GraphQL::Tracing::ActiveSupportNotificationsTrace raises a NoMethodError in v2.5.0

[yn-misaki]

When using GraphQL Ruby 2.5.0 with both GraphQL::Tracing::ActiveSupportNotificationsTrace and GraphQL::Dataloader, an intermittent NoMethodError exception occasionally occurs during query execution.

workspace/graphql-ruby/lib/graphql/tracing/notifications_trace.rb:142:in 'GraphQL::Tracing::NotificationsTrace#dataloader_fiber_resume': undefined method 'name' for nil (NoMethodError)

        begin_notifications_event(prev_ev.name, prev_ev.payload)

Versions

graphql version: 2.5.0
rails (or other framework): 8.0.2

GraphQL schema and query

require 'bundler/inline'

gemfile do
  gem 'graphql', path: "./"
  gem 'sqlite3'
  gem 'activerecord', require: 'active_record'
end

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Schema.define do
  create_table :microposts do |t|
    t.string(:content)
    t.belongs_to :user
  end
  create_table :users do |t|
    t.string(:name)
  end
end

class Micropost < ActiveRecord::Base; end

class User < ActiveRecord::Base
  has_many :microposts
end

user = User.create!(name: 'Sample')
user.microposts.create!(content: 'Hello World!')

class MySchema < GraphQL::Schema
  class Micropost < GraphQL::Schema::Object
    field :content, String
  end

  class User < GraphQL::Schema::Object
    field :name, String
    field :microposts, [Micropost]
  end

  class Query < GraphQL::Schema::Object
    field :microposts, [Micropost] do
      argument :user_id, ID, loads: User
    end

    def microposts(user:)
      user.microposts
    end
  end

  max_complexity 1000
  query(Query)
  trace_with(GraphQL::Tracing::ActiveSupportNotificationsTrace)
  use(GraphQL::Dataloader)

  def self.object_from_id(id, ctx)
    ctx.dataloader.with(GraphQL::Dataloader::ActiveRecordSource, ::User).load(id)
  end

  def self.resolve_type(abs_t, obj, ctx)
    User
  end
end

query_str = <<~GRAPHQL
  query queryOne($userId: ID!) {
    microposts(userId: $userId) {
      content
    }
  }
GRAPHQL

query = GraphQL::Query.new(MySchema, query_str, variables: { userId: '1' })
pp query.result.to_h

Actual behavior

Click to view exception backtrace

workspace/graphql-ruby/lib/graphql/tracing/notifications_trace.rb:142:in 'GraphQL::Tracing::NotificationsTrace#dataloader_fiber_resume': undefined method 'name' for nil (NoMethodError)

        begin_notifications_event(prev_ev.name, prev_ev.payload)
                                         ^^^^^
        from workspace/graphql-ruby/lib/graphql/dataloader.rb:138:in 'GraphQL::Dataloader#yield'
        from workspace/graphql-ruby/lib/graphql/dataloader/source.rb:96:in 'GraphQL::Dataloader::Source#sync'
        from workspace/graphql-ruby/lib/graphql/dataloader/source.rb:57:in 'GraphQL::Dataloader::Source#load'
        from workspace/graphql-ruby/lib/graphql/dataloader/active_record_source.rb:15:in 'GraphQL::Dataloader::ActiveRecordSource#load'
        from dataloder_sample.rb:60:in 'MySchema.object_from_id'
        from workspace/graphql-ruby/lib/graphql/schema/member/has_arguments.rb:335:in 'GraphQL::Schema::Member::HasArguments::ArgumentObjectLoader#object_from_id'
        from workspace/graphql-ruby/lib/graphql/schema/member/has_arguments.rb:343:in 'GraphQL::Schema::Member::HasArguments::ArgumentObjectLoader#load_application_object'
        from workspace/graphql-ruby/lib/graphql/schema/member/has_arguments.rb:347:in 'GraphQL::Schema::Member::HasArguments::ArgumentObjectLoader#load_and_authorize_application_object'
        from workspace/graphql-ruby/lib/graphql/schema/argument.rb:356:in 'GraphQL::Schema::Argument#load_and_authorize_value'
        from workspace/graphql-ruby/lib/graphql/schema/argument.rb:292:in 'block in GraphQL::Schema::Argument#coerce_into_values'
        from workspace/graphql-ruby/lib/graphql/execution/interpreter/runtime.rb:784:in 'GraphQL::Execution::Interpreter::Runtime#minimal_after_lazy'
        from workspace/graphql-ruby/lib/graphql/query.rb:414:in 'GraphQL::Query#after_lazy'
        from workspace/graphql-ruby/lib/graphql/schema/argument.rb:282:in 'GraphQL::Schema::Argument#coerce_into_values'
        from workspace/graphql-ruby/lib/graphql/schema/member/has_arguments.rb:255:in 'block (3 levels) in GraphQL::Schema::Member::HasArguments#coerce_arguments'
        from workspace/graphql-ruby/lib/graphql/dataloader.rb:300:in 'block in GraphQL::Dataloader#spawn_job_fiber'
        from workspace/graphql-ruby/lib/graphql/dataloader.rb:255:in 'block in GraphQL::Dataloader#spawn_fiber'

Additional context

This issue is caused by changes introduced in PR #5298. The error can be fixed by modifying the code similar to how it's implemented in lib/graphql/tracing/monitor_trace.rb, by adding a nil check:

def dataloader_fiber_resume(source)
  prev_ev = Fiber[PREVIOUS_EV_KEY]
  if prev_ev
    begin_notifications_event(prev_ev.name, prev_ev.payload)
  end
  super
end

Since the exact conditions that trigger this error are not clearly understood, it's difficult to write a reliable test case.
I would like your support, if possible.

[rmosolgo]

Thanks for the detailed report, and sorry for the trouble! I've worked up a fix over at #5335

[yn-misaki]

Thank you very much for your quick response. I now understand how to write the test code for the PR.