Webpacker: Deploying to "staging" environment required manually setting `public_root_path: public`

[Casey1449]

Using 4.0.0.rc.2, but didn't notice any relevant changes in the CHANGELOG since that version. So I apologize in advance if I missed it, or if this was user error.

Deploying with nginx and puma, using RAILS_ENV=staging, we experience the following error trace (thrown from puma):

Error during failsafe response: no implicit conversion of nil into String
  ...rbenv/versions/2.5.1/lib/ruby/2.5.0/pathname.rb:411:in `initialize'
  ...rbenv/versions/2.5.1/lib/ruby/2.5.0/pathname.rb:411:in `new'
  ...rbenv/versions/2.5.1/lib/ruby/2.5.0/pathname.rb:411:in `join'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/configuration.rb:39:in `public_path'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/configuration.rb:43:in `public_output_path'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/configuration.rb:47:in `public_manifest_path'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/manifest.rb:84:in `load'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/manifest.rb:64:in `data'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/manifest.rb:71:in `find'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/manifest.rb:40:in `lookup'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/manifest.rb:50:in `lookup!'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/helper.rb:93:in `block in sources_from_pack_manifest'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/helper.rb:93:in `map'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/helper.rb:93:in `sources_from_pack_manifest'
  .../.../shared/vendor/bundle/ruby/2.5.0/bundler/gems/webpacker-c8375ded9bc8/lib/webpacker/helper.rb:83:in `stylesheet_pack_tag'

It looked like maybe pathname was choking on this line, being given a nil :public_root_path: https://github.com/rails/webpacker/blob/master/lib/webpacker/configuration.rb#L39

Sure enough, when I added a root path to my webpacker.yml:
public_root_path: public
...it worked and deployed smoothly, even though public is ostensibly the default path.

Here's my config before manually adding public as the root path. (Skimpy, because we're using a set of traditional webpack config files behind webpacker):

default: &default
  source_path: client
  source_entry_path: app/application
  public_output_path: packs
  cache_path: tmp/cache/webpacker
  cache_manifest: false
  compile: false
  check_yarn_integrity: false
  extract_css: true

development:
  <<: *default

  extract_css: false

test:
  <<: *default

  public_output_path: packs-test

staging:
  <<: *default

  cache_manifest: true

production:
  <<: *default

  cache_manifest: true

Our setup works fine when RAILS_ENV=development, regardless of whether I'm using HMR, watching a static dev build, or using prod-mode webpack bundles (minified, gzipped, etc).

Questions/Issues:

1. Are default root paths missing? Or maybe missing for custom rails environments?
2. Or, if there is no bug, why did I have to set one in my case, to what I thought was the default anyway?

[xxx]

We ran into this upgrading from rc.2 to rc.7. Setting public_root_path explicitly resolved it for us.

[johnstoecker]

I can confirm that this works, specifically adding:

default: &default
  public_root_path: public
  ...

to webpacker.yml

[HendrikPetertje]

Thanks folks, fixed the problems for us as well.
We are in the process of walking away from having special snow-flake envs like "staging" and just run those envs in production so we replicate exact the same behaviour between our production and stage-test apps, but until that this should fix it for us too.

On that subject and Rails being mostly "Convention over configuration" - is it possible to make public_root_path: public the standard option in new and existing rails apps? or is there a strong argument that I miss here, that specifies why we would need to set this variable explicitly?

[abeger]

This is still an issue in 4.0.7. Thank goodness for this ticket--I was tearing my hair out

[rossta]

For anyone else upgrading from v3 to v4, please be sure to review the upgrade guide carefully. One of the items includes tending to differences in config/webpacker.yml.

[guillaumebriday]

Could this issue be closed?