*   Fix file descriptor being leaked on each call to `Kernel.silence_stream`.

    *Mario Visic*

*   Ensure `config.i18n.enforce_available_locales` is set before any other
    configuration option.

    *Yves Senn*

*   Added `Date#all_week/month/quarter/year` for generating date ranges.

    *Dmitriy Meremyanin*

*   Add `Time.zone.yesterday` and `Time.zone.tomorrow`. These follow the
    behavior of Ruby's `Date.yesterday` and `Date.tomorrow` but return localized
    versions, similar to how `Time.zone.today` has returned a localized version
    of `Date.today`.

    *Colin Bartlett*

*   Show valid keys when `assert_valid_keys` raises an exception, and show the
    wrong value as it was entered.

    *Gonzalo Rodríguez-Baltanás Díaz*

*   Both `cattr_*` and `mattr_*` method definitions now live in `active_support/core_ext/module/attribute_accessors`.

    Requires to `active_support/core_ext/class/attribute_accessors` are
    deprecated and will be removed in Ruby on Rails 4.2.

    *Genadi Samokovarov*

*   Deprecated `Numeric#{ago,until,since,from_now}`, the user is expected to explicitly
    convert the value into an AS::Duration, i.e. `5.ago` => `5.seconds.ago`

    This will help to catch subtle bugs like:

        def recent?(days = 3)
          self.created_at >= days.ago
        end

    The above code would check if the model is created within the last 3 **seconds**.

    In the future, `Numeric#{ago,until,since,from_now}` should be removed completely,
    or throw some sort of errors to indicate there are no implicit conversion from
    Numeric to AS::Duration.

    *Godfrey Chan*

*   Requires JSON gem version 1.7.7 or above due to a security issue in older versions.

    *Godfrey Chan*

*   Removed the old pure-Ruby JSON encoder and switched to a new encoder based on the built-in JSON
    gem.

    Support for encoding `BigDecimal` as a JSON number, as well as defining custom `encode_json`
    methods to control the JSON output has been **removed from core**. The new encoder will always
    encode BigDecimals as `String`s and ignore any custom `encode_json` methods.

    The old encoder has been extracted into the `activesupport-json_encoder` gem. Installing that
    gem will bring back the ability to encode `BigDecimal`s as numbers as well as `encode_json`
    support.

    Setting the related configuration `ActiveSupport.encode_big_decimal_as_string` without the
    `activesupport-json_encoder` gem installed will raise an error.

    *Godfrey Chan*

*   Add `ActiveSupport::Testing::TimeHelpers#travel` and `#travel_to`. These methods change current
    time to the given time or time difference by stubbing `Time.now` and `Date.today` to return the
    time or date after the difference calculation, or the time or date that got passed into the
    method respectively.

    Example for `#travel`:

        Time.now # => 2013-11-09 15:34:49 -05:00
        travel 1.day
        Time.now # => 2013-11-10 15:34:49 -05:00
        Date.today # => Sun, 10 Nov 2013

    Example for `#travel_to`:

        Time.now # => 2013-11-09 15:34:49 -05:00
        travel_to Time.new(2004, 11, 24, 01, 04, 44)
        Time.now # => 2004-11-24 01:04:44 -05:00
        Date.today # => Wed, 24 Nov 2004

    Both of these methods also accept a block, which will return the current time back to its
    original state at the end of the block:

        Time.now # => 2013-11-09 15:34:49 -05:00

        travel 1.day do
          User.create.created_at # => Sun, 10 Nov 2013 15:34:49 EST -05:00
        end

        travel_to Time.new(2004, 11, 24, 01, 04, 44) do
          User.create.created_at # => Wed, 24 Nov 2004 01:04:44 EST -05:00
        end

        Time.now # => 2013-11-09 15:34:49 -05:00

    This module is included in `ActiveSupport::TestCase` automatically.

    *Prem Sichanugrist*, *DHH*

*   Unify `cattr_*` interface: allow to pass a block to `cattr_reader`.

    Example:

        class A
          cattr_reader(:defr) { 'default_reader_value' }
        end
        A.defr # => 'default_reader_value'

    *Alexey Chernenkov*

*   Improved compatibility with the stdlib JSON gem.

    Previously, calling `::JSON.{generate,dump}` sometimes causes unexpected
    failures such as intridea/multi_json#86.

    `::JSON.{generate,dump}` now bypasses the ActiveSupport JSON encoder
    completely and yields the same result with or without ActiveSupport. This
    means that it will **not** call `as_json` and will ignore any options that
    the JSON gem does not natively understand. To invoke ActiveSupport's JSON
    encoder instead, use `obj.to_json(options)` or
    `ActiveSupport::JSON.encode(obj, options)`.

