PR #29163 introduced a change in behavior when a duration was
the denominator in a calculation - this was incorrect as dividing
by a duration should always return a `Numeric`. The behavior of
previous versions of Rails has been restored.

Fixes #29592.

The paragraphs retread ground covered by the title and the usage examples,
so let's just remove them.

[ Assain Jaleel & Kasper Timm Hansen ]

[ci skip]

[ Assain Jaleel & Kasper Timm Hansen ]

Rails.cache.write_multi foo: 'bar', baz: 'qux'

Plus faster `fetch_multi` with stores that implement `write_multi_entries`.
Keys that aren't found may be written to the cache store in one shot
instead of separate writes.

The default implementation simply calls `write_entry` for each entry.
Stores may override if they're capable of one-shot bulk writes, like
Redis `MSET`.

[ci skip]

[ci skip]

* Allow a default value to be declared for class_attribute

* Convert to using class_attribute default rather than explicit setter

* Removed instance_accessor option by mistake

* False is a valid default value

* Documentation

* Add ActiveSupport::CurrentAttributes to provide a thread-isolated attributes singleton

* Need to require first

* Move stubs into test namespace.

Thus they won't conflict with other Current and Person stubs.

* End of the line for you, whitespace!

* Support super in attribute methods.

Define instance level accessors in an included module such that
`super` in an overriden accessor works, akin to Active Model.

* Spare users the manual require.

Follow the example of concerns, autoload in the top level Active Support file.

* Add bidelegation support

* Rename #expose to #set. Simpler, clearer

* Automatically reset every instance.

Skips the need for users to actively embed something that resets
their CurrentAttributes instances.

* Fix test name; add tangible name value when blank.

* Try to ensure we run after a request as well.

* Delegate all missing methods to the instance

This allows regular `delegate` to serve, so we don't need bidelegate.

* Properly test resetting after execution cycle.

Also remove the stale puts debugging.

* Update documentation to match new autoreset

Previously calculations where the scalar is first would be converted
to a duration of seconds but this causes issues with dates being
converted to times, e.g:

    Time.zone = "Beijing"           # => Asia/Shanghai
    date = Date.civil(2017, 5, 20)  # => Mon, 20 May 2017
    2 * 1.day                       # => 172800 seconds
    date + 2 * 1.day                # => Mon, 22 May 2017 00:00:00 CST +08:00

Now the `ActiveSupport::Duration::Scalar` calculation methods will try
to maintain the part structure of the duration where possible, e.g:

    Time.zone = "Beijing"           # => Asia/Shanghai
    date = Date.civil(2017, 5, 20)  # => Mon, 20 May 2017
    2 * 1.day                       # => 2 days
    date + 2 * 1.day                # => Mon, 22 May 2017

Fixes #29160, #28970.

Previously apply_inflections would only use the :en uncountables
rather then the ones for the locale that was passed to pluralize or
singularize.

This changes apply_inflections to take a locale which it will use to
find the uncountables.

* Fix indentation.
* Add backticks.

* Remove trailing spaces.
* Add backticks around method and command.
* Fix indentation.

Send deprecation horizon and gem name as arguments to deprecation heavier handler, and make sure they are used for the ActiveSupport::Notifications message.

Support `:offset` in `Time#change` and `:zone` or `:offset`
in `ActiveSupport::TimeWithZone#change`.

Fixes #28723.

Was looking through #28402, and realized the CHANGELOG.md entry is in the wrong
place. Sorry we didn't catch this during code review 😢

[ci skip]

`fetch_values` was added to Hash in Ruby 2.3.0:
  https://bugs.ruby-lang.org/issues/10017

This patch adds an implemention for instances of HWAI, in line
with the existing definitions of `fetch` and `values_at`.

[ci skip]

An alternative to DeprecatedConstantProxy which works more transparently
with exceptions because it returns the object that the new constant
refers to rather than a proxy. This is then compatible with
`rescue OldException`.

