Currently blank comment does not dump to `db/schema.rb`. But created it
even if specified blank.

All indentation was normalized by rubocop auto-correct at 80e66cc4.
But comments was still kept absolute position. This commit aligns
comments with method definitions for consistency.

Recently, the Rails team made an effort to keep the source code consistent, using Ruboco
(bb1ecdcc and below). Some of the case
statements were missed.

This changes the case statements' formatting and is consistent with changes
in 810dff7c and db63406c.

This reverts commit 3a1f6fe7.

This commit takes the code in a direction that I am looking to avoid.
The predicate builder should be purely concerned with AST construction
as it matters to methods like `where`. Things like case sensitivity
should continue to be handled elsewhere.

Strict mode controls how MySQL handles invalid or missing values in
data-change statements such as INSERT or UPDATE. If strict mode is not
in effect, MySQL inserts adjusted values for invalid or missing values
and produces warnings.

```ruby
  def test_mysql_not_null_defaults_non_strict
    using_strict(false) do
      with_mysql_not_null_table do |klass|
        record = klass.new
        assert_nil record.non_null_integer
        assert_nil record.non_null_string
        assert_nil record.non_null_text
        assert_nil record.non_null_blob

        record.save!
        record.reload

        assert_equal 0,  record.non_null_integer
        assert_equal "", record.non_null_string
        assert_equal "", record.non_null_text
        assert_equal "", record.non_null_blob
      end
    end
  end
```

It is inconsistent with other types that only text/blob defaults treated
as an empty string. This commit fixes the inconsistency.

Currently uniqueness validator is coupled with building Arel ASTs.
This commit extracts `PredicateBuilder::CaseSensitiveHandler` for
decouple the building Arel ASTs.

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

Related f27a932d, #25391.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

A `value` is only used for checking `value.nil?`. It is unnecessary if
immediately return when `value.nil?`.

`current_database` executes a query and `table_comment` is called to all
tables even if a table does not have a comment. Using `current_database`
increases extra queries.

[Rafael Mendonça França + Takeshi AKIMA]

Where appropriatei, prefer the more concise Regexp#match?,
String#include?, String#start_with?, or String#end_with?

`create_table_info_cache` is used for sharing `create_table_info` both
`table_options` and `foreign_keys`. But `foreign_keys` no longer uses
`create_table_info_cache` by #25307. No need caching anymore.

Fixes #25300.

Follow up of #20815.

```ruby
class CreatePeople < ActiveRecord::Migration[5.0]
  def change
    create_table :people do |t|
      t.integer :int
      t.bigint :bint
      t.text :txt
      t.binary :bin
    end
  end
end
```

Result.

In postgresql and sqlite3 adapters:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt"
    t.binary  "bin"
  end

end
```

In mysql2 adapter:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4" do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt",  limit: 65535
    t.binary  "bin",  limit: 65535
  end

end
```

After this patch:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4" do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt"
    t.binary  "bin"
  end

end
```

Ruby 2.4 unifies Fixnum and Bignum into Integer: https://bugs.ruby-lang.org/issues/12005

* Forward compat with new unified Integer class in Ruby 2.4+.
* Backward compat with separate Fixnum/Bignum in Ruby 2.2 & 2.3.
* Drops needless Fixnum distinction in docs, preferring Integer.

`schema_creation` is not public API.

https://github.com/rails/rails/blob/v5.0.0.beta4/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb#L121
https://github.com/rails/rails/blob/v5.0.0.beta4/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb#L78

Refactor of #22911.
Signed-off-by: NJeremy Daer <jeremydaer@gmail.com>

- Rename max to statement_limit
- Remove magic number 1000 from everywhere
- Defined StatementPool::DEFAULT_STATEMENT_LIMIT and started using it everywhere
Signed-off-by: NJeremy Daer <jeremydaer@gmail.com>

Adapters override `#supports_savepoints?` to return `true` if they
support transaction savepoints. Defaults to `false`.

`Arel::Visitors::VISITORS` was removed at https://github.com/rails/arel/pull/412.

* Switch to keyword args where we can without breaking compat.
* Use add_table_options! for :options, too.
* Some code polish.

Comments are specified in migrations, stored in database itself (in its schema),
and dumped into db/schema.rb file.

This allows to generate good documentation and explain columns and tables' purpose
to everyone from new developers to database administrators.

For PostgreSQL and MySQL only. SQLite does not support comments at the moment.

See docs for PostgreSQL: http://www.postgresql.org/docs/current/static/sql-comment.html
See docs for MySQL: http://dev.mysql.com/doc/refman/5.7/en/create-table.html

- Specify we want to run on latest stable ruby for mariadb

- change in runs of builds

Make mariadb? method publicly available

 Reason:
 - Its not publicly used method.
 - Exposing it makes an assumption that other adapters support it based on its usage - ActiveRecord::Base.connection.version

 [ci skip]

We support microsecond datetime precision for MySQL 5.6.4+. MariaDB has
supported it since 5.3.0, but even 10.x versions return a compatible
version string like `5.5.5-10.1.8-MariaDB-log` which we parse as 5.5.5,
before MySQL supported microsecond precision.

Specialize our version check to account for MariaDB to fix.