Find branches in all projects in the fork network

app/controllers/projects/merge_requests/creations_controller.rb

@@ -122,10 +122,13 @@ class Projects::MergeRequests::CreationsController < Projects::MergeRequests::Ap
   end
 
   def selected_target_project
-    if @project.id.to_s == params[:target_project_id] || @project.forked_project_link.nil?
+    if @project.id.to_s == params[:target_project_id] || !@project.forked?
       @project
+    elsif params[:target_project_id].present?
+      MergeRequestTargetProjectFinder.new(current_user: current_user, source_project: @project)
+        .execute.find(params[:target_project_id])
     else
-      @project.forked_project_link.forked_from_project
+      @project.forked_from_project
     end
   end
 end

app/finders/merge_request_target_project_finder.rb

 class MergeRequestTargetProjectFinder
   attr_reader :current_user, :source_project
 
-  def initialize(current_user: nil, source_project:, params: {})
+  def initialize(current_user: nil, source_project:)
     @current_user = current_user
     @source_project = source_project
   end

spec/features/merge_requests/create_new_mr_from_fork_spec.rb

@@ -44,6 +44,25 @@ feature 'Creating a merge request from a fork', :js do
       expect { click_button 'Submit merge request' }
         .to change { target_project.merge_requests.reload.size }.by(1)
     end
+
+    it 'updates the branches when selecting a new target project' do
+      target_project_member = target_project.owner
+      CreateBranchService.new(target_project, target_project_member)
+        .execute('a-brand-new-branch-to-test', 'master')
+
+      visit project_new_merge_request_path(source_project)
+
+      first('.js-target-project').click
+      find('.dropdown-target-project .dropdown-content a', text: target_project.full_path).click
+
+      wait_for_requests
+
+      first('.js-target-branch').click
+
+      within('.dropdown-target-branch .dropdown-content') do
+        expect(page).to have_content('a-brand-new-branch-to-test')
+      end
+    end
   end
 
   context 'creating to the source of a fork' do