Rails 5.1: "unknown firstpos: NilClass" - Issue reloading application

Question

Following an upgrade from Rails 5.0 to 5.1 I'm getting this error anytime the app reloads, either from code changes during rails server or if I call reload! from the console.

🌶 13:53$ rc
Loading development environment (Rails 5.1.1)
2.3.1 :001 > reload!
Reloading...
ArgumentError: unknown firstpos: NilClass
    from (irb):1
2.3.1 :002 > 

https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/journey/gtg/builder.rb

Application Trace is empty, here's the Framework Trace:

actionpack (5.1.1) lib/action_dispatch/journey/gtg/builder.rb:99:in `firstpos'
actionpack (5.1.1) lib/action_dispatch/journey/gtg/builder.rb:22:in `transition_table'
actionpack (5.1.1) lib/action_dispatch/journey/routes.rb:58:in `simulator'
actionpack (5.1.1) lib/action_dispatch/journey/router.rb:92:in `simulator'
actionpack (5.1.1) lib/action_dispatch/journey/router.rb:28:in `eager_load!'
actionpack (5.1.1) lib/action_dispatch/routing/route_set.rb:382:in `eager_load!'
railties (5.1.1) lib/rails/application/routes_reloader.rb:26:in `each'
railties (5.1.1) lib/rails/application/routes_reloader.rb:26:in `execute'
railties (5.1.1) lib/rails/application/finisher.rb:141:in `block (2 levels) in <module:Finisher>'
activesupport (5.1.1) lib/active_support/callbacks.rb:413:in `instance_exec'
activesupport (5.1.1) lib/active_support/callbacks.rb:413:in `block in make_lambda'
activesupport (5.1.1) lib/active_support/callbacks.rb:197:in `block (2 levels) in halting'
activesupport (5.1.1) lib/active_support/callbacks.rb:601:in `block (2 levels) in default_terminator'
activesupport (5.1.1) lib/active_support/callbacks.rb:600:in `catch'
activesupport (5.1.1) lib/active_support/callbacks.rb:600:in `block in default_terminator'
activesupport (5.1.1) lib/active_support/callbacks.rb:198:in `block in halting'
activesupport (5.1.1) lib/active_support/callbacks.rb:507:in `block in invoke_before'
activesupport (5.1.1) lib/active_support/callbacks.rb:507:in `each'
activesupport (5.1.1) lib/active_support/callbacks.rb:507:in `invoke_before'
activesupport (5.1.1) lib/active_support/callbacks.rb:130:in `run_callbacks'
activesupport (5.1.1) lib/active_support/execution_wrapper.rb:108:in `run!'
activesupport (5.1.1) lib/active_support/reloader.rb:113:in `run!'
activesupport (5.1.1) lib/active_support/execution_wrapper.rb:70:in `block in run!'
activesupport (5.1.1) lib/active_support/execution_wrapper.rb:67:in `tap'
activesupport (5.1.1) lib/active_support/execution_wrapper.rb:67:in `run!'
activesupport (5.1.1) lib/active_support/reloader.rb:59:in `run!'
actionpack (5.1.1) lib/action_dispatch/middleware/executor.rb:10:in `call'
actionpack (5.1.1) lib/action_dispatch/middleware/debug_exceptions.rb:59:in `call'
actionpack (5.1.1) lib/action_dispatch/middleware/show_exceptions.rb:31:in `call'
railties (5.1.1) lib/rails/rack/logger.rb:36:in `call_app'
railties (5.1.1) lib/rails/rack/logger.rb:24:in `block in call'
activesupport (5.1.1) lib/active_support/tagged_logging.rb:69:in `block in tagged'
activesupport (5.1.1) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (5.1.1) lib/active_support/tagged_logging.rb:69:in `tagged'
railties (5.1.1) lib/rails/rack/logger.rb:24:in `call'
sprockets-rails (3.2.0) lib/sprockets/rails/quiet_assets.rb:13:in `call'
actionpack (5.1.1) lib/action_dispatch/middleware/remote_ip.rb:79:in `call'
request_store (1.3.2) lib/request_store/middleware.rb:9:in `call'
actionpack (5.1.1) lib/action_dispatch/middleware/request_id.rb:25:in `call'
rack (2.0.3) lib/rack/method_override.rb:22:in `call'
rack (2.0.3) lib/rack/runtime.rb:22:in `call'
activesupport (5.1.1) lib/active_support/cache/strategy/local_cache_middleware.rb:27:in `call'
actionpack (5.1.1) lib/action_dispatch/middleware/executor.rb:12:in `call'
actionpack (5.1.1) lib/action_dispatch/middleware/static.rb:125:in `call'
rack (2.0.3) lib/rack/sendfile.rb:111:in `call'
railties (5.1.1) lib/rails/engine.rb:522:in `call'
puma (3.9.1) lib/puma/configuration.rb:224:in `call'
puma (3.9.1) lib/puma/server.rb:602:in `handle_request'
puma (3.9.1) lib/puma/server.rb:435:in `process_client'
puma (3.9.1) lib/puma/server.rb:299:in `block in run'
puma (3.9.1) lib/puma/thread_pool.rb:120:in `block in spawn_thread'

