Unable to parse queries when using Graphql::Backtrace

[alksl]

In graphql-ruby version 1.12.2 I can no longer parse queries when using Graphql::Backtrace. It seem to be a regression from when the multiplex batch loading was added #3264

I'm getting this error message when using Client.parse:

Traceback (most recent call last):
	5: from test.rb:60:in `<main>'
	4: from /home/anton/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/graphql-client-0.16.0/lib/graphql/client.rb:194:in `parse'
	3: from /home/anton/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/graphql-1.12.3/lib/graphql/static_validation/validator.rb:29:in `validate'
	2: from /home/anton/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/graphql-1.12.3/lib/graphql/tracing.rb:67:in `trace'
	1: from /home/anton/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/graphql-1.12.3/lib/graphql/tracing.rb:83:in `call_tracers'
/home/anton/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/graphql-1.12.3/lib/graphql/backtrace/tracer.rb:51:in `trace': undefined method `context' for nil:NilClass (NoMethodError)

The nil value is generated from query.multiplex in the backtrace tracer on line 21 and is later used on line 51

This code should be sufficent to reproduce the issue.

gem 'graphql', '= 1.12.3'
gem 'graphql-client', '= 0.16.0'

require 'graphql'
require 'graphql/client'

class LocalExecution
  def initialize(schema)
    @schema = schema
  end

  def execute(
    document:,
    operation_name: nil,
    variables: {},
    context: {}
  )
    GraphQL::Query.new(
      @schema,
      document.to_query_string,
      variables: variables,
      context: validate_context(context),
      operation_name: operation_name
    ).result
  end

  protected

  def validate_context(context)
    context
  end
end

class TestType < GraphQL::Schema::Object
  graphql_name 'Test'

  field :test_field, String, null: false

  def test_field
    'Test test'
  end
end

class QueryRoot < GraphQL::Schema::Object
  graphql_name 'Query'

  field :test, TestType, null: false
end

class Schema < GraphQL::Schema
  query QueryRoot
  use GraphQL::Backtrace # Works without GraphQL::Backtrace
end

Client = GraphQL::Client.new(
  schema: Schema,
  execute: LocalExecution.new(Schema)
)

Client.parse <<~GRAPHQL
  query {
    test {
      testField
    }
  }
GRAPHQL

[rmosolgo]

Thanks for reporting this! It looks like this check:

graphql-ruby/lib/graphql/backtrace/tracer.rb

Lines 50 to 53 in 6b17312

	if push_data
	multiplex.context[:graphql_backtrace_contexts][push_key] = push_data
	multiplex.context[:last_graphql_backtrace_context] = push_data
	end

Should be expanded to if push_data && multiplex