Add mutation to create a new branch in GraphQL

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/215617

app/graphql/mutations/branches/create.rb

+# frozen_string_literal: true
+
+module Mutations
+  module Branches
+    class Create < BaseMutation
+      include Mutations::ResolvesProject
+
+      graphql_name 'CreateBranch'
+
+      argument :project_path, GraphQL::ID_TYPE,
+               required: true,
+               description: 'Project full path the branch is associated with'
+
+      argument :name, GraphQL::STRING_TYPE,
+               required: true,
+               description: 'Name of the branch'
+
+      argument :ref,
+               GraphQL::STRING_TYPE,
+               required: true,
+               description: 'Branch name or commit SHA to create branch from'
+
+      field :branch,
+            Types::BranchType,
+            null: true,
+            description: 'Branch after mutation'
+
+      authorize :push_code
+
+      def resolve(project_path:, name:, ref:)
+        project = authorized_find!(full_path: project_path)
+
+        context.scoped_set!(:branch_project, project)
+
+        result = ::Branches::CreateService.new(project, current_user)
+                   .execute(name, ref)
+
+        {
+          branch: (result[:branch] if result[:status] == :success),
+          errors: Array.wrap(result[:message])
+        }
+      end
+
+      private
+
+      def find_object(full_path:)
+        resolve_project(full_path: full_path)
+      end
+    end
+  end
+end

app/graphql/resolvers/branch_commit_resolver.rb

+# frozen_string_literal: true
+
+module Resolvers
+  class BranchCommitResolver < BaseResolver
+    type Types::CommitType, null: true
+
+    alias_method :branch, :object
+
+    def resolve(**args)
+      return unless branch
+
+      commit = branch.dereferenced_target
+
+      ::Commit.new(commit, context[:branch_project]) if commit
+    end
+  end
+end

app/graphql/types/branch_type.rb

+# frozen_string_literal: true
+
+module Types
+  # rubocop: disable Graphql/AuthorizeTypes
+  class BranchType < BaseObject
+    graphql_name 'Branch'
+
+    field :name,
+          GraphQL::STRING_TYPE,
+          null: false,
+          description: 'Name of the branch'
+
+    field :commit, Types::CommitType,
+          null: true, resolver: Resolvers::BranchCommitResolver,
+          description: 'Commit for the branch'
+  end
+  # rubocop: enable Graphql/AuthorizeTypes
+end

app/graphql/types/mutation_type.rb

@@ -10,6 +10,7 @@ module Types
     mount_mutation Mutations::AwardEmojis::Add
     mount_mutation Mutations::AwardEmojis::Remove
     mount_mutation Mutations::AwardEmojis::Toggle
+    mount_mutation Mutations::Branches::Create, calls_gitaly: true
     mount_mutation Mutations::Issues::SetConfidential
     mount_mutation Mutations::Issues::SetDueDate
     mount_mutation Mutations::Issues::Update

changelogs/unreleased/215617_mutation_to_add_a_new_branch.yml

+---
+title: Add mutation to create a new branch in GraphQL
+merge_request: 30388
+author:
+type: added

doc/api/graphql/reference/gitlab_schema.graphql

@@ -651,6 +651,18 @@ type BoardListUpdateLimitMetricsPayload {
   list: BoardList
 }
 
+type Branch {
+  """
+  Commit for the branch
+  """
+  commit: Commit
+
+  """
+  Name of the branch
+  """
+  name: String!
+}
+
 type Commit {
   """
   Author of the commit
@@ -768,6 +780,51 @@ type Commit {
   webUrl: String!
 }
 
+"""
+Autogenerated input type of CreateBranch
+"""
+input CreateBranchInput {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  Name of the branch
+  """
+  name: String!
+
+  """
+  Project full path the branch is associated with
+  """
+  projectPath: ID!
+
+  """
+  Branch name or commit SHA to create branch from
+  """
+  ref: String!
+}
+
+"""
+Autogenerated return type of CreateBranch
+"""
+type CreateBranchPayload {
+  """
+  Branch after mutation
+  """
+  branch: Branch
+
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  Reasons why the mutation failed.
+  """
+  errors: [String!]!
+}
+
 """
 Autogenerated input type of CreateDiffNote
 """
@@ -5975,6 +6032,7 @@ type Mutation {
   addProjectsToSecurityDashboard(input: AddProjectsToSecurityDashboardInput!): AddProjectsToSecurityDashboardPayload
   adminSidekiqQueuesDeleteJobs(input: AdminSidekiqQueuesDeleteJobsInput!): AdminSidekiqQueuesDeleteJobsPayload
   boardListUpdateLimitMetrics(input: BoardListUpdateLimitMetricsInput!): BoardListUpdateLimitMetricsPayload
+  createBranch(input: CreateBranchInput!): CreateBranchPayload
   createDiffNote(input: CreateDiffNoteInput!): CreateDiffNotePayload
   createEpic(input: CreateEpicInput!): CreateEpicPayload
   createImageDiffNote(input: CreateImageDiffNoteInput!): CreateImageDiffNotePayload