In #28204 we deprecated implicit conversion of durations to a
numeric which represented the number of seconds in the duration
because of unwanted side effects with calculations on durations
and dates. This unfortunately had the side effect of forcing a
explicit cast when configuring third-party libraries like
expiration in Redis, e.g:

    redis.expire("foo", 5.minutes)

To work around this we've removed the deprecation and added a
private class that wraps the numeric and can perform calculation
involving durations and ensure that they remain a duration
irrespective of the order of operations.

[ci skip]

Handle #to_time and memoization taking into account memoization, frozen state, and preserve_timezone flag.

In 4b685aad the regex in `titlelize` was updated to not match
apostrophes to better reflect the nature of the transformation.
Unfortunately this had the side effect of breaking capitalization
on the first word of a sub-string, e.g:

  >> "This was 'fake news'".titleize
  => "This Was 'fake News'"

This is fixed by extending the look-behind to also check for a
word character on the other side of the apostrophe.

Fixes #28312.

For naming consistency when using the RFC 3339 profile
of ISO 8601 in applications.

The `Time.xmlschema` and consequently its alias `iso8601` accepts
timestamps without a offset in contravention of the RFC 3339
standard. This method enforces that constraint and raises an
`ArgumentError` if it doesn't.

Previously there was no way to get a RFC 3339 timestamp
into a specific timezone without either using `parse` or
chaining methods. The new method allows parsing directly
into the timezone, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.rfc3339("1999-12-31T14:00:00Z")
    => Fri, 31 Dec 1999 14:00:00 HST -10:00

This new method has stricter semantics than the current
`parse` method and will raise an `ArgumentError`
instead of returning nil, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.rfc3339("foobar")
    ArgumentError: invalid date
    >> Time.zone.parse("foobar")
    => nil

It will also raise an `ArgumentError` when either the
time or offset components are missing, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.rfc3339("1999-12-31")
    ArgumentError: invalid date
    >> Time.zone.rfc3339("1999-12-31T14:00:00")
    ArgumentError: invalid date

Previously there was no way to get a ISO 8601 timestamp into a specific
timezone without either using `parse` or chaining methods. The new method
allows parsing directly into the timezone, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.iso8601("1999-12-31T14:00:00Z")
    => Fri, 31 Dec 1999 14:00:00 HST -10:00

If the timestamp is a ISO 8601 date (YYYY-MM-DD) then the time is set
to midnight, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.iso8601("1999-12-31")
    => Fri, 31 Dec 1999 00:00:00 HST -10:00

This new method has stricter semantics than the current `parse` method
and will raise an `ArgumentError` instead of returning nil, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.iso8601("foobar")
    ArgumentError: invalid date
    >> Time.zone.parse("foobar")
    => nil

Currently `ActiveSupport::Duration` implicitly converts to a seconds
value when used in a calculation except for the explicit examples of
addition and subtraction where the duration is the receiver, e.g:

    >> 2 * 1.day
    => 172800

This results in lots of confusion especially when using durations
with dates because adding/subtracting a value from a date treats
integers as a day and not a second, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 2 * 1.day
    => Mon, 10 Apr 2490

To fix this we're implementing `coerce` so that we can provide a
deprecation warning with the intent of removing the implicit coercion
in Rails 5.2, e.g:

    >> 2 * 1.day
    DEPRECATION WARNING: Implicit coercion of ActiveSupport::Duration
    to a Numeric is deprecated and will raise a TypeError in Rails 5.2.
    => 172800

In Rails 5.2 it will raise `TypeError`, e.g:

    >> 2 * 1.day
    TypeError: ActiveSupport::Duration can't be coerced into Integer

This is the same behavior as with other types in Ruby, e.g:

    >> 2 * "foo"
    TypeError: String can't be coerced into Integer
    >> "foo" * 2
    => "foofoo"

As part of this deprecation add `*` and `/` methods to `AS::Duration`
so that calculations that keep the duration as the receiver work
correctly whether the final receiver is a `Date` or `Time`, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 1.day * 2
    => Fri, 03 Mar 2017

Fixes #27457.