Expose permissions on types in GraphQL

This adds a reusable way to expose permissions for a user to types in
GraphQL.

app/graphql/types/base_object.rb

 module Types
   class BaseObject < GraphQL::Schema::Object
     prepend Gitlab::Graphql::Present
+    prepend Gitlab::Graphql::ExposePermissions
     field_class Types::BaseField
   end

app/graphql/types/merge_request_type.rb

 module Types
   class MergeRequestType < BaseObject
+    expose_permissions Types::PermissionTypes::MergeRequest
+
     present_using MergeRequestPresenter
     graphql_name 'MergeRequest'

app/graphql/types/permission_types/base_permission_type.rb

+module Types
+  module PermissionTypes
+    class BasePermissionType < BaseObject
+      extend Gitlab::Allowable
+
+      RESOLVING_KEYWORDS = [:resolver, :method, :hash_key, :function].to_set.freeze
+
+      def self.abilities(*abilities)
+        abilities.each { |ability| ability_field(ability) }
+      end
+
+      def self.ability_field(ability, **kword_args)
+        unless resolving_keywords?(kword_args)
+          kword_args[:resolve] ||= -> (object, args, context) do
+            can?(context[:current_user], ability, object, args.to_h)
+          end
+        end
+
+        permission_field(ability, **kword_args)
+      end
+
+      def self.permission_field(name, **kword_args)
+        kword_args = kword_args.reverse_merge(
+          name: name,
+          type: GraphQL::BOOLEAN_TYPE,
+          description: "Whether or not a user can perform `#{name}` on this resource",
+          null: false)
+
+        field(**kword_args)
+      end
+
+      def self.resolving_keywords?(arguments)
+        RESOLVING_KEYWORDS.intersect?(arguments.keys.to_set)
+      end
+      private_class_method :resolving_keywords?
+    end
+  end
+end

app/graphql/types/permission_types/merge_request.rb

+module Types
+  module PermissionTypes
+    class MergeRequest < BasePermissionType
+      present_using MergeRequestPresenter
+      description 'Check permissions for the current user on a merge request'
+      graphql_name 'MergeRequestPermissions'
+
+      abilities :read_merge_request, :admin_merge_request,
+                :update_merge_request, :create_note
+
+      permission_field :push_to_source_branch, method: :can_push_to_source_branch?
+      permission_field :remove_source_branch, method: :can_remove_source_branch?
+      permission_field :cherry_pick_on_current_merge_request, method: :can_cherry_pick_on_current_merge_request?
+      permission_field :revert_on_current_merge_request, method: :can_revert_on_current_merge_request?
+    end
+  end
+end

app/graphql/types/permission_types/project.rb

+module Types
+  module PermissionTypes
+    class Project < BasePermissionType
+      graphql_name 'ProjectPermissions'
+
+      abilities :change_namespace, :change_visibility_level, :rename_project,
+                :remove_project, :archive_project, :remove_fork_project,
+                :remove_pages, :read_project, :create_merge_request_in,
+                :read_wiki, :read_project_member, :create_issue,  :upload_file,
+                :read_cycle_analytics, :download_code, :download_wiki_code,
+                :fork_project, :create_project_snippet, :read_commit_status,
+                :request_access, :create_pipeline, :create_pipeline_schedule,
+                :create_merge_request_from, :create_wiki, :push_code,
+                :create_deployment, :push_to_delete_protected_branch,
+                :admin_wiki, :admin_project, :update_pages,
+                :admin_remote_mirror, :create_label, :update_wiki, :destroy_wiki,
+                :create_pages, :destroy_pages
+    end
+  end
+end

app/graphql/types/project_type.rb

 module Types
   class ProjectType < BaseObject
+    expose_permissions Types::PermissionTypes::Project
+
     graphql_name 'Project'
     field :id, GraphQL::ID_TYPE, null: false

app/presenters/merge_request_presenter.rb

@@ -168,6 +168,10 @@ class MergeRequestPresenter < Gitlab::View::Presenter::Delegated
       .can_push_to_branch?(source_branch)
   end
+  def can_remove_source_branch?
+    source_branch_exists? && merge_request.can_remove_source_branch?(current_user)
+  end
+
   def mergeable_discussions_state
     # This avoids calling MergeRequest#mergeable_discussions_state without
     # considering the state of the MR first. If a MR isn't mergeable, we can

app/serializers/merge_request_widget_entity.rb

@@ -109,7 +109,7 @@ class MergeRequestWidgetEntity < IssuableEntity
   expose :current_user do
     expose :can_remove_source_branch do |merge_request|
-      merge_request.source_branch_exists? && merge_request.can_remove_source_branch?(current_user)
+      presenter(merge_request).can_remove_source_branch?
     end
     expose :can_revert_on_current_merge_request do |merge_request|

changelogs/unreleased/bvl-graphql-permissions.yml

+---
+title: 'Expose permissions of the current user on resources in GraphQL'
+merge_request: 20152
+author:
+type: added

doc/api/graphql/index.md

-# GraphQL API (Beta)
+# GraphQL API (Alpha)
 > [Introduced][ce-19008] in GitLab 11.0.