Beulahbeuthel

can you try this link collectiveidea.com/blog/archives/2016/07/22/… – Lib

Answer 1

Workaround found! https://github.com/rails/rails/pull/32296

The pull request is not merged, and will probably only be in 5.2+ anyway. Adding a monkey patch with the one-line change fixed the problem entirely for me.

config/initializers/routes.rb

# MONKEY PATCH!!!
# https://github.com/rails/rails/pull/32296
#
# Fixes:
# * Development mode deadlocks
# * ArgumentError: unknown firstpos: NilClass
#
# Allows use of "config.eager_load = true"


module ActionDispatch
  module Journey
    class Routes
      def simulator
        @simulator ||= begin
          gtg = GTG::Builder.new(ast).transition_table unless ast.blank?
          GTG::Simulator.new(gtg)
        end
      end
    end
  end
end

Beulahbeuthel

For the record: 32296 was closed in favor of github.com/rails/rails/pull/33118 and the bug is confirmed to still exist in 5.2.0 – Rhodium

This was the only thing that worked for me. I wrapped mine with github.com/ingoweiss/gem-patching (old gem, still works) Gem.patching("rails", "5.2.0") do...end so I won't forget to remove it – Median

Problem still there with 5.2.1 – Merralee

Answer 2

I just faced exactly the same problem. I sovled it by setting:

config/environments/development.rb

from:

# Do not eager load code on boot.
config.eager_load = true

to:

**# Do not eager load code on boot.
config.eager_load = false

Hope this helps! Cheers, Nic.

Serigraph

I prefer to use eager_load on dev boot as a sort of static code analyzer. If you have a syntax error anywhere you know about it immediately. That said, I tried it anyway and unfortunately it didn't have any effect. I also tried building a new rails 5.1.1 app and both ways worked as expected, with and without spring... humm – Beulahbeuthel

worked for me, but there still must be another way to do it (or why would there be this option anyway from 5.1 on) – Draw

It seems very undesirable to disable a key feature of Rails just to get around this problem, let alone a feature that may be necessary for some. – Buhr

Answer 3

Seems it is Spring hanging or something. Just run spring stop and it should go away. Alternatively you can start the rails console without spring like this:

DISABLE_SPRING=true rails c.

Draw

I don't run Spring, we ran into problems with it when it was introduced and never bothered with it since. For now I've just postponed my 5.1 upgrade. 5.0 is working great. – Beulahbeuthel

Doesn't help for me – Gyrostat

Answer 4

I started having this problem after upgrading Rails from 5.1 to 5.2
It got solved by:

spring stop
spring binstub --all
spring start
rails s

Ligule

This actually worked for me! No monkey patch needed, thanks man! Will have to see if it lasts but if it does it's great :) – Idiocy

This certainly modified my binstubs for spring, rake, rspec, rails but it didn't make the bug go away – Median

Answer 5

You will not get this bug in production environment and in a test environment (if you don't use Spring). Because this bug "ArgumentError: unknown firstpos: NilClass" you got in "reload" when it tried to reload some your classes.

In production and test environments all things are in cache, so all your things will be cached and bug will not happen

Unfortunately (for now) for the development environment, I also found only this solution

config.eager_load = false

Higgs