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*

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

As reported (https://github.com/rails/rails/pull/8185#issuecomment-11702226)
this test relied on the order a hash was serialized. Comparing the parsed
hash makes the test no longer order dependent.

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.

Reason: ActiveSupport::JSON::Variable is not used anymore internally. It
was deprecated in 3-2-stable but we reverted all the deprecation for
point releases.

See #6536 and #6546.
Conflicts:
	activesupport/lib/active_support/json/variable.rb

There are a bunch of other implicit branches that adds
1.8.x specific code that still needs to be removed. Pull
requests for those cases are welcome.

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

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

- as_json in ActiveModel should return a hash
  and handle :only/:except/:methods options
- Array and Hash should call as_json on their elements
- json methods should not modify options argument

[#5374 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

[#4979 state:committed]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

BigDecimal#as_json does not really specify the F format, it delegates that to whatever BigDecimal#to_s default format is, do the same in its test

Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

JSON: encode objects that don't have a native JSON representation using to_hash, if available, instead of instance_values (the old fallback) or to_s (other encoders' default). Encode BigDecimal and Regexp encode as strings to conform with other encoders. Try to transcode non-UTF-8 strings.

According to RFC 4627, only the following Unicode code points are
allowed unescaped in JSON:

  unescaped = %x20-21 / %x23-5B / %x5D-10FFFF

However, ActiveSupport::JSON did not escape the range %x00-1f.  This caused
parse errors when trying to decode the resulting output.

[#3345 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

[#2849 state:resolved]

    Example: ActiveSupport::JSON.backend = "JSONGem"

  All internal Rails JSON encoding is now handled by ActiveSupport::JSON.encode().  Use of #to_json is not recommended, as it may clash with other libraries that overwrite it.  However, you can recover Rails specific functionality
  if you really want to use #to_json.

    gem 'json'
    ActiveSupport::JSON.backend = "JSONGem"

    class ActiveRecord::Base
      alias to_json rails_to_json
    end

[#1617 state:resolved]

According to the RFC and the json.org site all json keys must be strings, and those strings must be quoted with double quotes.
[#1755 state:committed]

[#652 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>