Adds API feature configuring default mr target

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/343909

Changelog: added

app/models/project.rb

@@ -436,6 +436,7 @@ class Project < ApplicationRecord
     prefix: :import, to: :import_state, allow_nil: true
   delegate :squash_always?, :squash_never?, :squash_enabled_by_default?, :squash_readonly?, to: :project_setting
   delegate :squash_option, :squash_option=, to: :project_setting
+  delegate :mr_default_target_self, :mr_default_target_self=, to: :project_setting
   delegate :previous_default_branch, :previous_default_branch=, to: :project_setting
   delegate :no_import?, to: :import_state, allow_nil: true
   delegate :name, to: :owner, allow_nil: true, prefix: true

app/models/project_setting.rb

@@ -22,6 +22,16 @@ class ProjectSetting < ApplicationRecord
   def squash_readonly?
     %w[always never].include?(squash_option)
   end
+
+  validate :validates_mr_default_target_self
+
+  private
+
+  def validates_mr_default_target_self
+    if mr_default_target_self_changed? && !project.forked?
+      errors.add :mr_default_target_self, _('This setting is allowed for forked projects only')
+    end
+  end
 end
 
 ProjectSetting.prepend_mod

app/services/projects/fork_service.rb

@@ -69,6 +69,8 @@ module Projects
         new_params[:avatar] = @project.avatar
       end
 
+      new_params[:mr_default_target_self] = target_mr_default_target_self unless target_mr_default_target_self.nil?
+
       new_params.merge!(@project.object_pool_params)
 
       new_params
@@ -127,5 +129,9 @@ module Projects
 
       Gitlab::VisibilityLevel.closest_allowed_level(target_level)
     end
+
+    def target_mr_default_target_self
+      @target_mr_default_target_self ||= params[:mr_default_target_self]
+    end
   end
 end

doc/api/projects.md

@@ -1049,8 +1049,10 @@ The `web_url` and `avatar_url` attributes on `namespace` were
 [introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/27427)
 in GitLab 11.11.
 