doc/api/graphql/reference/gitlab_schema.json

@@ -1903,6 +1903,51 @@
           "enumValues": null,
           "possibleTypes": null
         },
+        {
+          "kind": "OBJECT",
+          "name": "Branch",
+          "description": null,
+          "fields": [
+            {
+              "name": "commit",
+              "description": "Commit for the branch",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "Commit",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "name",
+              "description": "Name of the branch",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "String",
+                  "ofType": null
+                }
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            }
+          ],
+          "inputFields": null,
+          "interfaces": [
+
+          ],
+          "enumValues": null,
+          "possibleTypes": null
+        },
         {
           "kind": "OBJECT",
           "name": "Commit",
@@ -2208,6 +2253,136 @@
           "enumValues": null,
           "possibleTypes": null
         },
+        {
+          "kind": "INPUT_OBJECT",
+          "name": "CreateBranchInput",
+          "description": "Autogenerated input type of CreateBranch",
+          "fields": null,
+          "inputFields": [
+            {
+              "name": "projectPath",
+              "description": "Project full path the branch is associated with",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "ID",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "name",
+              "description": "Name of the branch",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "String",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "ref",
+              "description": "Branch name or commit SHA to create branch from",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "String",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "clientMutationId",
+              "description": "A unique identifier for the client performing the mutation.",
+              "type": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              },
+              "defaultValue": null
+            }
+          ],
+          "interfaces": null,
+          "enumValues": null,
+          "possibleTypes": null
+        },
+        {
+          "kind": "OBJECT",
+          "name": "CreateBranchPayload",
+          "description": "Autogenerated return type of CreateBranch",
+          "fields": [
+            {
+              "name": "branch",
+              "description": "Branch after mutation",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "Branch",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "clientMutationId",
+              "description": "A unique identifier for the client performing the mutation.",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "errors",
+              "description": "Reasons why the mutation failed.",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "LIST",
+                  "name": null,
+                  "ofType": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "SCALAR",
+                      "name": "String",
+                      "ofType": null
+                    }
+                  }
+                }
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            }
+          ],
+          "inputFields": null,
+          "interfaces": [
+
+          ],
+          "enumValues": null,
+          "possibleTypes": null
+        },
         {
           "kind": "INPUT_OBJECT",
           "name": "CreateDiffNoteInput",
@@ -17134,6 +17309,33 @@
               "isDeprecated": false,
               "deprecationReason": null
             },
+            {
+              "name": "createBranch",
+              "description": null,
+              "args": [
+                {
+                  "name": "input",
+                  "description": null,
+                  "type": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "INPUT_OBJECT",
+                      "name": "CreateBranchInput",
+                      "ofType": null
+                    }
+                  },
+                  "defaultValue": null
+                }
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "CreateBranchPayload",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
             {
               "name": "createDiffNote",
               "description": null,

doc/api/graphql/reference/index.md

@@ -135,6 +135,13 @@ Autogenerated return type of BoardListUpdateLimitMetrics
 | `errors` | String! => Array | Reasons why the mutation failed. |
 | `list` | BoardList | The updated list |
 
+## Branch
+
+| Name  | Type  | Description |
+| ---   |  ---- | ----------  |
+| `commit` | Commit | Commit for the branch |
+| `name` | String! | Name of the branch |
+
 ## Commit
 
 | Name  | Type  | Description |
@@ -152,6 +159,16 @@ Autogenerated return type of BoardListUpdateLimitMetrics
 | `title` | String | Title of the commit message |
 | `webUrl` | String! | Web URL of the commit |
 
