GraphQL: Add MRSetLabels mutation

Add a mutation to set labels on a Merge Request.

If `append` is true, only appends labels
If `remove` is true, only removes labels

Otherwise the list sent becomes the only labels applied

app/graphql/mutations/merge_requests/set_labels.rb

+# frozen_string_literal: true
+
+module Mutations
+  module MergeRequests
+    class SetLabels < Base
+      graphql_name 'MergeRequestSetLabels'
+
+      argument :label_ids,
+               [GraphQL::ID_TYPE],
+               required: true,
+               description: <<~DESC
+                            The Label IDs to set. Replaces existing labels by default.
+               DESC
+
+      argument :operation_mode,
+               Types::MutationOperationModeEnum,
+               required: false,
+               description: <<~DESC
+                            Changes the operation mode. Defaults to REPLACE.
+               DESC
+
+      def resolve(project_path:, iid:, label_ids:, operation_mode: Types::MutationOperationModeEnum.enum[:replace])
+        merge_request = authorized_find!(project_path: project_path, iid: iid)
+        project = merge_request.project
+
+        label_ids = label_ids
+                      .select(&method(:label_descendant?))
+                      .map { |gid| GlobalID.parse(gid).model_id } # MergeRequests::UpdateService expects integers
+
+        attribute_name = case operation_mode
+                         when Types::MutationOperationModeEnum.enum[:append]
+                           :add_label_ids
+                         when Types::MutationOperationModeEnum.enum[:remove]
+                           :remove_label_ids
+                         else
+                           :label_ids
+                         end
+
+        ::MergeRequests::UpdateService.new(project, current_user, attribute_name => label_ids)
+          .execute(merge_request)
+
+        {
+          merge_request: merge_request,
+          errors: merge_request.errors.full_messages
+        }
+      end
+
+      def label_descendant?(gid)
+        GlobalID.parse(gid)&.model_class&.ancestors&.include?(Label)
+      end
+    end
+  end
+end

app/graphql/types/label_type.rb

@@ -6,6 +6,8 @@ module Types
 
     authorize :read_label
 
+    field :id, GraphQL::ID_TYPE, null: false,
+          description: 'Label ID'
     field :description, GraphQL::STRING_TYPE, null: true,
           description: 'Description of the label (markdown rendered as HTML for caching)'
     markdown_field :description_html, null: true

app/graphql/types/mutation_type.rb

@@ -9,6 +9,7 @@ module Types
     mount_mutation Mutations::AwardEmojis::Add
     mount_mutation Mutations::AwardEmojis::Remove
     mount_mutation Mutations::AwardEmojis::Toggle
+    mount_mutation Mutations::MergeRequests::SetLabels
     mount_mutation Mutations::MergeRequests::SetMilestone
     mount_mutation Mutations::MergeRequests::SetWip, calls_gitaly: true
     mount_mutation Mutations::MergeRequests::SetAssignees

spec/graphql/mutations/merge_requests/set_labels_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Mutations::MergeRequests::SetLabels do
+  let(:merge_request) { create(:merge_request) }
+  let(:user) { create(:user) }
+  subject(:mutation) { described_class.new(object: nil, context: { current_user: user }) }
+
+  describe '#resolve' do
+    let(:label) { create(:label, project: merge_request.project) }
+    let(:label2) { create(:label, project: merge_request.project) }
+    let(:label_ids) { [label.to_global_id] }
+    let(:mutated_merge_request) { subject[:merge_request] }
+    subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, label_ids: label_ids) }
+
+    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 update the merge request' do
+      before do
+        merge_request.project.add_developer(user)
+      end
+
+      it 'sets the labels, removing all others' do
+        merge_request.update!(labels: [label2])
+
+        expect(mutated_merge_request).to eq(merge_request)
+        expect(mutated_merge_request.labels).to contain_exactly(label)
+        expect(subject[:errors]).to be_empty
+      end
+
+      it 'returns errors merge request could not be updated' do
+        # Make the merge request invalid
+        merge_request.allow_broken = true
+        merge_request.update!(source_project: nil)
+
+        expect(subject[:errors]).not_to be_empty
+      end
+
+      context 'when passing an empty array' do
+        let(:label_ids) { [] }
+
+        it 'removes all labels' do
+          merge_request.update!(labels: [label])
+
+          expect(mutated_merge_request.labels).to be_empty
+        end
+      end
+
+      context 'when passing operation_mode as APPEND' do
+        subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, label_ids: label_ids, operation_mode: Types::MutationOperationModeEnum.enum[:append]) }
+
+        it 'sets the labels, without removing others' do
+          merge_request.update!(labels: [label2])
+
+          expect(mutated_merge_request).to eq(merge_request)
+          expect(mutated_merge_request.labels).to contain_exactly(label, label2)
+          expect(subject[:errors]).to be_empty
+        end
+      end
+
+      context 'when passing operation_mode as REMOVE' do
+        subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, label_ids: label_ids, operation_mode: Types::MutationOperationModeEnum.enum[:remove])}
+
+        it 'removes the labels, without removing others' do
+          merge_request.update!(labels: [label, label2])
+
+          expect(mutated_merge_request).to eq(merge_request)
+          expect(mutated_merge_request.labels).to contain_exactly(label2)
+          expect(subject[:errors]).to be_empty
+        end
+      end
+    end
+  end
+end