-If the project is a fork, and you provide a valid token to authenticate, the
-`forked_from_project` field appears in the response.
+If the project is a fork, the `forked_from_project` field appears in the response.
+For this field, if the upstream project is private, a valid token for authentication must be provided.
+The field `mr_default_target_self` appears as well. If this value is `false`, then all merge requests
+will target the upstream project by default.
 
 ```json
 {
@@ -1058,6 +1060,7 @@ If the project is a fork, and you provide a valid token to authenticate, the
 
    ...
 
+   "mr_default_target_self": false,
    "forked_from_project":{
       "id":13083,
       "description":"GitLab Community Edition",
@@ -1448,6 +1451,7 @@ Supported attributes:
 | `issues_template` **(PREMIUM)**                             | string         | **{dotted-circle}** No | Default description for Issues. Description is parsed with GitLab Flavored Markdown. See [Templates for issues and merge requests](#templates-for-issues-and-merge-requests). |
 | `merge_requests_template` **(PREMIUM)**                     | string         | **{dotted-circle}** No | Default description for Merge Requests. Description is parsed with GitLab Flavored Markdown. See [Templates for issues and merge requests](#templates-for-issues-and-merge-requests). |
 | `keep_latest_artifact`                                      | boolean        | **{dotted-circle}** No | Disable or enable the ability to keep the latest artifact for this project. |
+| `mr_default_target_self`                                    | boolean        | **{dotted-circle}** No | For forked projects, target merge requests to this project. If `false`, the target will be the upstream project. |
 
 ## Fork project
 
@@ -1471,6 +1475,7 @@ POST /projects/:id/fork
 | `path`           | string         | **{dotted-circle}** No | The path assigned to the resultant project after forking.                        |
 | `description`    | string         | **{dotted-circle}** No | The description assigned to the resultant project after forking.                 |
 | `visibility`     | string         | **{dotted-circle}** No | The [visibility level](#project-visibility-level) assigned to the resultant project after forking. |
+| `mr_default_target_self` | boolean | **{dotted-circle}** No | For forked projects, target merge requests to this project. If `false`, the target will be the upstream project. |
 
 ## List Forks of a project
 

lib/api/entities/project.rb

@@ -82,6 +82,8 @@ module API
       expose :forked_from_project, using: Entities::BasicProjectDetails, if: ->(project, options) do
         project.forked? && Ability.allowed?(options[:current_user], :read_project, project.forked_from_project)
       end
+      expose :mr_default_target_self, if: -> (project) { project.forked? }
+
       expose :import_status
 
       expose :import_error, if: lambda { |_project, options| options[:user_can_admin_project] } do |project|

lib/api/helpers/projects_helpers.rb

@@ -71,6 +71,7 @@ module API
         optional :repository_storage, type: String, desc: 'Which storage shard the repository is on. Available only to admins'
         optional :packages_enabled, type: Boolean, desc: 'Enable project packages feature'
         optional :squash_option, type: String, values: %w(never always default_on default_off), desc: 'Squash default for project. One of `never`, `always`, `default_on`, or `default_off`.'
+        optional :mr_default_target_self, Boolean, desc: 'Merge requests of this forked project targets itself by default'
       end
 
       params :optional_project_params_ee do
@@ -169,6 +170,7 @@ module API
           :packages_enabled,
           :service_desk_enabled,
           :keep_latest_artifact,
+          :mr_default_target_self,
 
           # TODO: remove in API v5, replaced by *_access_level
           :issues_enabled,

lib/api/projects.rb

@@ -363,6 +363,7 @@ module API
         optional :name, type: String, desc: 'The name that will be assigned to the fork'
         optional :description, type: String, desc: 'The description that will be assigned to the fork'
         optional :visibility, type: String, values: Gitlab::VisibilityLevel.string_values, desc: 'The visibility of the fork'
+        optional :mr_default_target_self, Boolean, desc: 'Merge requests of this forked project targets itself by default'
       end
       post ':id/fork', feature_category: :source_code_management do
         Gitlab::QueryLimiting.disable!('https://gitlab.com/gitlab-org/gitlab/-/issues/20759')

locale/gitlab.pot

@@ -36289,6 +36289,9 @@ msgstr ""
 msgid "This setting can be overridden in each project."
 msgstr ""
 
+msgid "This setting is allowed for forked projects only"
+msgstr ""
+
 msgid "This subscription is for"
 msgstr ""
 

spec/requests/api/projects_spec.rb

@@ -3681,6 +3681,46 @@ RSpec.describe API::Projects do
         expect { subject }.to change { project.reload.keep_latest_artifact }.to(true)
       end
     end
+
+    context 'attribute mr_default_target_self' do
+      let_it_be(:source_project) { create(:project, :public) }
+
+      let(:forked_project) { fork_project(source_project, user) }
+
+      it 'is by default set to false' do
+        expect(source_project.mr_default_target_self).to be false
+        expect(forked_project.mr_default_target_self).to be false
+      end
+
+      describe 'for a non-forked project' do
+        before_all do
+          source_project.add_maintainer(user)
+        end
+
+        it 'is not exposed' do
+          get api("/projects/#{source_project.id}", user)
+
+          expect(json_response).not_to include('mr_default_target_self')
+        end
+
+        it 'is not possible to update' do
+          put api("/projects/#{source_project.id}", user), params: { mr_default_target_self: true }
+
+          source_project.reload
+          expect(source_project.mr_default_target_self).to be false
+          expect(response).to have_gitlab_http_status(:bad_request)
+        end
+      end
+
+      describe 'for a forked project' do
+        it 'updates to true' do
+          put api("/projects/#{forked_project.id}", user), params: { mr_default_target_self: true }
+
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(json_response['mr_default_target_self']).to eq(true)
+        end
+      end
+    end
   end
 
   describe 'POST /projects/:id/archive' do
@@ -4190,7 +4230,13 @@ RSpec.describe API::Projects do
       end
 
       it 'accepts custom parameters for the target project' do
-        post api("/projects/#{project.id}/fork", user2), params: { name: 'My Random Project', description: 'A description', visibility: 'private' }
+        post api("/projects/#{project.id}/fork", user2),
+          params: {
+            name: 'My Random Project',
+            description: 'A description',
+            visibility: 'private',
+            mr_default_target_self: true
+          }
 
         expect(response).to have_gitlab_http_status(:created)
         expect(json_response['name']).to eq('My Random Project')
@@ -4201,6 +4247,7 @@ RSpec.describe API::Projects do
         expect(json_response['description']).to eq('A description')
         expect(json_response['visibility']).to eq('private')
         expect(json_response['import_status']).to eq('scheduled')
+        expect(json_response['mr_default_target_self']).to eq(true)
         expect(json_response).to include("import_error")
       end