* add newline for display the fenced code block
* add "#" in the comments section

this allows us to construct mailer objects without possibly disastrous
side-effects.

Alias left_joins to left_outer_joins

Add test for parsing application/vnd.api+json

rails/application: allow passing an env to config_for

we should be using a countdown latch instead of rolling our own
busy-loop.

Make migrations concurrent safe (using advisory locks)

- Addresses issue #22092
- Works on Postgres and MySQL
- Uses advisory locks because of two important properties:
  1. The can be obtained outside of the context of a transaction
  2. They are automatically released when the session ends, so if a
  migration process crashed for whatever reason the lock is not left
  open perpetually
- Adds get_advisory_lock and release_advisory_lock methods to database
  adapters
- Attempting to run a migration while another one is in process will
  raise a ConcurrentMigrationError instead of attempting to run in
  parallel with undefined behavior. This could be rescued and
  the migration could exit cleanly instead. Perhaps as a configuration
  option?

Technical Notes
==============

The Migrator uses generate_migrator_advisory_lock_key to build the key
for the lock. In order to be compatible across multiple adapters there
are some constraints on this key.
- Postgres limits us to 64 bit signed integers
- MySQL advisory locks are server-wide so we have to scope to the
  database
- To fulfil these requirements we use a Migrator salt (a randomly
  chosen signed integer with max length of 31 bits) that identifies
  the Rails migration process as the owner of the lock. We multiply
  this salt with a CRC32 unsigned integer hash of the database name to
  get a signed 64 bit integer that can also be converted to a string
  to act as a lock key in MySQL databases.
- It is important for subsequent versions of the Migrator to use the
  same salt, otherwise different versions of the Migrator will not see
  each other's locks.

This assumes only one query was ever executed, but it appears to
sometimes be loading schema information. We can just look at the array
of queries, rather than the "first" one that was run

When testing cache issues, it is useful to log the actual key, including namespace

added ActiveRecord::Relation#outer_joins

We are using the same version constraint in the database adapters so
when a new version of the adapter that doesn't work with the version of
rails is released we don't break new applications.

This reverts commit 9f93a5ef.

Before this commit, if
`ActiveRecord::Base.belongs_to_required_by_default` is set to `true`,
then creating a record through `has_and_belongs_to_many` fails with the
cryptic error message `Left side must exist`. This is because
`inverse_of` isn't working properly in this case, presumably since we're
doing trickery with anonymous classes in the middle.

Rather than following this rabbit hole to try and get `inverse_of` to
work in a case that we know is not publicly supported, we can just turn
off this validation to match the behavior of 4.2 and earlier.

rather than an action name and *args.  The *args were not being used in regular
applications outside tests.  This causes a backwards compatibility
issue, but reduces array allocations for most users.

Support SQL sanitization in AR::QueryMethods#order

`dispatch` sets the request and response on the controller for us
automatically, so the test harness doesn't need to know the internals of
how request / response is set.

Conflicts:
	actionpack/lib/action_controller/test_case.rb

PostgreSQL, Replace static connection param list by libpq's dynamic list

Set standard_conforming_strings with SET

ActiveSupport::TimeWithZone documentation

This is part of a refactoring to make it easier to allow `order` to use
sanitize like just about everything else on relation. The deleted test
doesn't give any reasoning as to why passing `nil` to `order` needs to
be supported, and it's rather nonsensical. I can almost see allowing an
empty string being passed (though I'm tempted to just disallow it...)

default value for FixtureSet.fixture_class_names ought to be a Class

The stated value of `now` would actually give the same result for
`now - 24.hours` and `now - 1.day`. Use an alternative value for
`now` that demonstrates the difference between subtracting
`24.hours` and `1.day`.

Look at `TestFixtures.set_fixture_class`. As documented, it
accepts a mapping of fixture identifiers (string or symbol) to Classes
(the model classes that implement the named fixture).

Look now at the initialization of `TestFixtures.fixture_class_names`.
It defines a Hash, which will return a string by default (where the
string is the estimated class name of the given fixture identifier).

Now look at TestFixtures.load_fixtures. It calls `FixtureSet.create_fixtures`,
passing in the mapping of `fixture_class_names`.

Following this on to `FixtureSet.create_fixtures`, this instantiates a
`FixtureSet::ClassCache`, passing in the map of class names.

`ClassCache`, in turn, calls `insert_class` for each value in the cache.
(Recall that `set_fixture_class` puts Class objects in there, while the
default proc for the mapping puts String objects.)

Look finally at `insert_class`. If the value is present, it checks to
see if the value is a subclass of `AR::Base`. Fair enough...but wait!
What if the value is a String? You get an exception, because a String
instance cannot be compared with a Class.

Judging from the implementation, it seems like the expected behavior
here is for `fixture_class_names` to have no default proc. Look-ups are
supposed to happen via `ClassCache`, with `fixture_class_names` existing
solely as a repository for explicitly-registered class mappings.

That is what this change does.

Merge pull request #16252 from leckylao/actionview-date-helpers-selected-value-to-accept-hash-like-default

making date_helper selected value to accept Hash like the default option

making selected value to accept Hash like the default option. E.g. selected: {day: params[:day].to_i, month: params[:month].to_id}

Adds in test test_date_select_with_selected_in_hash and change log

fixes typo in CHANGELOG

This reverts commit 52439460.

This fixes an issue with the build where tests would fail on mysql and
postgresql due to different ordering.

Avoid disabling postgres errors

This reverts commit 6dc6a0b1, reversing
changes made to ec94f00b.

This pull request broke the build.