Association count with include doesn't alias join table

Let's say we have a has_many :through association:

class Author < ActiveRecord::Base
  has_many :authorships
  has_many :books, :through => :authorships
end

If we are performing a find on books we have the ability to include authorships:

author.books.find(:all, :include => :authorships, :conditions => ["authorships.primary = ?", true])

This works without error. However, if we try to do the same thing for a count:

author.books.count(:include => :authorships, :conditions => ["authorships.primary = ?", true])

We get an error (at least on mysql and sqlite) because it doesn't like it that we are including the authorships table even though it is already included in the join. This leads to an error like this:

ActiveRecord::StatementInvalid: Mysql::Error: Not unique table/alias: 'authorships'

The find call is smart enough to alias the join table with another name, but the count call isn't. The attachment includes a failing test to duplicate this.

Now you may be wondering why add the redundant :include option. In this simple example it's not really necessary, but in more complex examples it can be. Either way I think the count join should behave like the find join.

Seeing this change in behavior makes me think there's a way to DRY up how joins are handled between find and count.