Now the following case will work fine

    class Tag < ActiveRecord::Base
    end

    class Publisher::Article < ActiveRecord::Base
      has_and_belongs_to_many :tags
    end

Fixes #15761

Fix habtm reflection
Conflicts:
    activerecord/CHANGELOG.md
    activerecord/lib/active_record/counter_cache.rb
    activerecord/lib/active_record/reflection.rb
    activerecord/test/cases/reflection_test.rb

Fixes #14824.

cc:
https://github.com/rails/rails/commit/a11e2fcff8cdc9691b977d8330abe63024f8c732#commitcomment-6353614
and 0369dbfd

parent_name is a string of nil, never a blank string so we don't need to
use presence.

Thank's for @laurocaetano for the help with tests. 😃

Fixes #14709

This is to get activerecord-deprecated_finders work again

All the job can be done at class level so we can avoid some object
allocation

Deprecated options `delete_sql`, `insert_sql`, `finder_sql` and `counter_sql`
have been deleted.

Method compilation provides better performance and I think the code
comes out cleaner as well.

A knock on effect is that methods that get redefined produce warnings. I
think this is a good thing. I had to deal with a bunch of warnings
coming from our tests, though.

Well, not all of them, but some of them.

I don't think there's much reason for these methods to be private.

This reverts commit 3803fcce.

Conflicts:
	activerecord/CHANGELOG.md

It will be deprecated only in 4.0, and removed properly in 4.1.

Improve the derivation of HABTM join table name to take account of nesting.
It now takes the table names of the two models, sorts them lexically and
then joins them, stripping any common prefix from the second table name.

Some examples:

  Top level models
  (Category <=> Product)
  Old: categories_products
  New: categories_products

  Top level models with a global table_name_prefix
  (Category <=> Product)
  Old: site_categories_products
  New: site_categories_products

  Nested models in a module without a table_name_prefix method
  (Admin::Category <=> Admin::Product)
  Old: categories_products
  New: categories_products

  Nested models in a module with a table_name_prefix method
  (Admin::Category <=> Admin::Product)
  Old: categories_products
  New: admin_categories_products

  Nested models in a parent model
  (Catalog::Category <=> Catalog::Product)
  Old: categories_products
  New: catalog_categories_products

  Nested models in different parent models
  (Catalog::Category <=> Content::Page)
  Old: categories_pages
  New: catalog_categories_content_pages

Also as part of this commit the validity checks for HABTM assocations have
been moved to ActiveRecord::Reflection One side effect of this is to move when
the exceptions are raised from the point of declaration to when the association
is built. This is consistant with other association validity checks.

Instead of generating association methods directly in the model
class, they are generated in an anonymous module which
is then included in the model class. There is one such module
for each association. The only subtlety is that the
generated_attributes_methods module (from ActiveModel) must
be forced to be included before association methods are created
so that attribute methods will not shadow association methods.

The old method of redefining destroy meant that clearing the HABTM join table would happen as long as the call to destroy succeeded.  Which meant if there was a before_destroy that stopped the instance being destroyed using normal means (returning false, raising ActiveRecord::Rollback) rather than exceptional means the join table would be cleared even though the instance wasn't destroyed.  Doing it in an after_destroy hook avoids this and has the advantage of happening inside the DB transaction too.

Use proper objects to do the work to build the associations (adding methods, callbacks etc) rather than calling a whole bunch of methods with rather long names.