*   Add subsec to `ActiveSupport::TimeWithZone#inspect`.

    Before:

        Time.at(1498099140).in_time_zone.inspect
        # => "Thu, 22 Jun 2017 02:39:00 UTC +00:00"
        Time.at(1498099140, 123456780, :nsec).in_time_zone.inspect
        # => "Thu, 22 Jun 2017 02:39:00 UTC +00:00"
        Time.at(1498099140 + Rational("1/3")).in_time_zone.inspect
        # => "Thu, 22 Jun 2017 02:39:00 UTC +00:00"

    After:

        Time.at(1498099140).in_time_zone.inspect
        # => "Thu, 22 Jun 2017 02:39:00.000000000 UTC +00:00"
        Time.at(1498099140, 123456780, :nsec).in_time_zone.inspect
        # => "Thu, 22 Jun 2017 02:39:00.123456780 UTC +00:00"
        Time.at(1498099140 + Rational("1/3")).in_time_zone.inspect
        # => "Thu, 22 Jun 2017 02:39:00.333333333 UTC +00:00"

    *akinomaeni*

*   Calling `ActiveSupport::TaggedLogging#tagged` without a block now returns a tagged logger.

    ```ruby
    logger.tagged("BCX").info("Funky time!") # => [BCX] Funky time!
    ```

    *Eugene Kenny*

*   Align `Range#cover?` extension behavior with Ruby behavior for backwards ranges.

    `(1..10).cover?(5..3)` now returns `false`, as it does in plain Ruby.

    Also update `#include?` and `#===` behavior to match.

    *Michael Groeneman*

*   Update to TZInfo v2.0.0.

    This changes the output of `ActiveSupport::TimeZone.utc_to_local`, but
    can be controlled with the
    `ActiveSupport.utc_to_local_returns_utc_offset_times` config.

    New Rails 6.1 apps have it enabled by default, existing apps can upgrade
    via the config in config/initializers/new_framework_defaults_6_1.rb

    See the `utc_to_local_returns_utc_offset_times` documentation for details.

    *Phil Ross*, *Jared Beck*

*   Add Date and Time `#yesterday?` and `#tomorrow?` alongside `#today?`.

    Aliased to `#prev_day?` and `#next_day?` to match the existing `#prev/next_day` methods.

    *Jatin Dhankhar*

*   Add `Enumerable#pick` to complement `ActiveRecord::Relation#pick`.

    *Eugene Kenny*

*   [Breaking change] `ActiveSupport::Callbacks#halted_callback_hook` now receive a 2nd argument:

    `ActiveSupport::Callbacks#halted_callback_hook` now receive the name of the callback
    being halted as second argument.
    This change will allow you to differentiate which callbacks halted the chain
    and act accordingly.

    ```ruby
      class Book < ApplicationRecord
        before_save { throw(:abort) }
        before_create { throw(:abort) }

        def halted_callback_hook(filter, callback_name)
          Rails.logger.info("Book couldn't be #{callback_name}d")
        end

        Book.create # => "Book couldn't be created"
        book.save # => "Book couldn't be saved"
      end
    ```

    *Edouard Chin*

*   Support `prepend` with `ActiveSupport::Concern`.

    Allows a module with `extend ActiveSupport::Concern` to be prepended.

        module Imposter
          extend ActiveSupport::Concern

          # Same as `included`, except only run when prepended.
          prepended do
          end
        end

        class Person
          prepend Imposter
        end

    Class methods are prepended to the base class, concerning is also
    updated: `concerning :Imposter, prepend: true do`.

    *Jason Karns*, *Elia Schito*

*   Deprecate using `Range#include?` method to check the inclusion of a value
    in a date time range. It is recommended to use `Range#cover?` method
    instead of `Range#include?` to check the inclusion of a value
    in a date time range.

    *Vishal Telangre*

*   Support added for a `round_mode` parameter, in all number helpers. (See: `BigDecimal::mode`.)

    ```ruby
    number_to_currency(1234567890.50, precision: 0, round_mode: :half_down) # => "$1,234,567,890"
    number_to_percentage(302.24398923423, precision: 5, round_mode: :down) # => "302.24398%"
    number_to_rounded(389.32314, precision: 0, round_mode: :ceil) # => "390"
    number_to_human_size(483989, precision: 2, round_mode: :up) # => "480 KB"
    number_to_human(489939, precision: 2, round_mode: :floor) # => "480 Thousand"

    485000.to_s(:human, precision: 2, round_mode: :half_even) # => "480 Thousand"
    ```

    *Tom Lord*

*   `Array#to_sentence` no longer returns a frozen string.

    Before:

        ['one', 'two'].to_sentence.frozen?
        # => true

    After:

        ['one', 'two'].to_sentence.frozen?
        # => false

    *Nicolas Dular*

*   When an instance of `ActiveSupport::Duration` is converted to an `iso8601` duration string, if `weeks` are mixed with `date` parts, the `week` part will be converted to days.
    This keeps the parser and serializer on the same page.

