Use "branch_name" instead "branch" on V3 branch creation API

changelogs/unreleased/29604-v3-fix-branch-creation.yml

+---
+title: Use "branch_name" instead "branch" on V3 branch creation API
+merge_request:
+author:

lib/api/v3/branches.rb

@@ -45,6 +45,27 @@ module API
 
           status(200)
         end
+
+        desc 'Create branch' do
+          success ::API::Entities::RepoBranch
+        end
+        params do
+          requires :branch_name, type: String, desc: 'The name of the branch'
+          requires :ref, type: String, desc: 'Create branch from commit sha or existing branch'
+        end
+        post ":id/repository/branches" do
+          authorize_push_project
+          result = CreateBranchService.new(user_project, current_user).
+            execute(params[:branch_name], params[:ref])
+
+          if result[:status] == :success
+            present result[:branch],
+              with: ::API::Entities::RepoBranch,
+              project: user_project
+          else
+            render_api_error!(result[:message], 400)
+          end
+        end
       end
     end
   end

spec/requests/api/v3/branches_spec.rb

@@ -10,6 +10,7 @@ describe API::V3::Branches, api: true  do
   let!(:master) { create(:project_member, :master, user: user, project: project) }
   let!(:guest) { create(:project_member, :guest, user: user2, project: project) }
   let!(:branch_name) { 'feature' }
+  let!(:branch_sha) { '0b4bc9a49b562e85de7cc9e834518ea6828729b9' }
   let!(:branch_with_dot) { CreateBranchService.new(project, user).execute("with.1.2.3", "master") }
 
   describe "GET /projects/:id/repository/branches" do
@@ -80,4 +81,55 @@ describe API::V3::Branches, api: true  do
       expect(response).to have_http_status(403)
     end
   end
+
+  describe "POST /projects/:id/repository/branches" do
+    it "creates a new branch" do
+      post v3_api("/projects/#{project.id}/repository/branches", user),
+           branch_name: 'feature1',
+           ref: branch_sha
+
+      expect(response).to have_http_status(201)
+
+      expect(json_response['name']).to eq('feature1')
+      expect(json_response['commit']['id']).to eq(branch_sha)
+    end
+
+    it "denies for user without push access" do
+      post v3_api("/projects/#{project.id}/repository/branches", user2),
+           branch_name: branch_name,
+           ref: branch_sha
+      expect(response).to have_http_status(403)
+    end
+
+    it 'returns 400 if branch name is invalid' do
+      post v3_api("/projects/#{project.id}/repository/branches", user),
+           branch_name: 'new design',
+           ref: branch_sha
+      expect(response).to have_http_status(400)
+      expect(json_response['message']).to eq('Branch name is invalid')
+    end
+
+    it 'returns 400 if branch already exists' do
+      post v3_api("/projects/#{project.id}/repository/branches", user),
+           branch_name: 'new_design1',
+           ref: branch_sha
+      expect(response).to have_http_status(201)
+
+      post v3_api("/projects/#{project.id}/repository/branches", user),
+           branch_name: 'new_design1',
+           ref: branch_sha
+
+      expect(response).to have_http_status(400)
+      expect(json_response['message']).to eq('Branch already exists')
+    end
+
+    it 'returns 400 if ref name is invalid' do
+      post v3_api("/projects/#{project.id}/repository/branches", user),
+           branch_name: 'new_design3',
+           ref: 'foo'
+
+      expect(response).to have_http_status(400)
+      expect(json_response['message']).to eq('Invalid reference name')
+    end
+  end
 end