Not a directory error on Linux in development (eager_loading issue)

[krismichalski]

I wanted to have a README.md file in rails /app directory explaining the code architecture and so on, but I found that it's causing a problem on linux machines in development. Problem does not occur on other environments that use linux or on MacOS.

I'm getting a not a directory error for app/README.md file.

Steps to reproduce

rails new test_app
cd test_app
cp README.md app/
rails s

The same steps reproduced with rails 5.2.3 give the expected behavior.
Reverting this line change also gives the expected behavior.

Expected behavior

• Rails server should start

Actual behavior

• Error: Not a directory @ dir_initialize - [test_app root]/app/README.md (Errno::ENOTDIR)
• Rails server not started

System configuration

Rails version: 6.0.0

Ruby version: 2.6.3

System: Ubuntu 18.04 / Linux Mint 19.1

Workaround

In config/application.rb:

    if Rails.env.development? && Listen::Adapter::Linux.usable?
      path_rejector = ->(path) { path.include?("app/README.md") }
      config.eager_load_paths = config.eager_load_paths.reject(&path_rejector)
    end

[fxn]

The problem here, really, is that app/README.md should not be in the autoload paths in the first place. Autoload paths should be directories, they represent Object. I suspect the code that initializes them is too permisive and not filtering out files was an overlook.

The patch that addreesed this issue processes files in ActiveSupport::Dependencies.autoload_paths and makes them watchable. However, you don't really want to watch app/README.md, don't you. Editing that file should not trigger a reload.

In Rails 7.1 the fix is going to be different. The new code iterates over Rails.autoloaders.main.dirs, which has only directories.