    *Godfrey Chan*

*   Fix Active Support `Time#to_json` and `DateTime#to_json` to return 3 decimal
    places worth of fractional seconds, similar to `TimeWithZone`.

    *Ryan Glover*

*   Removed circular reference protection in JSON encoder, deprecated
    `ActiveSupport::JSON::Encoding::CircularReferenceError`.

    *Godfrey Chan*, *Sergio Campamá*

*   Add `capitalize` option to `Inflector.humanize`, so strings can be humanized without being capitalized:

        'employee_salary'.humanize                    # => "Employee salary"
        'employee_salary'.humanize(capitalize: false) # => "employee salary"

    *claudiob*

*   Fixed `Object#as_json` and `Struct#as_json` not working properly with options. They now take
    the same options as `Hash#as_json`:

        struct = Struct.new(:foo, :bar).new
        struct.foo = "hello"
        struct.bar = "world"
        json = struct.as_json(only: [:foo]) # => {foo: "hello"}

    *Sergio Campamá*, *Godfrey Chan*

*   Added `Numeric#in_milliseconds`, like `1.hour.in_milliseconds`, so we can feed them to JavaScript functions like `getTime()`.

    *DHH*

*   Calling `ActiveSupport::JSON.decode` with unsupported options now raises an error.

    *Godfrey Chan*

*   Support `:unless_exist` in `FileStore`.

    *Michael Grosser*

*   Fix `slice!` deleting the default value of the hash.

    *Antonio Santos*

*   `require_dependency` accepts objects that respond to `to_path`, in
    particular `Pathname` instances.

    *Benjamin Fleischer*

*   Disable the ability to iterate over Range of AS::TimeWithZone
    due to significant performance issues.

    *Bogdan Gusiev*

*   Allow attaching event subscribers to ActiveSupport::Notifications namespaces
    before they're defined. Essentially, this means instead of this:

        class JokeSubscriber < ActiveSupport::Subscriber
          def sql(event)
            puts "A rabbi and a priest walk into a bar..."
          end

          # This call needs to happen *after* defining the methods.
          attach_to "active_record"
        end

    You can do this:

        class JokeSubscriber < ActiveSupport::Subscriber
          # This is much easier to read!
          attach_to "active_record"

          def sql(event)
            puts "A rabbi and a priest walk into a bar..."
          end
        end

    This should make it easier to read and understand these subscribers.

    *Daniel Schierbeck*

*   Add `Date#middle_of_day`, `DateTime#middle_of_day` and `Time#middle_of_day` methods.

    Also added `midday`, `noon`, `at_midday`, `at_noon` and `at_middle_of_day` as aliases.

    *Anatoli Makarevich*

*   Fix ActiveSupport::Cache::FileStore#cleanup to no longer rely on missing each_key method.

    *Murray Steele*

*   Ensure that autoloaded constants in all-caps nestings are marked as
    autoloaded.

    *Simon Coffey*

*   Add `String#remove(pattern)` as a short-hand for the common pattern of
    `String#gsub(pattern, '')`.

    *DHH*

*   Adds a new deprecation behaviour that raises an exception. Throwing this
    line into +config/environments/development.rb+

        ActiveSupport::Deprecation.behavior = :raise

    will cause the application to raise an +ActiveSupport::DeprecationException+
    on deprecations.

    Use this for aggressive deprecation cleanups.

    *Xavier Noria*

*   Remove 'cow' => 'kine' irregular inflection from default inflections.

    *Andrew White*

*   Add `DateTime#to_s(:iso8601)` and `Date#to_s(:iso8601)` for consistency.

    *Andrew White*

*   Add `Time#to_s(:iso8601)` for easy conversion of times to the iso8601 format for easy Javascript date parsing.

    *DHH*

*   Improve `ActiveSupport::Cache::MemoryStore` cache size calculation.
    The memory used by a key/entry pair is calculated via `#cached_size`:

        def cached_size(key, entry)
          key.to_s.bytesize + entry.size + PER_ENTRY_OVERHEAD
        end

    The value of `PER_ENTRY_OVERHEAD` is 240 bytes based on an [empirical
    estimation](https://gist.github.com/ssimeonov/6047200) for 64-bit MRI on
    1.9.3 and 2.0. GH#11512

    *Simeon Simeonov*

*   Only raise `Module::DelegationError` if it's the source of the exception.