doc/development/api_graphql_styleguide.md

@@ -54,6 +54,51 @@ a new presenter specifically for GraphQL.
 The presenter is initialized using the object resolved by a field, and
 the context.
+### Exposing permissions for a type
+
+To expose permissions the current user has on a resource, you can call
+the `expose_permissions` passing in a separate type representing the
+permissions for the resource.
+
+For example:
+
+```ruby
+module Types
+  class MergeRequestType < BaseObject
+    expose_permissions Types::MergeRequestPermissionsType
+  end
+end
+```
+
+The permission type inherits from `BasePermissionType` which includes
+some helper methods, that allow exposing permissions as non-nullable
+booleans:
+
+```ruby
+class MergeRequestPermissionsType < BasePermissionType
+  present_using MergeRequestPresenter
+
+  graphql_name 'MergeRequestPermissions'
+
+  abilities :admin_merge_request, :update_merge_request, :create_note
+
+  ability_field :resolve_note,
+                description: 'Whether or not the user can resolve disussions on the merge request'
+  permission_field :push_to_source_branch, method: :can_push_to_source_branch?
+end
+```
+
+- **`permission_field`**: Will act the same as `graphql-ruby`'s
+  `field` method but setting a default description and type and making
+  them non-nullable. These options can still be overridden by adding
+  them as arguments.
+- **`ability_field`**: Expose an ability defined in our policies. This
+  takes behaves the same way as `permission_field` and the same
+  arguments can be overridden.
+- **`abilities`**: Allows exposing several abilities defined in our
+  policies at once. The fields for these will all have be non-nullable
+  booleans with a default description.
+
 ## Resolvers
 To find objects to display in a field, we can add resolvers to

lib/gitlab/graphql/expose_permissions.rb

+module Gitlab
+  module Graphql
+    module ExposePermissions
+      extend ActiveSupport::Concern
+      prepended do
+        def self.expose_permissions(permission_type, description: 'Permissions for the current user on the resource')
+          field :user_permissions, permission_type,
+                description: description,
+                null: false,
+                resolve: -> (obj, _, _) { obj }
+        end
+      end
+    end
+  end
+end

lib/gitlab/graphql/present/instrumentation.rb

@@ -10,9 +10,18 @@ module Gitlab
           old_resolver = field.resolve_proc
           resolve_with_presenter = -> (presented_type, args, context) do
+            # We need to wrap the original presentation type into a type that
+            # uses the presenter as an object.
             object = presented_type.object
+
+            if object.is_a?(presented_in.presenter_class)
+              next old_resolver.call(presented_type, args, context)
+            end
+
             presenter = presented_in.presenter_class.new(object, **context.to_h)
-            old_resolver.call(presenter, args, context)
+            wrapped = presented_type.class.new(presenter, context)
+
+            old_resolver.call(wrapped, args, context)
           end
           field.redefine do

spec/graphql/types/merge_request_type_spec.rb

+require 'spec_helper'
+
+describe Types::MergeRequestType do
+  it { expect(described_class).to expose_permissions_using(Types::PermissionTypes::MergeRequest) }
+end

spec/graphql/types/permission_types/base_permission_type_spec.rb

+require 'spec_helper'
+
+describe Types::PermissionTypes::BasePermissionType do
+  let(:permitable) { double('permittable') }
+  let(:current_user) { build(:user) }
+  let(:context) { { current_user: current_user } }
+  subject(:test_type) do
+    Class.new(described_class) do
+      graphql_name 'TestClass'
+
+      permission_field :do_stuff, resolve: -> (_, _, _)  { true }
+      ability_field(:read_issue)
+      abilities :admin_issue
+    end
+  end
+
+  describe '.permission_field' do
+    it 'adds a field for the required permission' do
+      is_expected.to have_graphql_field(:do_stuff)
+    end
+  end
+
+  describe '.ability_field' do
+    it 'adds a field for the required permission' do
+      is_expected.to have_graphql_field(:read_issue)
+    end
+
+    it 'does not add a resolver block if another resolving param is passed' do
+      expected_keywords = {
+        name: :resolve_using_hash,
+        hash_key: :the_key,
+        type: GraphQL::BOOLEAN_TYPE,
+        description: "custom description",
+        null: false
+      }
+      expect(test_type).to receive(:field).with(expected_keywords)
+
+      test_type.ability_field :resolve_using_hash, hash_key: :the_key, description: "custom description"
+    end
+  end
+
+  describe '.abilities' do
+    it 'adds a field for the passed permissions' do
+      is_expected.to have_graphql_field(:admin_issue)
+    end
+  end
+end

