Add deprecation for described_class change coming in 3.0.

[myronmarston]

This is the 2.99 counterpoint to #1361.

/cc @JonRowe

[JonRowe]

Seems legit to me, I liked the detection method ;)

[myronmarston]

Thanks for reviewing, @JonRowe.

[jjb]

This makes 2.99 incompatible with rails 4.0.5, right?

     Failure/Error: Unable to find matching line from backtrace
       --------------------------------------------------------------------------------
       The semantics of `described_class` in a nested `describe <SomeClass>`
       example group are changing in RSpec 3. In RSpec 2.x, `described_class`
       would return the outermost described class (SubscriptionsController).
       In RSpec 3, it will return the innermost described class (SubscriptionsController::ResponseHandler).
       In general, we recommend not describing multiple classes or objects in a
       nested manner as it creates confusion.

       To make your code compatible with RSpec 3, change from `described_class` to a reference
       to `SubscriptionsController::ResponseHandler`, or change the arg of the inner `describe` to a string.
       (Called from /Users/john/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/actionpack-4.0.5/lib/action_controller/test_case.rb:592:in `setup_controller_request_and_response')

[JonRowe]

It shouldn't do, unless you set a class name in an inner describe/context you should never see this message, and even if you're doing that simply changing it to use a string or specifying the subject directly would fix it. Can you gist your spec?

[jjb]

whoops, you are right -- after looking at my example the problem was obvious right away.

to be honest when i made the comment i was just blindingly going by the error message presented, which pointed to a line in rails 😳

(i blame the excellent detailed guidance in all the other deprecation warnings for making me lazy...)

[myronmarston]

i blame the excellent detailed guidance in all the other deprecation warnings for making me lazy...

Got it. We'll be sure to work hard at providing less detailed guidance when RSpec 4 rolls around in a few years.

[jjb]

:-D