FrozenError: can't modify frozen Array when adding devServer middleware

[mikker]

I have no idea why but somehow, in one of my projects, app.middleware.middlewares is frozen when Webpacker tries to insert its devServer middleware.

I've "fixed" it by duping the array (see master...mikker:frozen-middlewares).

I've tried disable some gems and the like but haven't been able to find the culprit yet.

---

Ruby: 2.5.1
Rails: 5.2.1
Webpacker: 3.5.5 and/or master

[gauravtiwari]

Hey @mikker

Are you eager loading code in development?

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

[mikker]

Nope, config.eager_load = false

[rossta]

@mikker Any chance you're using ActiveAdmin ~> 1.4.1? I've seen similar issues reported elsewhere with that being another common link. That release does some introspection in the app middleware that could be a root cause, though I wasn't able to reproduce the issue myself.

• action_dispatch/middleware/stack.rb: can't modify frozen Array rails#33745
• "can't modify frozen Array" error during generation railsadminteam/rails_admin#3060
• If this gem is present in Gemfile and installed, an error is thrown at each rails invocation rossta/serviceworker-rails#59

[vincentwoo]

I'm also seeing this with RailsAdmin 1.4.1 but not 1.4.0. It seems likely this commit (railsadminteam/rails_admin@59478af) is responsible, but I can't for the life of me figure out why.

[mshibuya]

Sorry to bother you, RailsAdmin 1.4.2 is out with the fix for this:
railsadminteam/rails_admin@94928d1

[vincentwoo]

Thanks, appreciate the update!

[marcelino056]

Still having the same issue:

Completed 500 Internal Server Error in 3765ms (ActiveRecord: 278.3ms)
  
FrozenError (can't modify frozen fatal):

rails_admin (1.4.2)
ruby 2.5.5
rails 5.2.2