Fixes #31762.

Ignores a default subclass when `becomes(Parent)`

Fixes issue described in #30399: A default value on the
inheritance column prevented `child.becomes(Parent)` to return
an instance of `Parent` as expected, instead it returns an instance
of the default subclass.

The change was introduced by #17169 and it was meant to affect
initialization, alone. Where `Parent.new` is expected to return
an instance of the default subclass.

Don't perform unnecessary check with false, just use true/false values

Don't update counter cache when through record was not destroyed

bin/yarn: Pass through arguments with spaces

Use singular define_attribute_method

`define_attribute_methods` splats the arguments,
then calls out to `define_attribute_method` for
each. When defining a singule attribute, using
the singular version of the method saves us an
array and an extra method call.

#30985 caused `object.save` performance regression since calling
`changes` in `changes_applied` is very slow.
We don't need to call the expensive method in `changes_applied` as long
as `@attributes` is tracked by mutation tracker.

https://gist.github.com/kamipo/1a9f4f3891803b914fc72ede98268aa2

Before:

```
Warming up --------------------------------------
create_string_columns
                        73.000  i/100ms
Calculating -------------------------------------
create_string_columns
                        722.256  (± 5.8%) i/s -      3.650k in   5.073031s
```

After:

```
Warming up --------------------------------------
create_string_columns
                        96.000  i/100ms
Calculating -------------------------------------
create_string_columns
                        950.224  (± 7.7%) i/s -      4.800k in   5.084837s
```

Previously, the `bin/yarn` wrapper would "unquote" arguments to yarn like this:
`yarn run add-copyright "(c) 2017, 2018 MyCompany"`
That results in an ARGV of ['run', 'add-copyright', '(c) 2017, 2018 MyCompany'] in the yarn wrapper,
but a ARGV in the yarn executable of ['run', 'add-copyright', '(c)',  '2017,', '2018', MyCompany']

Use dup'ed options hash

Fix typos and improve text_helper documentation regarding sanitization

[ci skip]

[ci skip]

Enable autocorrect for `Lint/EndAlignment` cop

This was added in #31727, but it is unused.

This test case which was added in #28287 checks that
`ActiveRecord::Schema.define` loads migration versions in
subdirectories. It should be kept it as it was.

Fix minor typo [ci skip]

Updated the method counts and unified them all on numerals.

Follow up to e1473e0c

* Depend on websocket-driver >= 0.6.1

Added a test around `NO_AUTO_VALUE_ON_ZERO`:

- Add set_locale to detect suitable locale
- Make feature compatible with Rails 5.x

* Support hash as first argument for `assert_difference`.

This allows to specify multiple numeric differences in the same assertion.
Example:

    assert_difference 'Article.count' => 1, 'Notification.count' => 2 do
      # post :create, params: { article: {...} }
    end

* Support error message when passing a hash as a first parameter

* Format CHANGELOG properly

[Julien Meichelbeck + Rafael Mendonça França]

Support for connection pooling on mem cache store

Added a note about bootsnap in the Rails 5.2 upgrade guide [ci skip]

Allow `false` for `config.generators.system_tests=`

down is only called with a block from the rake tasks where it passes a
`SCOPE`. Technically this was tested but since we don't run all the
migrations we're not actually testing the down works with a `SCOPE`. To
ensure we're testing both we can run `db:migrate` again to migrate users
and then run `down` with a scope to test that only the bukkits migration
is reverted.

Updates test to prevent having to fix regressions like we did in
4d4db4c8.

This slipped in as part of a2827ec9.

The UJS build has been failing with Chrome failed to start. This commit
fixes it by adding the option `--no-sandbox`. Travis removed the sanbox
option which is why Chrome crashes.

Ref https://github.com/travis-ci/travis-ci/issues/8836

Example failure: https://travis-ci.org/rails/rails/jobs/330396750

This reverts commit edc54fd2, reversing
changes made to a5922f13.

As discussed, this is not an appropriate place to make assumptions about
ARGV, or to write to stdout: config/boot.rb is a library and is required
by other applictions, with which we have no right to interfere.

Merge pull request #31727 from eileencodes/refactor-migration-classes-to-allow-for-migrations_paths-on-conn

Refactor migration to move migrations paths to connection

Rails has some support for multiple databases but it can be hard to
handle migrations with those. The easiest way to implement multiple
databases is to contain migrations into their own folder ("db/migrate"
for the primary db and "db/seconddb_migrate" for the second db). Without
this you would need to write code that allowed you to switch connections
in migrations. I can tell you from experience that is not a fun way to
implement multiple databases.

This refactoring is a pre-requisite for implementing other features
related to parallel testing and improved handling for multiple
databases.

The refactoring here moves the class methods from the `Migrator` class
into it's own new class `MigrationContext`. The goal was to move the
`migrations_paths` method off of the `Migrator` class and onto the
connection. This allows users to do the following in their
`database.yml`:

```
development:
  adapter: mysql2
  username: root
  password:

development_seconddb:
  adapter: mysql2
  username: root
  password:
  migrations_paths: "db/second_db_migrate"
```

Migrations for the `seconddb` can now be store in the
`db/second_db_migrate` directory. Migrations for the primary database
are stored in `db/migrate`".

The refactoring here drastically reduces the internal API for migrations
since we don't need to pass `migrations_paths` around to every single
method. Additionally this change does not require any Rails applications
to make changes unless they want to use the new public API. All of the
class methods from the `Migrator` class were `nodoc`'d except for the
`migrations_paths` and `migrations_path` getter/setters respectively.

### Summary

This PR changes .rubocop.yml.

Regarding the code using `if ... else ... end`, I think the coding style
that Rails expects is as follows.

```ruby
var = if cond
  a
else
  b
end
```

However, the current .rubocop.yml setting does not offense for the
following code.

```ruby
var = if cond
        a
      else
        b
      end
```

I think that the above code expects offense to be warned.
Moreover, the layout by autocorrect is unnatural.

```ruby
var = if cond
  a
      else
        b
      end
```

This PR adds a setting to .rubocop.yml to make an offense warning and
autocorrect as expected by the coding style.
And this change also fixes `case ... when ... end` together.

Also this PR itself is an example that arranges the layout using
`rubocop -a`.

### Other Information

Autocorrect of `Lint/EndAlignment` cop is `false` by default.
https://github.com/bbatsov/rubocop/blob/v0.51.0/config/default.yml#L1443

This PR changes this value to `true`.

Also this PR has changed it together as it is necessary to enable
`Layout/ElseAlignment` cop to make this behavior.