Fix `bin/rails db:setup` and `bin/rails db:test:prepare` create  wrong ar_internal_metadata's data for a test database.

  Before:
  ```
  $ RAILS_ENV=test rails dbconsole
  > SELECT * FROM ar_internal_metadata;
  key|value|created_at|updated_at
  environment|development|2017-09-11 23:14:10.815679|2017-09-11 23:14:10.815679
  ```

  After:
  ```
  $ RAILS_ENV=test rails dbconsole
  > SELECT * FROM ar_internal_metadata;
  key|value|created_at|updated_at
  environment|test|2017-09-11 23:14:10.815679|2017-09-11 23:14:10.815679
  ```

  Fixes #26731.

This test covers the case of 02da8aea.

Previously `exists?` was always eager-loading the includes values. But
now it is eager-loaded only when necessary since 07a611e0.

So the case of the eager-loading had not covered in the test.

We already found the longer sequence name, but we could not consider
whether it was the sequence name created by serial type due to missed a
max identifier length limitation. I've addressed the sequence name
consideration to respect the max identifier length.

Fixes #28332.

Currently `AUTO_INCREMENT` is implicitly used in the default primary key
definition. But `AUTO_INCREMENT` is not only used for single column
primary key, but also for composite primary key. In that case,
`auto_increment: true` should be dumped explicitly in the
`db/schema.rb`.

Fixes #30894.

This is the fix for the regression of #29848.

In #29848, I've kept existing select list in the subquery for the count
if ORDER BY is given. But it had accidentally affect to GROUP BY
queries also. It should keep the previous behavior in that case.

Fixes #30886.

For investigating the cause of failure.

https://travis-ci.org/rails/rails/jobs/287474883#L797-L799

Building association scope in join dependency should respect the parent
relation's aliases to avoid using the same alias name more than once.

Fixes #30681.

I don't think this is a good abstraction because the internal method is
used only if the relation need to be applied join dependency.

`relation.exists?` should reference correct aliases while joining tables
of has_many through associations.

s/Action Record/Active Record/

* When the adapter is missing, raise an exception that points out config
  typos and missing Gemfile entries. (We can assume that a non-builtin
  adapter was used since these are always available.)
* When loading an adapter raises a LoadError, prefix its error message
  to indicate that the adapter is likely missing an optional dependency.

This is preparation to respect parent relation's alias tracking for
fixing #30681.

Before

```
> Article.left_joins
ArgumentError: The method .left_outer_joins() must contain arguments.
```

After

```
> Article.left_joins
ArgumentError: The method .left_joins() must contain arguments.
```

Implemented by #22911
Related to #30677

* Add missing credit
* Add backticks
* Fix indentation
* Remove trailing spaces

And some minor tweaks.

Since #29301, `arel_attribute` respects a custom table name.

PostgreSQL 9.1+ introduced range types, and Rails added support for
using this datatype in ActiveRecord. However, the serialization of
`PostgreSQL::OID::Range` was incomplete, because it did not properly
quote the bounds that make up the range. A clear example of this is a
`tsrange`.

Normally, ActiveRecord quotes Date/Time objects to include the
milliseconds. However, the way `PostgreSQL::OID::Range` serialized its
bounds, the milliseconds were dropped. This meant that the value was
incomplete and not equal to the submitted value.

An example of normal timestamps vs. a `tsrange`. Note how the bounds
for the range do not include their milliseconds (they were present in
the ruby Range):

    UPDATE "iterations" SET "updated_at" = $1, "range" = $2 WHERE
    "iterations"."id" = $3
    [["updated_at", "2017-09-23 17:07:01.304864"],
    ["range", "[2017-09-23 00:00:00 UTC,2017-09-23 23:59:59 UTC]"],
    ["id", 1234]]

`PostgreSQL::OID::Range` serialized the range by interpolating a
string for the range, which works for most cases, but does not work
for timestamps:

    def serialize(value)
      if value.is_a?(::Range)
        from = type_cast_single_for_database(value.begin)
        to = type_cast_single_for_database(value.end)
        "[#{from},#{to}#{value.exclude_end? ? ')' : ']'}"
      else
        super
      end
    end

    (byebug) from = type_cast_single_for_database(value.begin)
    2010-01-01 13:30:00 UTC

    (byebug) to = type_cast_single_for_database(value.end)
    2011-02-02 19:30:00 UTC

    (byebug) "[#{from},#{to}#{value.exclude_end? ? ')' : ']'}"
    "[2010-01-01 13:30:00 UTC,2011-02-02 19:30:00 UTC)"

@sgrif (the original implementer for Postgres Range support) provided
some feedback about where the quoting should occur:

  Yeah, quoting at all is definitely wrong here. I'm not sure what I
  was thinking in 02579b56, but what this is doing is definitely in the
  wrong place. It should probably just be returning a range of
  subtype.serialize(value.begin) and subtype.serialize(value.end), and
  letting the adapter handle the rest.

