The ActiveSupport test suite only passes currently if it uses the latest unreleased commits for dalli, and a patch for Builder:
https://github.com/tenderlove/builder/pull/6

Beyond that, all external dependencies (at least, to the extent they’re used by ActiveSupport) are happy, including Nokogiri as of 1.8.0.

See https://github.com/rails/rails/issues/29067#issuecomment-301342084
for rationale.

This reverts commit b76f82d7.

Fixes #29067. Fixes #29081.

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`.

This retains the existing behavior of
ActiveSupport::Cache.expand_cache_key (as used by etaging) where the
cache key includes the version.

This reverts commit b86631d9, reversing
changes made to 8776a713.

ActiveSupport::Notifications is loaded using autoload that is defined by
the top level file of `active_support`. All the frameworks of Rails
requires the top level files before using any of the others files inside
the framework because the top level file is what setup the autoload
hooks and require the common dependencies.

Right now, if you install the current release version of Active Support (5.0.2) and try to use its cache implementation standalone by requiring `active_support/cache`, it crashes with `NameError: uninitialized constant ActiveSupport::Notifications`.  `AS::Notifications` is used in `cache.rb` down around [line 555](https://github.com/rails/rails/blob/8776a7139757d0b264785c774d4e7f37d4bc1ac7/activesupport/lib/active_support/cache.rb#L555).

Here's a quick repro script:

```ruby
require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  gem "activesupport", "5.0.2"
end

require "active_support/cache"

cache_store = ActiveSupport::Cache::MemoryStore.new

cache_store.write('test', 'okay')
puts cache_store.read('test')
```

However, any version _newer_ than 5.0.2 passes.

This is because [this commit](https://github.com/rails/rails/commit/75924c4517c8f87712d3f59c11f10152ed57b9d8) inadvertently included `AS::Notifications` into `AS::Cache` (thus fixing the issue) by mixing [`AS::Deprecation` into `AS::Duration`](https://github.com/rails/rails/blob/75924c4517c8f87712d3f59c11f10152ed57b9d8/activesupport/lib/active_support/duration.rb#L4), giving you a nice require chain of [`Cache` including `Time`][1] [including `Duration`][2] [including `Deprecation`][3] [including `Behaviors`][4] [including `Notifications`][5].  Phew.

Aside from being not very explicit, the fact that the fixing is specifically done by `AS::Deprecation` means that this fix is probably only temporary (until the deprecation is removed).

This PR just makes the inclusion explicit to future-proof against this breakage.

(Ideally, this would also be backported to `5-0-stable` to get picked up in any subsequent point release.)

See also: https://github.com/rails/rails/pull/14667

[1]: https://github.com/rails/rails/blob/75924c4517c8f87712d3f59c11f10152ed57b9d8/activesupport/lib/active_support/cache.rb#L6
[2]: https://github.com/rails/rails/blob/75924c4517c8f87712d3f59c11f10152ed57b9d8/activesupport/lib/active_support/time.rb#L2
[3]: https://github.com/rails/rails/blob/75924c4517c8f87712d3f59c11f10152ed57b9d8/activesupport/lib/active_support/duration.rb#L4
[4]: https://github.com/rails/rails/blob/75924c4517c8f87712d3f59c11f10152ed57b9d8/activesupport/lib/active_support/deprecation.rb#L16
[5]: https://github.com/rails/rails/blob/75924c4517c8f87712d3f59c11f10152ed57b9d8/activesupport/lib/active_support/deprecation/behaviors.rb#L1

These files are not using `strip_heredoc`.

Closes #27976

`Benchmark` was removed at 4215e9ab

`#fetch_multi` in case did not cache hit, to write a cache using the block value.
https://github.com/rails/rails/blob/master/activesupport/lib/active_support/cache.rb#L383..L384

Therefore, block is a need to pass always, I think should check first.

Single backticks don't work with rdoc.

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

Move new CHANGELOG entry top [ci skip]

Remove parameter "options = nil" for #clear

The related option of this method, `expires_in` is documented
as expecting an `ActiveSupport::Duration` value. To minimize any sort of
ambiguity between duration options, this change also documents
`race_condition_ttl` accepting `ActiveSupport::Duration`.

- Raised an argument error if no block is passed to #fetch with
'force: true' option is set.
- Added tests for the same.

Reevaluating the log output generated from this instrumentation,
we've found that it wasn't all that useful in practice.

```
Caches multi read:
- views/david/2/4184ab71db6849621a4d8820fcd2c0ad
- views/david/2/4184ab71db6849621a4d8820fcd2c0ad
- views/david/3/4184ab71db6849621a4d8820fcd2c0ad
- views/david/3/4184ab71db6849621a4d8820fcd2c0ad
```

If rendering many templates the output is inscrutable, and it's impossible
to see how many cache misses there were.

Revert ca6aba7f and implement a better way later.

- Expect returns "new value 1" but, retuns nil, because output at thread is not finished. Move val_1 output to finished thread.

Fixes https://github.com/rails/rails/issues/22477.

When I improved the caching instrumentation in
edd33c08, I inadvertently changed the
order of AS notifications when there is a cache miss.

Before this change, you couldn't tell if a read was a hit or not when
you called fetch.

When logging Cache key, in debug mode, also log namespace, to create the full key that actually used by the underline cache implementation

Skip the `:race_condition_ttl` branch if the option is 0 or nil. This fixes an issue with the redis cache, where this code will sometimes throw an error out of SETEX when passing 0 as the `expires_at`.

Adds `read_multi` instrumentation formatted as:

Caches multi read:
- views/david/2/4184ab71db6849621a4d8820fcd2c0ad
- views/david/2/4184ab71db6849621a4d8820fcd2c0ad
- views/david/3/4184ab71db6849621a4d8820fcd2c0ad
- views/david/3/4184ab71db6849621a4d8820fcd2c0ad