spec/graphql/types/permission_types/merge_request_spec.rb

+require 'spec_helper'
+
+describe Types::PermissionTypes::MergeRequest do
+  it do
+    expected_permissions = [
+      :read_merge_request, :admin_merge_request, :update_merge_request,
+      :create_note, :push_to_source_branch, :remove_source_branch,
+      :cherry_pick_on_current_merge_request, :revert_on_current_merge_request
+    ]
+
+    expect(described_class).to have_graphql_fields(expected_permissions)
+  end
+end

spec/graphql/types/permission_types/merge_request_type_spec.rb

+require 'spec_helper'
+
+describe Types::MergeRequestType do
+  it { expect(described_class).to expose_permissions_using(Types::PermissionTypes::MergeRequest) }
+end

spec/graphql/types/permission_types/project_spec.rb

+require 'spec_helper'
+
+describe Types::PermissionTypes::Project do
+  it do
+    expected_permissions = [
+      :change_namespace, :change_visibility_level, :rename_project, :remove_project, :archive_project,
+      :remove_fork_project, :remove_pages, :read_project, :create_merge_request_in,
+      :read_wiki, :read_project_member, :create_issue,  :upload_file, :read_cycle_analytics,
+      :download_code, :download_wiki_code, :fork_project, :create_project_snippet,
+      :read_commit_status, :request_access, :create_pipeline, :create_pipeline_schedule,
+      :create_merge_request_from, :create_wiki, :push_code, :create_deployment, :push_to_delete_protected_branch,
+      :admin_wiki, :admin_project, :update_pages, :admin_remote_mirror, :create_label,
+      :update_wiki, :destroy_wiki, :create_pages, :destroy_pages
+    ]
+
+    expect(described_class).to have_graphql_fields(expected_permissions)
+  end
+end

spec/graphql/types/project_type_spec.rb

 require 'spec_helper'
 describe GitlabSchema.types['Project'] do
+  it { expect(described_class).to expose_permissions_using(Types::PermissionTypes::Project) }
+
   it { expect(described_class.graphql_name).to eq('Project') }
   describe 'nested merge request' do

spec/requests/api/graphql/project/merge_request_spec.rb

+require 'spec_helper'
+
+describe 'getting merge request information nested in a project' do
+  include GraphqlHelpers
+
+  let(:project) { create(:project, :repository, :public) }
+  let(:current_user) { create(:user) }
+  let(:merge_request_graphql_data) { graphql_data['project']['mergeRequest'] }
+  let!(:merge_request) { create(:merge_request, source_project: project) }
+
+  let(:query) do
+    graphql_query_for(
+      'project',
+      { 'fullPath' => project.full_path },
+      query_graphql_field('mergeRequest', iid: merge_request.iid)
+    )
+  end
+
+  it_behaves_like 'a working graphql query' do
+    before do
+      post_graphql(query, current_user: current_user)
+    end
+  end
+
+  it 'contains merge request information' do
+    post_graphql(query, current_user: current_user)
+
+    expect(merge_request_graphql_data).not_to be_nil
+  end
+
+  # This is a field coming from the `MergeRequestPresenter`
+  it 'includes a web_url' do
+    post_graphql(query, current_user: current_user)
+
+    expect(merge_request_graphql_data['webUrl']).to be_present
+  end
+
+  context 'permissions on the merge request' do
+    it 'includes the permissions for the current user on a public project' do
+      expected_permissions = {
+        'readMergeRequest' => true,
+        'adminMergeRequest' => false,
+        'createNote' => true,
+        'pushToSourceBranch' => false,
+        'removeSourceBranch' => false,
+        'cherryPickOnCurrentMergeRequest' => false,
+        'revertOnCurrentMergeRequest' => false,
+        'updateMergeRequest' => false
+      }
+      post_graphql(query, current_user: current_user)
+
+      permission_data = merge_request_graphql_data['userPermissions']
+
+      expect(permission_data).to be_present
+      expect(permission_data).to eq(expected_permissions)
+    end
+  end
+
+  context 'when the user does not have access to the merge request' do
+    let(:project) { create(:project, :public, :repository) }
+
+    it 'returns nil' do
+      project.project_feature.update!(merge_requests_access_level: ProjectFeature::PRIVATE)
+
+      post_graphql(query)
+
+      expect(merge_request_graphql_data).to be_nil
+    end
+  end
+end