In production the query cache was already being loaded before the first
request even without #33856, so added a test to make sure of it.

This new test is passing even if #33856 is reverted.

Include test helpers in ActionDispatch::IntegrationTest

As @dhh brings up, the point of `ActionDispatch::IntegrationTest` is to
allow users to test the integration of all the pieces called by a
controller. Asserting about the emails and jobs queued is part of that
task.

This commit includes the `ActionMailer::TestHelper` and
`ActiveJob::TestHelper` modules when the ActionMailer and ActiveJob
railties are initialized respectively.

Faster multiple_of? method

Follow up #33756

Also remove `# :nodoc:` for `ActiveRecord::Core::ClassMethods` in order
to show non-nodoc methods in that module on the api docs http://edgeapi.rubyonrails.org

It would allow `filter_attributes` to be reused across multiple
calls to `#inspect` or `#pretty_print`.

- Add `require "set"`
- Remove `filter_attributes` instance reader. I think there is no need
to keep it.

- Move
  ```
  filter_attributes = self.filter_attributes.map(&:to_s).to_set

  filter_attributes.include?(attribute_name) && !read_attribute(attribute_name).nil?
  ```
  to private method.

- Fix tests in `activerecord/test/cases/filter_attributes_test.rb`
  - Ensure that `teardown` sets `ActiveRecord::Base.filter_attributes` to
    previous state.

  - Ensure that `Admin::Account.filter_attributes` is set to previous
    state in the "filter_attributes could be overwritten by models" test.

Follow up #33756

Add mention that `config.filter_parameters` also filters out sensitive
values of database columns when call `#inspect` since #33756.

Fix query cache to load before first request

In a test app we observed that the query cache was not enabled on the
first request. This was because the query cache hooks are installed on
load and active record is loaded in the middle of the first request.

If we remove the `on_load` from the railtie the query cache hooks will
be installed before the first request, allowing the cache to be enabled
on that first request.

This is ok because query cache doesn't load anything else, only itself
so we're not eager loading all of active record before the first
request, just the query cache hooks.

[Eileen M. Uchitelle & Matthew Draper]

Update test_helper_test.rb

Fix typo `wiht` -> `with`

Update action_mailer_basics.md

Add backticks to code

Run yarn install relative to Rails.root

Disable content security policy for mailer previews

TaggedLogging to return a new logger instance

Move digest path calculation out of loop

Use ActiveSupport::InheritableOptions and deep_symbolize_keys in config_for

The name of the minitest library is spelled that way: regular font, and
lowercase. Lowercase is used even at the beginning of sentences, see

    http://docs.seattlerb.org/minitest/

I double-checked this with @zenspider too (thanks!).

Fix zero-byte files upload in #33630

On every iteration of generating a cache for a collection a “digest path” is calculated even though it’s exactly the same for every element.

This PR exposes a method `digest_path_from_virtual` that returns back a “digest_path”. This can in turn be passed back into `cache_fragment_name`. This not only does less work, but it also (you guessed it) uses  less memory.

before: Total allocated: 762539 bytes (7035 objects)
after: Total allocated: 743590 bytes (6621 objects) 


(762539 - 743590)/ 762539.0 # => 2.4% faster ⚡️⚡️

Clarify changelog entry added in #33779 [ci skip]

Skip delivery notification when perform_deliveries is false.

* Use utf8mb4 character set by default

`utf8mb4` character set supports supplementary characters including emoji.
`utf8` character set with 3-Byte encoding is not enough to support them.

There was a downside of 4-Byte length character set with MySQL 5.5 and 5.6:

"ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes"
for Rails string data type which is mapped to varchar(255) type.

MySQL 5.7 supports 3072 byte key prefix length by default.

* Remove `DEFAULT COLLATE` from Active Record unit test databases

There should be no "one size fits all" collation in MySQL 5.7.
Let MySQL server choose the default collation for Active Record
unit test databases.

Users can choose their best collation for their databases
by setting `options[:collation]` based on their requirements.

* InnoDB FULLTEXT indexes support since MySQL 5.6
it does not have to use MyISAM storage engine whose maximum key length is 1000 bytes.
Using MyISAM storag engine with utf8mb4 character set would cause
"Specified key was too long; max key length is 1000 bytes"

https://dev.mysql.com/doc/refman/5.6/en/innodb-fulltext-index.html

* References

"10.9.1 The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)"
https://dev.mysql.com/doc/refman/5.7/en/charset-unicode-utf8mb4.html

"10.9.2 The utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)"
https://dev.mysql.com/doc/refman/5.7/en/charset-unicode-utf8.html

"14.8.1.7 Limits on InnoDB Tables"
https://dev.mysql.com/doc/refman/5.7/en/innodb-restrictions.html
> If innodb_large_prefix is enabled (the default), the index key prefix limit is 3072 bytes
> for InnoDB tables that use DYNAMIC or COMPRESSED row format.

* CI against MySQL 5.7

Followed this instruction and changed root password to empty string.
https://docs.travis-ci.com/user/database-setup/#MySQL-57

* The recommended minimum version of MySQL is 5.7.9
to support utf8mb4 character set and `innodb_default_row_format`

MySQL 5.7.9 introduces `innodb_default_row_format` to support 3072 byte length index by default.
Users do not have to change MySQL database configuration to support Rails string type.

https://dev.mysql.com/doc/refman/5.7/en/innodb-parameters.html#sysvar_innodb_default_row_format

https://dev.mysql.com/doc/refman/5.7/en/innodb-restrictions.html
> If innodb_large_prefix is enabled (the default),
> the index key prefix limit is 3072 bytes for InnoDB tables that use DYNAMIC or COMPRESSED row format.

* The recommended minimum version of MariaDB is 10.2.2
MariaDB 10.2.2 is the first version of MariaDB supporting `innodb_default_row_format`
Also MariaDB says "MySQL 5.7 is compatible with MariaDB 10.2".

- innodb_default_row_format
https://mariadb.com/kb/en/library/xtradbinnodb-server-system-variables/#innodb_default_row_format

- "MariaDB versus MySQL - Compatibility"
https://mariadb.com/kb/en/library/mariadb-vs-mysql-compatibility/
> MySQL 5.7 is compatible with MariaDB 10.2

- "Supported Character Sets and Collations"
https://mariadb.com/kb/en/library/supported-character-sets-and-collations/

Pushing scope attributes was added at d4007d5a for fixing inheritance
object creation. But it was not a better fix, since we could just pull
that on demand in `Inheritance` module.

I'd like to use this `scoping` handling on klass level to address
unwanted internal scoping issues.

`scoping` stashes the reciever and then returning that as `klass.all`.
`all.scoping` has no effect to the public behavior, so it is redundant.

The `existing` arg was added at 8bc0fce0, but it is no longer used since
aac9da25.

Make sure there are no duplicated nested records with create_with

In order to avoid double assignments of nested_attributes for `has_many`
relations during record initialization, nested_attributes in `create_with`
should not be passed into `klass.new` and have them populate during
`initialize_internals_callback` with scope attributes.

However, `create_with` keys should always have precedence over where
clauses, so if there are same keys in both `create_with` and
`where_values_hash`, the value in `create_with` should be the one that's
used.

Follow up of 3e814907.

Followup to a recently merged PR, too minor and detailed to require a
modification to the contributed patch.

ActiveJob Backburner adapter: fix priority

Add #unfreeze_time to ActiveSupport::Testing::TimeHelpers