Remove prepended forward slash when mapping.path is empty

[jsntv200]

While using ViewComponents I ran into an issue with sidecar loaded js files not being mapped correctly when using importmap-rails and propshaft. The issue has been raised in Propshaft Issue #87 and ViewComponents Issue #1064 neither of which provided solutions I wanted to use.

Digging into it I found that using the following config nearly produced the desired output:

# config/initializers/assets.rb

Rails.application.config.assets.paths << "app/components"

# config/importmap.rb

pin_all_from "app/components", under: "controllers", to: ""

# bin/importmap json

{
  "imports": {
    "controllers/button/component_controller": "/button/component_controller.js"
  }
}

I assume Propshaft interprets the path as absolute and fails to digest it.

This fix just adds reject(&:empty?) to remove empty strings allowing mapping.path to essentially overwrite mapping.under allowing the path to be resolved by Propshaft.

After fix:

# bin/importmap json

{
  "imports": {
    "controllers/button/component_controller": "/assets/button/component_controller-c4927eee0e86a379df3997e9f426970d37d60dc2.js"
  }
}

The test covers the ViewComponent scenario of a directory located at app/components which is the reason for passing to: "" in the first place.

If there's a legitimate reason for requiring the forward slash then I assume to: "/" would still work.