Fix API bug accepting wrong merge requests parameters

changelogs/unreleased/issue_33205.yml

+---
+title: Fix API bug accepting wrong parameter to create merge request
+merge_request:
+author:

lib/api/merge_requests.rb

@@ -97,7 +97,7 @@ module API
         authorize! :create_merge_request, user_project
 
         mr_params = declared_params(include_missing: false)
-        mr_params[:force_remove_source_branch] = mr_params.delete(:remove_source_branch) if mr_params[:remove_source_branch].present?
+        mr_params[:force_remove_source_branch] = mr_params.delete(:remove_source_branch)
 
         merge_request = ::MergeRequests::CreateService.new(user_project, current_user, mr_params).execute
 

spec/requests/api/merge_requests_spec.rb

@@ -334,14 +334,13 @@ describe API::MergeRequests do
              target_branch: 'master',
              author: user,
              labels: 'label, label2',
-             milestone_id: milestone.id,
-             remove_source_branch: true
+             milestone_id: milestone.id
 
         expect(response).to have_http_status(201)
         expect(json_response['title']).to eq('Test merge_request')
         expect(json_response['labels']).to eq(%w(label label2))
         expect(json_response['milestone']['id']).to eq(milestone.id)
-        expect(json_response['force_remove_source_branch']).to be_truthy
+        expect(json_response['force_remove_source_branch']).to be_falsy
       end
 
       it "returns 422 when source_branch equals target_branch" do
@@ -404,6 +403,27 @@ describe API::MergeRequests do
           expect(response).to have_http_status(409)
         end
       end
+
+      context 'accepts remove_source_branch parameter' do
+        let(:params) do
+          { title: 'Test merge_request',
+            source_branch: 'markdown',
+            target_branch: 'master',
+            author: user }
+        end
+
+        it 'sets force_remove_source_branch to false' do
+          post api("/projects/#{project.id}/merge_requests", user), params.merge(remove_source_branch: false)
+
+          expect(json_response['force_remove_source_branch']).to be_falsy
+        end
+
+        it 'sets force_remove_source_branch to true' do
+          post api("/projects/#{project.id}/merge_requests", user), params.merge(remove_source_branch: true)
+
+          expect(json_response['force_remove_source_branch']).to be_truthy
+        end
+      end
     end
 
     context 'forked projects' do