Also added the missing CHANGELOG entry for #12183 @ 80e75520 and
4d02296c.

Got all the tests passing again.

Support for `encode_json` has been removed (and consequently the
ability to encode `BigDecimal`s as numbers, as mentioned in the
previous commit). Install the `activesupport-json_encoder` gem
to get it back.

This is because the new encoder will no longer support encode_json.
Therefore our only choice is to return `to_i` or `to_s` in
`BigDecimal#as_json`. Since casting a BigDecimal to an integer is
most likely a lossy operation, we chose to encode it as a string.

Support for encoding BigDecimal as a string will return via the
`activesupport-json_encoder` gem.

In #12203, the JSON core extensions were moved into the `core_ext`
folder. Unfortunately, there are some corresponding requires that
were left behind. The problem is partially addressed in #12710, this
commit fixes the rest.

See [1] for why this is not a good idea.

As part of this refactor, circular reference protection in as_json has
been removed and the corresponding error class has been deprecated.

As discussed with @jeremy, circular reference error is considered
programmer errors and protecting against it is out of scope for
the encoder.

This is again based on the excellent work by @sergiocampama in #11728.

[1]: https://github.com/intridea/multi_json/pull/138#issuecomment-24468223

Same as #12710 but for the time module this time. This time it should
fix the Active Model test suite in isolation avoiding a TypeError to
be raised about the superclass of the DateTime object.

If we try to monkey-patch the class before requiring it, then a
"superclass mismatch" (TypeError) error is raised and the build can't
run correctly.

Fixes #12708

TL;DR The primary driver is to remove autoload surprise.

This is related to #12106. (The root cause for that ticket is that
json/add defines Regexp#to_json among others, but here I'll reproduce
the problem without json/add.)

Before:

   >> require 'active_support/core_ext/to_json'
   => true
   >> //.as_json
   NoMethodError: undefined method `as_json' for //:Regexp
     from (irb):3
     from /Users/godfrey/.rvm/rubies/ruby-2.0.0-p195/bin/irb:16:in `<main>'
   >> //.to_json
   => "\"(?-mix:)\""
   >> //.as_json
   => "(?-mix:)"

After:

   >> require 'active_support/core_ext/to_json'
   => true
   >> //.as_json
   => "(?-mix:)"

This is because ActiveSupport::JSON is autoloaded the first time
Object#to_json is called, which causes additional core extentions
(previously defined in active_support/json/encoding.rb) to be loaded.

When someone require 'active_support/core_ext', the expectation is
that it would add certain methods to the core classes NOW. The
previous behaviour causes additional methods to be loaded the first
time you call `to_json`, which could cause nasty surprises and other
unplesant side-effects.

This change moves all core extensions in to core_ext/json. AS::JSON is
still autoloaded on first #to_json call, but since it nolonger
include the core extensions, it should address the aforementioned bug.

*Requiring core_ext/object/to_json now causes a deprecation warnning*

Since Ruby 2.0 is UTF-8 by default we need to explictly say that the
encoding of this file is US-ASCII

U+2028 and U+2029 are allowed inside strings in JSON (as all literal
Unicode characters) but JavaScript defines them as newline
seperators. Because no literal newlines are allowed in a string, this
causes a ParseError in the browser. We work around this issue by
replacing them with the escaped version. The resulting JSON is still
valid and can be parsed in the browser.

This commit has been coauthored with Viktor Kelemen @yikulju

Currently, json/encoding respects the JSON spec (as it should) which 
disallows \n and \r inside strings, escaping them as expected.

Unfortunately, ECMA-262 (Javascript) disallows not only \n and \r in 
strings, but "Line Terminators" which includes U+2028 and U+2029. 
See here: http://bclary.com/2004/11/07/#a-7.3

This pull request adds U+2028 and U+2029 to be escaped.

# Why? 

It's very common to see something like this in a Rails template:

<script type="text/javascript"> 
var posts = <%= @posts.to_json %>;
</script>

If U+2028 or U+2029 are part of any attributes output in the to_json
call, you will end up with an exception.
In Chrome: Uncaught SyntaxError: Unexpected token ILLEGAL 

# Why not?

This is JSON encoding, and the JSON spec is specific about how to 
encode strings. U+2028 and U+2029 don't get special treatment.

Just trying to start a discussion... what do you do in your apps
to deal with this? Is there a convention I'm missing?

This reverts commit 046e27a7.
Check https://github.com/rails/rails/pull/8815#issuecomment-14026122 for
details.

The encoding scheme (e.g. ☠ -> "\u2620") was broken for characters
not in the Basic Multilingual Plane.  It is possible to escape them
for json using the weird encoding scheme of a twelve-character
sequence representing the UTF-16 surrogate pair (e.g. '𠜎' ->
"\u270e\u263a") but this wasn't properly handled in the escaping code.
Since raw UTF-8 is allowed in json, it was decided to simply pass
through the raw bytes rather than attempt to escape them.

Setting options in a custom `#as_json` method had side effects.
Modifications of the `options` hash leaked outside and influenced
the conversion of other objects contained in the hash.

This reverts commit 8896b4fd.

Conflicts:

	activemodel/lib/active_model.rb
	activemodel/lib/active_model/serializable.rb
	activemodel/lib/active_model/serializer.rb
	activemodel/test/cases/serializer_test.rb

The following constants were renamed:

  ActiveModel::Serialization     => ActiveModel::Serializable
  ActiveModel::Serializers::JSON => ActiveModel::Serializable::JSON
  ActiveModel::Serializers::Xml  => ActiveModel::Serializable::XML

The main motivation for such a change is that `ActiveModel::Serializers::JSON`
was not actually a serializer, but a module that when included allows the target to be serializable to JSON.

With such changes, we were able to clean up the namespace to add true serializers as the ArraySerializer.