Support for Rails ActionableError

[connorshea]

Fixes #443, fixes #455.

This adds support for actionable exceptions in Rails. For example, when a migration needs to be run it'll offer a button that can run the migrations for the user.

Original Actionable Errors PR in Rails: rails/rails#34788

This is what the original PR uses to create the button:

<%= button_to action, ActionDispatch::ActionableExceptions.endpoint, params: {
  error: exception.class.name,
  action: action,
  location: request.path
} %>

ActionView Helpers aren't loaded in the better errors view, so I instead opted to recreate the form myself using mostly the same variables. It's not a beautiful solution, but it works and I'm not sure if there's really a better way to work around that problem.

The button looks like this:

It's hidden from the user behind the overflow, so it only shows up on hover. We could probably make it more obvious, but I'm not sure how exactly we should do it.

Reproduction steps:

• Add my fork of the better_errors gem to your Rails app. (gem 'better_errors', git: 'https://github.com/connorshea/better_errors.git', branch: 'actionable-errors')
• Run a Rails app on at least 6.0 with rails s or whatever your equivalent is for your app.
• Run rails g migration AddFooToBar in your terminal
• Load any page in your app
• See a PendingMigrationError
• See that it now has a button to run the migrations.
• Click the button.
• See the migration has now been run.

We'll also want to make sure better_errors still works on versions before Rails 6 that don't have actionable errors, and I guess add a test to better_errors for this behavior?

[ethan-dowler]

i will check this out when i have some time!

[RobinDaugherty]

Thank you @connorshea! I've made some changes to support non-Rails scenarios, I've added specs to cover the functionality, and I made some slight changes to the layout. Here's what it looks like now:

I'll merge this once as soon as the specs pass.

[connorshea]

🎉 great, thanks @RobinDaugherty!