`Postgres::OID::Range` now returns a `Range` object, and
`ActiveRecord::ConnectionAdapters::PostgreSQL::Quoting` can now encode
and quote a `Range`:

    def encode_range(range)
      "[#{type_cast(range.first)},#{type_cast(range.last)}#{range.exclude_end? ? ')' : ']'}"
    end

    ...

    encode_range(range)
    #=> "['2010-01-01 13:30:00.670277','2011-02-02 19:30:00.745125')"

This commit includes tests to make sure the milliseconds are
preserved in `tsrange` and `tstzrange` columns

These are no longer used since 66736c8e.

Because the reflection doesn't have `foreign_type` unless the
association is a polymorphic association.

I do not want to set the expectation that any enumerable object should
behave this way, but this case in particular comes up frequently enough
that I'm caving on this one.

Fixes #30684.

Benchmark Script:
```
require 'active_record'
require 'benchmark/ips'

ActiveRecord::Base.establish_connection(ENV.fetch('DATABASE_URL'))
ActiveRecord::Migration.verbose = false

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.string :name, :email
    t.integer :topic_id
    t.timestamps null: false
  end

  create_table :topics, force: true do |t|
    t.string :title
    t.timestamps null: false
  end
end

attributes = {
  name: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.',
  email: 'foobar@email.com'
}

class Topic < ActiveRecord::Base
  has_many :users
end

class User < ActiveRecord::Base
  belongs_to :topic
end

100.times do
  User.create!(attributes)
end

users = User.first(50)

Topic.create!(title: 'This is a topic', users: users)

Benchmark.ips do |x|
  x.config(time: 10, warmup: 5)

  x.report("preload") do
    User.includes(:topic).all.to_a
  end
end
```

Before:
```
Calculating -------------------------------------
             preload    40.000  i/100ms
-------------------------------------------------
             preload    407.962  (± 1.5%) i/s -      4.080k
```

After:
```
alculating -------------------------------------
             preload    43.000  i/100ms
-------------------------------------------------
             preload    427.567  (± 1.6%) i/s -      4.300k
```

I got this error in production using Puma in multi-threaded mode:

```
RuntimeError: Digest::Base cannot be directly inherited in Ruby
from active_support/security_utils.rb:23:in `variable_size_secure_compare'
from active_support/security_utils.rb:23:in `hexdigest'
from active_support/security_utils.rb:23:in `digest'
```

Looks like Digest uses const_missing to load Digest::SHA256 (https://github.com/ruby/ruby/blob/trunk/ext/digest/lib/digest.rb#L8)

- https://bugs.ruby-lang.org/issues/9494
- https://github.com/ruby/ruby/commit/c02fa39463a0c6bf698b01bc610135604aca2ff4

Benchmark Script

```
require 'active_record'
require 'benchmark/ips'
require 'ruby-prof'
require 'memory_profiler'
require 'byebug'

ActiveRecord::Base.establish_connection(ENV.fetch('DATABASE_URL'))
ActiveRecord::Migration.verbose = false

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.string :name, :email
    t.integer :topic_id
    t.timestamps null: false
  end

  create_table :topics, force: true do |t|
    t.string :title
    t.timestamps null: false
  end
end

attributes = {
  name: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.',
  email: 'foobar@email.com'
}

class Topic < ActiveRecord::Base
  has_many :users
end

class User < ActiveRecord::Base
  belongs_to :topic
end

100.times do
  User.create!(attributes)
end

users = User.first(50)

Topic.create!(title: 'This is a topic', users: users)

Benchmark.ips do |x|
  x.config(time: 10, warmup: 5)

  x.report("preload") do
    User.includes(:topic).all.to_a
  end
end
```

Before

```
Calculating -------------------------------------
             preload    26.000  i/100ms
-------------------------------------------------
             preload    265.347  (± 3.0%) i/s -      2.652k
```

After

```
Calculating -------------------------------------
             preload    39.000  i/100ms
-------------------------------------------------
             preload    406.053  (± 1.7%) i/s -      4.095k
```

It's done inside each test via assert_called_with or Kernel.expects

Currently the normalization only exists in `primary_key` shorthand. It
should be moved to `new_column_definition` to also affect to
`add_column` with primary key.

Currently implicit legacy primary key is compatible, but adding explicit
legacy primary key is not compatible. It should also be fixed.

Fixes #30664.

`change_column_{default,null,comment}` in mysql2 adapter are passing
`column.sql_type` as `type` to `change_column` to intend keeping
previous type. But `column_for` requires extra query, so use passing
`nil` to `type` explicitly in the internal for the purpose.