    ```ruby
    duration = ActiveSupport::Duration.build(1000000)
    # 1 week, 4 days, 13 hours, 46 minutes, and 40.0 seconds

    duration_iso = duration.iso8601
    # P11DT13H46M40S

    ActiveSupport::Duration.parse(duration_iso)
    # 11 days, 13 hours, 46 minutes, and 40 seconds

    duration = ActiveSupport::Duration.build(604800)
    # 1 week

    duration_iso = duration.iso8601
    # P1W

    ActiveSupport::Duration.parse(duration_iso)
    # 1 week
    ```

    *Abhishek Sarkar*

*   Add block support to `ActiveSupport::Testing::TimeHelpers#travel_back`.

    *Tim Masliuchenko*

*   Update `ActiveSupport::Messages::Metadata#fresh?` to work for cookies with expiry set when
    `ActiveSupport.parse_json_times = true`.

    *Christian Gregg*

*   Support symbolic links for `content_path` in `ActiveSupport::EncryptedFile`.

    *Takumi Shotoku*

*   Improve `Range#===`, `Range#include?`, and `Range#cover?` to work with beginless (startless)
    and endless range targets.

    *Allen Hsu*, *Andrew Hodgkinson*

*   Don't use `Process#clock_gettime(CLOCK_THREAD_CPUTIME_ID)` on Solaris.

    *Iain Beeston*

*   Prevent `ActiveSupport::Duration.build(value)` from creating instances of
    `ActiveSupport::Duration` unless `value` is of type `Numeric`.

    Addresses the errant set of behaviours described in #37012 where
    `ActiveSupport::Duration` comparisons would fail confusingly
    or return unexpected results when comparing durations built from instances of `String`.

    Before:

        small_duration_from_string = ActiveSupport::Duration.build('9')
        large_duration_from_string = ActiveSupport::Duration.build('100000000000000')
        small_duration_from_int = ActiveSupport::Duration.build(9)

        large_duration_from_string > small_duration_from_string
        # => false

        small_duration_from_string == small_duration_from_int
        # => false

        small_duration_from_int < large_duration_from_string
        # => ArgumentError (comparison of ActiveSupport::Duration::Scalar with ActiveSupport::Duration failed)

        large_duration_from_string > small_duration_from_int
        # => ArgumentError (comparison of String with ActiveSupport::Duration failed)

    After:

        small_duration_from_string = ActiveSupport::Duration.build('9')
        # => TypeError (can't build an ActiveSupport::Duration from a String)

    *Alexei Emam*

*   Add `ActiveSupport::Cache::Store#delete_multi` method to delete multiple keys from the cache store.

    *Peter Zhu*

*   Support multiple arguments in `HashWithIndifferentAccess` for `merge` and `update` methods, to
    follow Ruby 2.6 addition.

    *Wojciech Wnętrzak*

*   Allow initializing `thread_mattr_*` attributes via `:default` option.

        class Scraper
          thread_mattr_reader :client, default: Api::Client.new
        end

    *Guilherme Mansur*

*   Add `compact_blank` for those times when you want to remove #blank? values from
    an Enumerable (also `compact_blank!` on Hash, Array, ActionController::Parameters).

    *Dana Sherson*

*   Make ActiveSupport::Logger Fiber-safe.

    Use `Fiber.current.__id__` in `ActiveSupport::Logger#local_level=` in order
    to make log level local to Ruby Fibers in addition to Threads.

    Example:

        logger = ActiveSupport::Logger.new(STDOUT)
        logger.level = 1
        puts "Main is debug? #{logger.debug?}"

        Fiber.new {
          logger.local_level = 0
          puts "Thread is debug? #{logger.debug?}"
        }.resume

        puts "Main is debug? #{logger.debug?}"

    Before:

        Main is debug? false
        Thread is debug? true
        Main is debug? true

    After:

        Main is debug? false
        Thread is debug? true
        Main is debug? false

    Fixes #36752.

    *Alexander Varnin*

*   Allow the `on_rotation` proc used when decrypting/verifying a message to be
    passed at the constructor level.

    Before:

        crypt = ActiveSupport::MessageEncryptor.new('long_secret')
        crypt.decrypt_and_verify(encrypted_message, on_rotation: proc { ... })
        crypt.decrypt_and_verify(another_encrypted_message, on_rotation: proc { ... })

    After:

        crypt = ActiveSupport::MessageEncryptor.new('long_secret', on_rotation: proc { ... })
        crypt.decrypt_and_verify(encrypted_message)
        crypt.decrypt_and_verify(another_encrypted_message)

    *Edouard Chin*

*   `delegate_missing_to` would raise a `DelegationError` if the object
    delegated to was `nil`. Now the `allow_nil` option has been added to enable
    the user to specify they want `nil` returned in this case.

    *Matthew Tanous*

*   `truncate` would return the original string if it was too short to be truncated
    and a frozen string if it were long enough to be truncated. Now truncate will
    consistently return an unfrozen string regardless. This behavior is consistent
    with `gsub` and `strip`.

    Before:

        'foobar'.truncate(5).frozen?
        # => true
        'foobar'.truncate(6).frozen?
        # => false

    After:

        'foobar'.truncate(5).frozen?
        # => false
        'foobar'.truncate(6).frozen?
        # => false

    *Jordan Thomas*


Please check [6-0-stable](https://github.com/rails/rails/blob/6-0-stable/activesupport/CHANGELOG.md) for previous changes.