MySQL does not support partial index. And, the create index algorithm in
create table can not be specified.

Mailer preview now uses `url_for` to fix links to emails for apps runnin...

 Removed `assigns` from functional_test templates

Dump indexes in `create_table` instead of `add_index`

Actionview image tag size option override

Merge pull request #17824 from yuki24/change-record-not-saved-and-not-destroyed-to-include-error-msg

AR::RecordNotSaved & RecordNotDestroyed from save!/destroy! should include an error message

Correctly dump `:options` on `create_table` for MySQL

Move PostgreSQL specific schema to postgresql_specific_schema.rb

PostgreSQL: `:collation` support for string and text columns

Use ruby 1.9 lambda syntax in documentations [ci skip]

Changed 'ask the rubyonrails-talk mailing list.' to 'ask it on the rubyo...

Change the `visit_AddColumn` visiblity for the internal API

See #19498

The implementations seems to not be interested to remove the warnings so
enabling them we are just making harder to read the outputs

add upgrade note for breaking habtm change in 3.2 -> 4.0

ActiveJob: Stop using Que's named queues.

Missing `:bigint` [ci skip]

Example:

    create_table :foos do |t|
      t.string :string_en, collation: 'en_US.UTF-8'
      t.text   :text_ja,   collation: 'ja_JP.UTF-8'
    end

Some databases like MySQL allow defining collation charset for specific
columns.

Move comment about microseconds [ci skip]

gem 'mysql2', '~> 0.3.18'

Follow up #18914.

`:nodoc:` postgresql's change_column

If the adapter supports indexes in create table, generated SQL is
slightly more efficient.

Its nodoc'ed for the other implementations, and doc'ed in the base
class, just like the other change_column* methods.

The microseconds handling was already moved to `Quoting#quoted_date`.

[ci skip] Uniquiness with scope can have one or more arguments

:nodoc: change_column_null in the implmenting adapters

Remove unused require

`change_column_null` is doc'ed only in
ActiveRecord::ConnectionAdapters::SchemaStatements, so it would make
sense to :nodoc: it elsewhere.