Improve the condition of webpacker major version

[6br]

Summary

I found server-side rendering failed in our environment Rails 5.2, webpacker 4.0.0.pre.pre.2, webpack 4.4.1. The error message is following.

Failure/Error: <%= react_component("SearchFilter", {}, {prerender: true}) %>

     ActionView::Template::Error:
       No such file or directory @ rb_sysopen - public/server_rendering-0c232d693da2fd422ba9.js
     # ./app/views/users/_filter.html.erb:2:in `_app_views_recipes__filter_html_erb___2340570384952592713_70205888111860'
     # ./app/views/users/index.html.erb:6:in `_app_views_users_index_html_erb___4199468956611823080_70205888379400'
     # ------------------

The path public/server_rendering-0c232d693da2fd422ba9.js is not proper because my webpacker.yaml is following. public/packs/server_rendering-0c232d693da2fd422ba9.js is correct.

default: &default
  source_path: app/javascript
  source_entry_path: packs
  public_output_path: packs
  cache_path: tmp/cache/webpacker

Since it depends on the version of webpacker, I mofidied lib/react/server_rendering/webpacker_manifest_container.rb.

[BookOfGreg]

Good catch, thank you for the fix!

[ttanimichi]

📝 We probably don’t have to add test cases to https://github.com/reactjs/react-rails/blob/a91e0d84a5ce3d0aafe56d1d9410a533efafd272/test/react/server_rendering/webpacker_manifest_container_test.rb . But, it seems that we need to do some more work to support webpacker v4. e.g. Add gemfiles which contains it.

[ttanimichi]

@6br Nice catch. Thanks! ✨

[ttanimichi]

Pushed 467cbd8 which is related to this PR.