https://github.com/rails/rails/blob/e64a83cdbd3ce836f3339c600c1006b20c23d8fd/activerecord/test/cases/relation/merging_test.rb#L80-91

rather than allocating a new Relation, just make the AST directly

Conflicts:
	activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb

This fixes broken `rake test_sqlite3_mem` suite for Active Record.
The problem is that that the old database with the schema is lost
when establishing a new connection. Upon reconnting we are left
with a blank database and tests down the line start failing.

sqlite >= 3.8.0 supports partial indexes

Active Record's subclass_from_attributes shouldn't assume :type is for STI unless there is a type column.

The `subclass_from_attrs` method is called even if the column specified by
the `inheritance_column` setting doesn't exist. This prevents setting associations
via the attributes hash if the association name clashes with the value of the setting,
typically `:type`. This worked previously in Rails 3.2.

Example:

    class Conversation < ActiveRecord::Base
      enum status: [ :active, :archived ]
    end

Before:

    Conversation::STATUS # => { "active" => 0, "archived" => 1 }

After:

    Conversation.statuses # => { "active" => 0, "archived" => 1 }

Single quotes for controller generated routes. This is more consistent with all other Rails generated code.

Fix fields_for documentation with index option [ci skip]

- fields_for documentation with index option was wrong.
- It does not work with passing model as it is.
- Changed the example by passing id of the address object.
- Fixes #13125.

[ci skip] Grammar correction

Set NameError#name

[ci skip] Added alias to CSRF

Write routes in route.rb with single quotes

    get 'welcome/index'

instead of

    get "welcome/index"

It's not public API, but is not private scoped.

"serie" => "series"

More to come.

Favor canonical environment variables for secrets

Prefixing an environment variable with `RAILS_` should be used when there is otherwise a conflict, such as `RAILS_ENV` or if it is being used for a very Rails specific value.

If we remove the prefix of `RAILS_` in the case of `RAILS_SECRET_KEY_BASE` then we can push for a pseudo standard among other frameworks that will accept a common environment key `SECRET_KEY_BASE` to keep your app secure. This is beneficial for containerized deployments such as docker, Heroku, etc. So that the container need to know one less thing about your app (it can just set it no-matter what language or framework you are using). 

This change also allows the defaults to be consistent with the way the secret key is accessed so `secrets.secret_key_base` is aliased to `SECRET_KEY_BASE` instead of `RAILS_SECRET_KEY_BASE`.

removed extra comma [ci skip]

This prevents Rails from assigning meaningless log levels to third
party loggers like log4r. If `Rails.logger` is not `kind_of?(::Logger)`
we simply assign the `config.log_level` as is.

This bug was introduced by #11665.

Updated Changelog to reflect removal of :dependent => :restrict

Based on https://github.com/rails/rails/issues/2502, the option has
been removed.

[JRuby] Fix incorrect RUBY_ENGINE value 

This Adds helpers(jruby_skip & rbx_skip). In Future, Plan is to use
these helpers instead of calls directly to
RUBY_ENGINE/RbConfig/JRUBY_VERSION