Ensure Concurrency Keys are string-like and return a better error when they cannot be cast to a string

[Earlopain]

Closes #784

If you pass something like a Hash or Array as the concurrency key, the resulting stack trace doesn't make it very clear what you did wrong:

   TypeError:
     can't cast Hash
   # ./app/models/good_job/lockable.rb:196:in `advisory_lock_key'
   # ./lib/good_job/active_job_extensions/concurrency.rb:51:in `block (2 levels) in <module:Concurrency>'
   # ./spec/lib/good_job/active_job_extensions/concurrency_spec.rb:157:in `block (4 levels) in <top (required)>'
   # ./spec/support/reset_rails_queue_adapter.rb:12:in `block (2 levels) in <top (required)>'
   # ./spec/support/reset_good_job.rb:19:in `block (2 levels) in <top (required)>'
   # ./spec/support/database_cleaner.rb:14:in `block (3 levels) in <top (required)>'
   # /usr/local/rvm/gems/default/gems/database_cleaner-core-2.0.1/lib/database_cleaner/strategy.rb:30:in `cleaning'
   # /usr/local/rvm/gems/default/gems/database_cleaner-core-2.0.1/lib/database_cleaner/cleaners.rb:34:in `block (2 levels) in cleaning'
   # /usr/local/rvm/gems/default/gems/database_cleaner-core-2.0.1/lib/database_cleaner/cleaners.rb:35:in `cleaning'
   # ./spec/support/database_cleaner.rb:13:in `block (2 levels) in <top (required)>'

This made me believe that I'm not allowed to pass a Hash to the job itself. Now the error is much clearer:

 ArgumentError:
       Concurrency key must be a String, was Hash

This is technically a breaking change. Some types like Number, Time and Symbol were being cast to a String by rails automatically, this now raises an error. The readme says that the concurrency key must be a String, but it would be best for this to go in the next major version if accepted.

[bensheldon]

@Earlopain Thinking about this, it's too much of a breaking change: objects that previously could be coerced to a string will start raising exceptions.

Simply doing the coercion would avoid the issue you had of the value failing to cast (though still leaves open it not being understood that a complex object is being stringified)

[bensheldon]

Suggested change

	raise ArgumentError, "Concurrency key must be a String, was #{key.class}" unless key.is_a?(String)
	key
	key.to_s

[Earlopain]

@Earlopain Thinking about this, it's too much of a breaking change: objects that previously could be coerced to a string will start raising exceptions.

Simply doing the coercion would avoid the issue you had of the value failing to cast (though still leaves open it not being understood that a complex object is being stringified)

I don't think doing to_s would be a good idea considering that you can pass model instances to jobs. It trades one issue for another:

class ExampleJob < ApplicationJob
  include GoodJob::ActiveJobExtensions::Concurrency
  good_job_control_concurrency_with(perform_limit: 1, key: -> { arguments.first })

  def perform(arg)
    sleep 60
  end
end

ExampleJob.perform_later(ExampleModel.first)
# key: "#<ExampleModel:0x00007f892b76bea0>"
ExampleJob.perform_later(ExampleModel.first)
# key: "#<ExampleModel:0x00007f892d66ee38>"

Both jobs would execute in parallel.

I agree on it being a breaking change. I have no issues with this being put on the backlog for v4, whenever that might be.

[bensheldon]

Hmmm. I don't want to require it to be is_a?(String) because there are plenty of other classes that I think should be acceptable: String, Symbol, Numeric, Date/Time....

...though maybe that isn't as infinite as I feared and it would be fine to typecheck those.

I also wonder if it would be possible to catch the bad cast exception and raise an easier to understand error.

[Earlopain]

I like the approach of just catching the error. I changed the commit to do just that.