user form with instead of form for in scaffold generator

Fix extension method with dirty target in has_many associations

Add `app:update` task to engines

Delegate `uniq` to `records`

Fix `select_all` with legacy `binds`

Occasionally we update the file generated by engine.
Therefore, I think that there is a task for updating as well as
application in the engine, it is convenient for updating.

Fix `warning: character class has duplicated range`

Evaluate the default block only when necessary

Fix changelog entry about transaction error classes [ci skip]

`ActiveRecord::TransactionSerializationError` was introduces in #25093.
However, refactored in #25107, `TransactionSerializationError` is gone.

This fixes the following warnings:

```
railties/test/generators/encrypted_secrets_generator_test.rb:15: warning: character class has duplicated range: /[\w\d]+/
railties/test/generators/encrypted_secrets_generator_test.rb:18: warning: character class has duplicated range: /production:\n#  external_api_key: [\w\d]+/
railties/test/generators/encrypted_secrets_generator_test.rb:19: warning: character class has duplicated range: /production:\n#  external_api_key: [\w\d]+/
```

Correctly check whether key is defined in configuration

Follow up of #28453.

Remove stray back-end from ActiveJob Basics guide

Minor grammar fixes for Rails 5.1 release notes

It can not check correctly with `defined?`

```ruby
irb(main):001:0> Rails.application.config.active_record
=> {:maintain_test_schema=>true, :belongs_to_required_by_default=>true}
irb(main):002:0> defined?(Rails.application.config.active_record)
=> nil
```

Follow up to #28469

The hyphenated form "back-end" only appears once in this guide; elsewhere, the un-hyphenated form "backend" is used consistently.

[ci skip]

[ci skip]

[ci skip]

[ci skip]

Fixing tons of grammar, etc.

[ci skip]

Move new CHANGELOG entry to the top [ci skip]

Improve Caching with Rails Guides [ci skip]

Track the version-compatible config settings inside railties

Since b644964b `ActiveRecord::Relation` includes `Enumerable` so
delegating `collect`, `all?`, and `include?` are also unneeded.
`collect` without block returns `Enumerable` without preloading by that.
We should use `load` rather than `collect` for force loading.

This fixes CI failure due to 48f3be8c.

`Enumerable#uniq` was introduced since Ruby 2.4. We should delegate
`uniq` to `records` explicitly.

And since b644964b `ActiveRecord::Relation` includes `Enumerable` so
delegating `map` is unneeded.

Action View overrides `url_for` in the view context to render paths by
default when using `url_for` and this means that direct route helpers
don't get the full url when called with the url suffix. To fix this
always call the original `url_for`.

Instead of forcing new applications to carry an initializer that just
switches things to what their default "should" be, we can handle it
internally.

The initializer is then only used by upgraders: it shows what the new
default would be (commented out), while their upgraded application
continues to operate as it did before.

Under this model, a multiply-upgraded application could accumulate
several new_framework_defaults_*.rb files, for each release series it
has traversed. A given release series only needs to generate the latest,
though, because we don't support `rails app:upgrade` while skipping
releases.

Adds the "Caching in Development" section to
demonstrate usage of the dev:cache task in development mode.

Also, makes a small grammatical correction in section 2.4.

Allow order to be given expressions as hash keys

Drop comments from structure.sql in postgresql

[ci skip]

Add first draft of release notes for Rails 5.1 🎉

This was causing an infinity loop since it was delegating to `all` and
all delegating back to this module.

Not all requirements can be expressed in terms of polymorphic url
options so add a `route_for` method that allows calling another
direct route (or regular named route) which a set of arguments, e.g:

    resources :buckets

    direct :recordable do |recording|
      route_for(:bucket, recording.bucket)
    end

    direct :threadable do |threadable|
      route_for(:recordable, threadable.parent)
    end

This maintains the context of the original caller, e.g.

    threadable_path(threadable) # => /buckets/1
    threadable_url(threadable)  # => http://example.com/buckets/1

Pass options to `driven_by`