Using the subscript method `#[]` on a string has several overloads and
rather complex implementation. One of the overloads is the capability to
accept a regular expression and then run a match, then return the
receiver (if it matched) or one of the groups from the MatchData.

The function of the `UUID#cast` method is to cast a UUID to a type and
format acceptable by postgres. Naturally UUIDs are supposed to be
string and of a certain format, but it had been determined that it was
not ideal for the framework to send just any old string to Postgres and
allow the engine to complain when "foobar" or "" was sent, being
obviously of the wrong format for a valid UUID. Therefore this code was
written to facilitate the checking, and if it were not of the correct
format, a `nil` would be returned as is conventional in Rails.

Now, the subscript method will allocate one or more strings on a match
and return one of them, based on the index parameter. However, there
is no need for a new string, as a UUID of the correct format is already
such, and so long as the format was verified then the string supplied is
adequate for consumption by the database.

The subscript method also creates a MatchData object which will never be
used, and so must eventually be garbage collected.

Garbage collection indeed. This innocuous method tends to be called
quite a lot, for example if the primary key of a table is a uuid, then
this method will be called. If the foreign key of a relation is a UUID,
once again this method is called. If that foreign key is belonging to
a has_many relationship with dozens of objects, then again dozens of
UUIDs shall be cast to a dup of themselves, and spawn dozens of
MatchData objects, and so on.

So, for users that:
* Use UUIDs as primary keys
* Use Postgres
* Operate on collections of objects

This accomplishes a significant savings in total allocations, and may
save many garbage collections.

Pass the template format to the digestor

Reset column info after making Topic tz-aware

Introduce delete_by and destroy_by methods to ActiveRecord::Relation

This reverts commit 6b69ae51, reversing
changes made to 84bd9ada.

Reason: We already use "happen" a lots for callbacks and validations.

https://github.com/rails/rails/pull/35324#issuecomment-465096483

[ci skip]

Update active_record_callbacks.md [ci skip]

Change 'happen' to a more technical term

Don't allow `where` with invalid value matches to nil values

In AttributeMethodsTest, we make the global Topic class time zone-aware
which changes instance date time attribute casting behaviour. We need to
reset column info after the test because future tests don't expect Topic
date time columns to be time zone-aware.

Actionpack typo fix

[ci skip]

When reloading is disabled, after_initialize hooks run after to_prepare hooks have already run for the last time. Since to_prepare hooks always run after application initializers, we don't need need to use an after_initialize hook.

That is considered as silently leaking information.
If type casting doesn't return any actual value, it should not be
matched to any record.

Fixes #33624.
Closes #33946.

Return correct date in ActiveModel for time to date conversions

Since `serialize` is passed user input args (from `where`, schema
default, etc), a helper should provide `serialize` if the helper also
provide `cast`.

Related #32624, 34cc301f, a741208f.

This is covered by `test_update_all_with_order_and_limit_updates_subset_only`
and `test_update_all_with_order_and_limit_and_offset_updates_subset_only`.

`value_from_multiparameter_assignment` defined by
`AcceptsMultiparameterTime` helper requires `default_timezone` method
which is defined at `TimeValue` helper.
Since `Date` type doesn't include `TimeValue`, I've extracted `Timezone`
helper to be shared by `Date`, `DateTime`, and `Time` types.

Before:

```
SELECT "comments".* FROM "comments" WHERE "comments"."type" IN ('VerySpecialComment') AND "comments"."post_id" = ? LIMIT ?  [["post_id", 4], ["LIMIT", 1]]
```

After:

```
SELECT "comments".* FROM "comments" WHERE "comments"."type" = ? AND "comments"."post_id" = ? LIMIT ?  [["type", "VerySpecialComment"], ["post_id", 4], ["LIMIT", 1]]
```

This fixes a bug that the `foreign_key` and the `foreign_type` are
separated as different table conditions if a polymorphic association has
a scope that joins another tables.

Auto correct rubocop offenses

Offenses:

railties/lib/rails/autoloaders.rb:1:1: C: [Corrected] Style/FrozenStringLiteralComment: Missing magic comment # frozen_string_literal: true.
module Rails
^
actionmailer/test/base_test.rb:917:1: C: [Corrected] Layout/EmptyLinesAroundBlockBody: Extra empty line detected at block body beginning.
actionmailer/test/base_test.rb:917:1: C: [Corrected] Layout/TrailingWhitespace: Trailing whitespace detected.
actionmailer/test/base_test.rb:917:5: C: [Corrected] Style/RedundantBegin: Redundant begin block detected.
    begin
    ^^^^^
actionmailer/test/base_test.rb:918:3: C: [Corrected] Layout/IndentationWidth: Use 2 (not 4) spaces for indentation.
      events = []
  ^^^^
actionmailer/test/base_test.rb:930:1: C: [Corrected] Layout/EmptyLinesAroundBlockBody: Extra empty line detected at block body end.
actionmailer/test/base_test.rb:930:1: C: [Corrected] Layout/TrailingWhitespace: Trailing whitespace detected.

Raise ActiveRecord::IrreversibleOrderError if nulls first/last is not a single ordering argument.

This follows up 0ee96d13.

Fix the regex that extract mismatched foreign key information

The CI failure for `test_errors_for_bigint_fks_on_integer_pk_table` is
due to the poor regex that extract all ``` `(\w+)` ``` like parts from
the message (`:foreign_key` should be `"old_car_id"`, but `"engines"`):

https://travis-ci.org/rails/rails/jobs/494123455#L1703

I've improved the regex more strictly and have more exercised mismatched
foreign key tests.

Fixes #35294

Fix possible memory leak of ConnectionHandler

refs #35296

Show deprecated message instead of raise exception in `compiled_method_container` method

Since #35212, foreign key feature is supported by all adapters.

[ci skip]

Properly handle cached queries with too many bind parameters