Rails 3.x launcher script was found instead of Rails 4.x one.

Upgrading to Rails 4 in an existing application can be quite a switch. I decided to make the jump and handle any complications as they come. After about an hour or so I was mostly up and running, with a few issues here and there with gems I am using and their various versions.

Resources

As is often the case, the Railscast on the subject proved invaluable. There is also a robust compilation of Rails 4 links being maintainedhere.

RubyMine

If you use RubyMine, you may run across an error when trying to start your development server.

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Error running Development: Rails 3.x launcher script was found instead of Rails 4.x one.

When a new Rails 4 application is created, it generates a ‘bin’ folder. Creating a new, blank Rails 4 application and copying its ‘bin’ folder into the existing project will resolve the error and allow the server to be started in RubyMine.

Gems

One gem that gave me a few errors was simple form. I updated my Gemfile to:

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gem 'simple_form', '~> 3.0.0.rc'

However, when loading my forms in the browser, I received another error:

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wrong number of arguments (3 for 2)

After doing some digging I found that this was actually related to the client_side_validations gem, which I was no longer using and safely removed this from the project. If you need this gem, there is abranch for Rails 4 which should help.

Looking forward to implementing the great additions in Rails 4.