge_requests.reorder(args[:order_by] => args[:sort])
-          paginate(merge_requests)
-            .preload(:notes, :target_project, :author, :assignee, :milestone, :merge_request_diff, :labels)
+                             .reorder(args[:order_by] => args[:sort])
+          merge_requests = paginate(merge_requests)
+                             .preload(:target_project)
+
+          return merge_requests if params[:simple]
+
+          merge_requests
+            .preload(:notes, :author, :assignee, :milestone, :merge_request_diff, :labels)
         end
 
         params :optional_params_ce do
@@ -77,15 +82,25 @@ module API
         optional :labels, type: String, desc: 'Comma-separated list of label names'
         optional :created_after, type: DateTime, desc: 'Return merge requests created after the specified time'
         optional :created_before, type: DateTime, desc: 'Return merge requests created before the specified time'
+        optional :simple, type: Boolean, default: false, desc: 'Returns the `iid`, URL, title, description, and basic state of merge request'
         use :pagination
       end
       get ":id/merge_requests" do
         authorize! :read_merge_request, user_project
 
         merge_requests = find_merge_requests(project_id: user_project.id)
-        issuable_metadata = issuable_meta_data(merge_requests, 'MergeRequest')
 
-        present merge_requests, with: Entities::MergeRequestBasic, current_user: current_user, project: user_project, issuable_metadata: issuable_metadata
+        options = { with: Entities::MergeRequestBasic,
+                    current_user: current_user,
+                    project: user_project }
+
+        if params[:simple]
+          options[:with] = Entities::MergeRequestSimple
+        else
+          options[:issuable_metadata] = issuable_meta_data(merge_requests, 'MergeRequest')
+        end
+
+        present merge_requests, options
       end
 
       desc 'Create a merge request' do

spec/requests/api/merge_requests_spec.rb

@@ -69,6 +69,22 @@ describe API::MergeRequests do
         expect(json_response.first['merge_commit_sha']).to eq(merge_request_merged.merge_commit_sha)
       end
 
+      it "returns an array of all merge_requests using simple mode" do
+        get api("/projects/#{project.id}/merge_requests?simple=true", user)
+
+        expect(response).to have_http_status(200)
+        expect(response).to include_pagination_headers
+        expect(json_response.last.keys).to match_array(%w(id iid title web_url created_at description project_id state updated_at))
+        expect(json_response).to be_an Array
+        expect(json_response.length).to eq(3)
+        expect(json_response.last['iid']).to eq(merge_request.iid)
+        expect(json_response.last['title']).to eq(merge_request.title)
+        expect(json_response.last).to have_key('web_url')
+        expect(json_response.first['iid']).to eq(merge_request_merged.iid)
+        expect(json_response.first['title']).to eq(merge_request_merged.title)
+        expect(json_response.first).to have_key('web_url')
+      end
+
       it "returns an array of all merge_requests" do
         get api("/projects/#{project.id}/merge_requests?state", user)