Thanks to @jeremy to teach me this one.

This reverts commit 4e9f53f9, reversing
changes made to 6b802cdb.

Revert "Don't use tap in this case."

This reverts commit 454d820b.

Reason: Is not a good idea to add options to this method since we can do
the same thing using method composition.

    Person.validators_on(:name).select { |v| v.kind == :presence }

Also it avoids to change the method again to add more options.

The use of tap in this case is very confusing since we are mutating the
return value inside the block

This will filter out the validators on a particular attribute based on
its kind.

There's no need to create two extra hashes with options.merge(another_hash),
with the goal of setting only one value, so lets just set it.

Also refactor validates_each to use _merge_attributes, like other
validates_* helpers do.

Get rid of ActiveModel::Configuration, make better use of
ActiveSupport::Concern + class_attribute, etc.

This reverts commit fa6d921e.

Reason: Not a fan of such massive changes. We usually close such changes
if made to Rails master as a pull request. Following the same principle
here and reverting.

[ci skip]

For future reference, this is the regex I used: ^\s*#\s*\n(?!\s*#). Replace
with the first match, and voilà! Note that the regex matches a little bit too
much, so you probably want to `git add -i .` and go through every single diff
to check if it actually should be changed.

The problem: We need to be able to specify configuration in a way that
can be inherited to models that include ActiveRecord::Model. So it is
no longer sufficient to put 'top level' config on ActiveRecord::Base,
but we do want configuration specified on ActiveRecord::Base and
descendants to continue to work.

So we need something like class_attribute that can be defined on a
module but that is inherited when ActiveRecord::Model is included.

The solution: added ActiveModel::Configuration module which provides a
config_attribute macro. It's a bit specific hence I am not putting this
in Active Support or making it a 'public API' at present.

Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

[#5311 state: resolved]

ActiveModel::Validations uses Hash#except, but does not require it from
ActiveSupport.  (This wasn't showing up in the tests, because it was
required in the helper, and was also required in
ActiveModel::Serialization).
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

[#5311 state: resolved]

ActiveModel::Validations uses Hash#except, but does not require it from
ActiveSupport.  (This wasn't showing up in the tests, because it was
required in the helper, and was also required in
ActiveModel::Serialization).
Signed-off-by: NJosé Valim <jose.valim@gmail.com>