Consider creating error base class in bundler gem

[christhekeele]

Ruby 2 updated the docs for Exception from:

Programs may subclass Exception, or more typically StandardError to provide custom classes and add additional information.

to instead read:

It is recommended that a library should have one subclass of StandardError or RuntimeError and have specific exception types inherit from it. This allows the user to rescue a generic exception type to catch all exceptions the library may raise even if future versions of the library add new exception subclasses.

For example:

class MyLibrary
  class Error < RuntimeError
  end

  class WidgetError < Error
  end

  class FrobError < Error
  end

end

To handle both WidgetError and FrobError the library user can rescue MyLibrary::Error.

This is awesome, and important.

---

I'd like to propose adding a default error base class to the bundle gem scaffolding to encourage this good pattern. This could be as simple as bundle gem foo producing:

  # foo/lib/foo.rb
  require "foo/version"

  module Foo
+   class Error < StandardError; end
    # Your code goes here...
  end

It is nearly as effortless to delete both that line and the comment line as the comment line itself; but plants the seed for a very important and often-overlooked best practice early in a gem's development.

---

If well received I think we could discuss whether or not to add more context/comments to it than just the one-liner class; as well as minutiae like if the ; end is good form. Initially just gonna pitch the general concept, though, I don't want to get too caught up in those other more focused discussions immediately.

[colby-swandale]

A PR for this would be very appreciated 👍