spec/graphql/types/label_type_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 
 describe GitlabSchema.types['Label'] do
   it 'has the correct fields' do
-    expected_fields = [:description, :description_html, :title, :color, :text_color]
+    expected_fields = [:id, :description, :description_html, :title, :color, :text_color]
 
     is_expected.to have_graphql_fields(*expected_fields)
   end

spec/requests/api/graphql/mutations/merge_requests/set_labels_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Setting labels of a merge request' do
+  include GraphqlHelpers
+
+  let(:current_user) { create(:user) }
+  let(:merge_request) { create(:merge_request) }
+  let(:project) { merge_request.project }
+  let(:label) { create(:label, project: project) }
+  let(:label2) { create(:label, project: project) }
+  let(:input) { { label_ids: [GitlabSchema.id_from_object(label).to_s] } }
+
+  let(:mutation) do
+    variables = {
+      project_path: project.full_path,
+      iid: merge_request.iid.to_s
+    }
+    graphql_mutation(:merge_request_set_labels, variables.merge(input),
+                     <<-QL.strip_heredoc
+                       clientMutationId
+                       errors
+                       mergeRequest {
+                         id
+                         labels {
+                           nodes {
+                             id
+                           }
+                         }
+                       }
+    QL
+    )
+  end
+
+  def mutation_response
+    graphql_mutation_response(:merge_request_set_labels)
+  end
+
+  def mutation_label_nodes
+    mutation_response['mergeRequest']['labels']['nodes']
+  end
+
+  before do
+    project.add_developer(current_user)
+  end
+
+  it 'returns an error if the user is not allowed to update the merge request' do
+    post_graphql_mutation(mutation, current_user: create(:user))
+
+    expect(graphql_errors).not_to be_empty
+  end
+
+  it 'sets the merge request labels, removing existing ones' do
+    merge_request.update(labels: [label2])
+
+    post_graphql_mutation(mutation, current_user: current_user)
+
+    expect(response).to have_gitlab_http_status(:success)
+    expect(mutation_label_nodes.count).to eq(1)
+    expect(mutation_label_nodes[0]['id']).to eq(label.to_global_id.to_s)
+  end
+
+  context 'when passing label_ids empty array as input' do
+    let(:input) { { label_ids: [] } }
+
+    it 'removes the merge request labels' do
+      merge_request.update!(labels: [label])
+
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_label_nodes.count).to eq(0)
+    end
+  end
+
+  context 'when passing operation_mode as APPEND' do
+    let(:input) { { operation_mode: Types::MutationOperationModeEnum.enum[:append], label_ids: [GitlabSchema.id_from_object(label).to_s] } }
+
+    before do
+      merge_request.update!(labels: [label2])
+    end
+
+    it 'sets the labels, without removing others' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_label_nodes.count).to eq(2)
+      expect(mutation_label_nodes).to contain_exactly({ 'id' => label.to_global_id.to_s }, { 'id' => label2.to_global_id.to_s })
+    end
+  end
+
+  context 'when passing operation_mode as REMOVE' do
+    let(:input) { { operation_mode: Types::MutationOperationModeEnum.enum[:remove], label_ids: [GitlabSchema.id_from_object(label).to_s] } }
+
+    before do
+      merge_request.update!(labels: [label, label2])
+    end
+
+    it 'removes the labels, without removing others' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_label_nodes.count).to eq(1)
+      expect(mutation_label_nodes[0]['id']).to eq(label2.to_global_id.to_s)
+    end
+  end
+end