    Fixes #10559

    *Andrew White*

*   Make `Time.at_with_coercion` retain the second fraction and return local time.

    Fixes #11350

    *Neer Friedman*, *Andrew White*

*   Make `HashWithIndifferentAccess#select` always return the hash, even when
    `Hash#select!` returns `nil`, to allow further chaining.

    *Marc Schütz*

*   Remove deprecated `String#encoding_aware?` core extensions (`core_ext/string/encoding`).

    *Arun Agrawal*

*   Remove deprecated `Module#local_constant_names` in favor of `Module#local_constants`.

    *Arun Agrawal*

*   Remove deprecated `DateTime.local_offset` in favor of `DateTime.civil_from_fromat`.

    *Arun Agrawal*

*   Remove deprecated `Logger` core extensions (`core_ext/logger.rb`).

    *Carlos Antonio da Silva*

*   Remove deprecated `Time#time_with_datetime_fallback`, `Time#utc_time`
    and `Time#local_time` in favor of `Time#utc` and `Time#local`.

    *Vipul A M*

*   Remove deprecated `Hash#diff` with no replacement.

    If you're using it to compare hashes for the purpose of testing, please use
    MiniTest's `assert_equal` instead.

    *Carlos Antonio da Silva*

*   Remove deprecated `Date#to_time_in_current_zone` in favor of `Date#in_time_zone`.

    *Vipul A M*

*   Remove deprecated `Proc#bind` with no replacement.

    *Carlos Antonio da Silva*

*   Remove deprecated `Array#uniq_by` and `Array#uniq_by!`, use native
    `Array#uniq` and `Array#uniq!` instead.

    *Carlos Antonio da Silva*

*   Remove deprecated `ActiveSupport::BasicObject`, use `ActiveSupport::ProxyObject` instead.

    *Carlos Antonio da Silva*

*   Remove deprecated `BufferedLogger`, use `ActiveSupport::Logger` instead.

    *Yves Senn*

*   Remove deprecated `assert_present` and `assert_blank` methods, use `assert
    object.blank?` and `assert object.present?` instead.

    *Yves Senn*

*   Fix return value from `BacktraceCleaner#noise` when the cleaner is configured
    with multiple silencers.

    Fixes #11030

    *Mark J. Titorenko*

*   `HashWithIndifferentAccess#select` now returns a `HashWithIndifferentAccess`
    instance instead of a `Hash` instance.

    Fixes #10723

    *Albert Llop*

*   Add `DateTime#usec` and `DateTime#nsec` so that `ActiveSupport::TimeWithZone` keeps
    sub-second resolution when wrapping a `DateTime` value.

    Fixes #10855

    *Andrew White*

*   Fix `ActiveSupport::Dependencies::Loadable#load_dependency` calling
    `#blame_file!` on Exceptions that do not have the Blamable mixin

    *Andrew Kreiling*

*   Override `Time.at` to support the passing of Time-like values when called with a single argument.

    *Andrew White*

*   Prevent side effects to hashes inside arrays when
    `Hash#with_indifferent_access` is called.

    Fixes #10526

    *Yves Senn*

*   Removed deprecated `ActiveSupport::JSON::Variable` with no replacement.

    *Toshinori Kajihara*

*   Raise an error when multiple `included` blocks are defined for a Concern.
    The old behavior would silently discard previously defined blocks, running
    only the last one.

    *Mike Dillon*

*   Replace `multi_json` with `json`.

    Since Rails requires Ruby 1.9 and since Ruby 1.9 includes `json` in the standard library,
    `multi_json` is no longer necessary.

    *Erik Michaels-Ober*

*   Added escaping of U+2028 and U+2029 inside the json encoder.
    These characters are legal in JSON but break the Javascript interpreter.
    After escaping them, the JSON is still legal and can be parsed by Javascript.

    *Mario Caropreso + Viktor Kelemen + zackham*

*   Fix skipping object callbacks using metadata fetched via callback chain
    inspection methods (`_*_callbacks`)

    *Sean Walbran*

*   Add a `fetch_multi` method to the cache stores. The method provides
    an easy to use API for fetching multiple values from the cache.

    Example:

        # Calculating scores is expensive, so we only do it for posts
        # that have been updated. Cache keys are automatically extracted
        # from objects that define a #cache_key method.
        scores = Rails.cache.fetch_multi(*posts) do |post|
          calculate_score(post)
        end

    *Daniel Schierbeck*

Please check [4-0-stable](https://github.com/rails/rails/blob/4-0-stable/activesupport/CHANGELOG.md) for previous changes.