+## CreateBranchPayload
+
+Autogenerated return type of CreateBranch
+
+| Name  | Type  | Description |
+| ---   |  ---- | ----------  |
+| `branch` | Branch | Branch after mutation |
+| `clientMutationId` | String | A unique identifier for the client performing the mutation. |
+| `errors` | String! => Array | Reasons why the mutation failed. |
+
 ## CreateDiffNotePayload
 
 Autogenerated return type of CreateDiffNote

spec/graphql/mutations/branches/create_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Mutations::Branches::Create do
+  subject(:mutation) { described_class.new(object: nil, context: context, field: nil) }
+
+  let_it_be(:project) { create(:project, :public, :repository) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:context) do
+    GraphQL::Query::Context.new(
+      query: OpenStruct.new(schema: nil),
+      values: { current_user: user },
+      object: nil
+    )
+  end
+
+  describe '#resolve' do
+    subject { mutation.resolve(project_path: project.full_path, name: branch, ref: ref) }
+
+    let(:branch) { 'new_branch' }
+    let(:ref) { 'master' }
+    let(:mutated_branch) { subject[:branch] }
+
+    it 'raises an error if the resource is not accessible to the user' do
+      expect { subject }.to raise_error(Gitlab::Graphql::Errors::ResourceNotAvailable)
+    end
+
+    context 'when the user can create a branch' do
+      before do
+        project.add_developer(user)
+
+        allow_next_instance_of(::Branches::CreateService, project, user) do |create_service|
+          allow(create_service).to receive(:execute).with(branch, ref) { service_result }
+        end
+      end
+
+      context 'when service successfully creates a new branch' do
+        let(:service_result) { { status: :success, branch: double(name: branch) } }
+
+        it 'returns a new branch' do
+          expect(mutated_branch.name).to eq(branch)
+          expect(subject[:errors]).to be_empty
+        end
+      end
+
+      context 'when service fails to create a new branch' do
+        let(:service_result) { { status: :error, message: 'Branch already exists' } }
+
+        it { expect(mutated_branch).to be_nil }
+        it { expect(subject[:errors]).to eq(['Branch already exists']) }
+      end
+    end
+  end
+end

spec/graphql/resolvers/branch_commit_resolver_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Resolvers::BranchCommitResolver do
+  include GraphqlHelpers
+
+  subject(:commit) { resolve(described_class, obj: branch) }
+
+  let_it_be(:repository) { create(:project, :repository).repository }
+  let(:branch) { repository.find_branch('master') }
+
+  describe '#resolve' do
+    it 'resolves commit' do
+      is_expected.to eq(repository.commits('master', limit: 1).last)
+    end
+
+    context 'when branch does not exist' do
+      let(:branch) { nil }
+
+      it 'returns nil' do
+        is_expected.to be_nil
+      end
+    end
+  end
+end

spec/graphql/types/branch_type_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe GitlabSchema.types['Branch'] do
+  it { expect(described_class.graphql_name).to eq('Branch') }
+
+  it { expect(described_class).to have_graphql_fields(:name, :commit) }
+end

spec/requests/api/graphql/mutations/branches/create_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Creation of a new branch' do
+  include GraphqlHelpers
+
+  let_it_be(:current_user) { create(:user) }
+  let(:project) { create(:project, :public, :repository) }
+  let(:input) { { project_path: project.full_path, name: new_branch, ref: ref } }
+  let(:new_branch) { 'new_branch' }
+  let(:ref) { 'master' }
+
+  let(:mutation) { graphql_mutation(:create_branch, input) }
+  let(:mutation_response) { graphql_mutation_response(:create_branch) }
+
+  context 'the user is not allowed to create a branch' do
+    it_behaves_like 'a mutation that returns top-level errors',
+      errors: ['The resource that you are attempting to access does not exist or you don\'t have permission to perform this action']
+  end
+
+  context 'when user has permissions to create a branch' do
+    before do
+      project.add_developer(current_user)
+    end
+
+    it 'creates a new branch' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_response['branch']).to include(
+        'name' => new_branch,
+        'commit' => a_hash_including('id')
+      )
+    end
+
+    context 'when ref is not correct' do
+      let(:ref) { 'unknown' }
+
+      it_behaves_like 'a mutation that returns errors in the response',
+                      errors: ['Invalid reference name: new_branch']
+    end
+  end
+end