I think we are better off leaving `sudo` outside of the documented
way of installing gems (`activerecord`, `actionpack`, …).

We don’t want newbies to think that `sudo` is required or, even worse, than
they actually have to type `[sudo] gem install`.

In most scenarios, `sudo` is not needed to install gems, and people who do
need it, probably already know about it.

What do you think? 😁

Now that master points at Rails 5, we might not need to explain how
things used to work in Rails 3. Or we might… up to you 😁

the module name was changed in 8e814a0a

The old `test_create_bang_returns_falsy_when_join_record_has_errors` had
a missleading name and was a duplicate of
`test_save_should_not_raise_exception_when_join_record_has_errors`.

Since it had an assertion on the return value I renamed it accordingly
and got rid of the duplicate test.

Its already doc'ed in
activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

Make sure that tests do not hardcode the default value.
For example `test_instantiation_doesnt_try_to_require_corresponding_file`
always restored the configuration to `true` regardless of what it's
original value was.

Extract a helper to make the global modification consistent across tests.

`exec_query` create `ActiveRecord::Result` instance. It is better to use
`select_value` instead of `exec_query` for performance.

`select_one` create `ActiveRecord::Result` instance. It is better to use
`select_rows` instead of `select_one` for performance.

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

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.

Follow up #18914.

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`.

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

When `AR::Base.save!` or `AR::Base.destroy!` is called and an exception
is raised, the exception doesn't have any error message or has a weird
message like `#<FailedBulb:0x0000000907b4b8>`. Give a better message so
we can easily understand why it's failing to save/destroy.

 - This method is used only by adapters to validate length of new index names.

 - Added documentation for index_name_exists? and rename_index.
 - Also changed rails to \Rails in documentation of
   allowed_index_name_length.

The `db:schema:cache:dump` rake task dumps the database schema structure
to `db/schema_cache.dump`. If this file is present, the schema details
are loaded into the currently checked out connection by a railtie while
Rails is booting, to avoid having to query the database for its schema.

The schema cache dump is only applied to the initial connection used to
boot the application though; other connections from the same pool are
created with an empty schema cache, and still have to load the structure
of each table directly from the database.

With this change, a copy of the schema cache is associated with the
connection pool and applied to connections as they are created.

Add a test-case to make sure that `create_table` with
a `foreign_key: true` and an adapter without foreign key support
does not blow up.

Motivated by #19794.

Originating from: https://github.com/rails/rails/commit/99a6f9e60ea55924b44f894a16f8de0162cf2702#commitcomment-10855210

This reverts commit 08ff4ccb, reversing
changes made to 6c9ed6db.

Caused by #17920.

Closes #19545.

This patch introduced regressions because initializers were no longer
loaded. Specifically missing inflections result in broken restores of
the database.

Also added reference for to_date, as it belongs historically.

follow up to 107526e8