undefined method 'resource=' for nil:NilClass: Disabling tracing breaks grape application on 1.0.0.beta1

[ivoanjo]

Found this issue while doing a few experiments.

To reproduce, use:

1. config.ru:

require_relative 'fibonacci'

puts "prof-fibonacci started at #{Time.new.utc}"

FibClient.new.start

run FibServer

2. Gemfile:

source 'https://rubygems.org'

gem 'google-protobuf'
gem 'ddtrace', '= 1.0.0.beta1'

gem 'grape', '~> 1.6', '>= 1.6.2'
gem 'open-uri'

3. fibonacci.rb:

require 'grape'
require 'active_support/cache'
require 'ddtrace'
require 'open-uri'

Datadog.configure do |c|
  c.tracing.instrument :grape
  c.tracing.enabled = false
end

class FibServer < Grape::API
  format :json

  resource :test do
    params { requires :n, type: Integer }
    route_param :n do
      get(:test) { '' }
    end
  end
end

class FibClient
  def fib_request
    URI.open("http://127.0.0.1:18080/test/1/test")
    sleep 0.1
  end

  def wait_for_webserver
    fib_request
    puts "Web server started!"
  rescue Errno::ECONNREFUSED
    print '.'
    retry
  end

  def start
    Thread.new do
      wait_for_webserver

      puts "Workload generator started!"


      loop {
        fib_request
        print '.'
      }
    end
  end
end

And this is what happens when I run it:

$ bundle exec ddtracerb exec rackup -p 18080 -q
prof-fibonacci started at 2022-03-18 11:17:32 UTC
...................................................................[2022-03-18 11:17:32] INFO  WEBrick 1.6.1
.[2022-03-18 11:17:32] INFO  ruby 2.7.5 (2021-11-24) [x86_64-darwin19]
..........................................................................................................................................................................................................................................................................................................[2022-03-18 11:17:32] INFO  WEBrick::HTTPServer#start: pid=49243 port=18080
.E, [2022-03-18T11:17:32.862290 #49243] ERROR -- ddtrace: [ddtrace] (/Users/ivo.anjo/.rvm/gems/ruby-2.7.5/gems/ddtrace-1.0.0.beta1/lib/datadog/tracing/contrib/grape/endpoint.rb:67:in `rescue in endpoint_start_process') undefined method `resource=' for nil:NilClass
Did you mean?  rescue
Web server started!
Workload generator started!
E, [2022-03-18T11:17:32.974755 #49243] ERROR -- ddtrace: [ddtrace] (/Users/ivo.anjo/.rvm/gems/ruby-2.7.5/gems/ddtrace-1.0.0.beta1/lib/datadog/tracing/contrib/grape/endpoint.rb:67:in `rescue in endpoint_start_process') undefined method `resource=' for nil:NilClass
Did you mean?  rescue
.E, [2022-03-18T11:17:33.085210 #49243] ERROR -- ddtrace: [ddtrace] (/Users/ivo.anjo/.rvm/gems/ruby-2.7.5/gems/ddtrace-1.0.0.beta1/lib/datadog/tracing/contrib/grape/endpoint.rb:67:in `rescue in endpoint_start_process') undefined method `resource=' for nil:NilClass
Did you mean?  rescue
.E, [2022-03-18T11:17:33.191058 #49243] ERROR -- ddtrace: [ddtrace] (/Users/ivo.anjo/.rvm/gems/ruby-2.7.5/gems/ddtrace-1.0.0.beta1/lib/datadog/tracing/contrib/grape/endpoint.rb:67:in `rescue in endpoint_start_process') undefined method `resource=' for nil:NilClass

[delner]

Opened a PR to fix this: #1943.

[delner]

Opened an additional PR for Rake. While it doesn't raise an error like Grape, it does help prevent tracing from running when it shouldn't.