Bundler 1.14.5 moved to lazily loading 'rubygems/spec_fetcher' which
revealed some missing requires from the JSON encoding test file.

Preload to_datetime before freezing a TimeWithZone instance

remove needless extension from system test example [ci skip]

[doc] Fix wrong class name in testing.md

As the specified command is `rails g system_test articles`, the generated class name
is `ArticlesTest`, not `UsersTest`

Allow 3-level DB configs to group connections by environment

Add CHANGELOG entry for #27384 and #27762

Use double quoted strings, come down hard on some typos.

Implement custom url helpers and polymorphic mapping

[Arthur Nogueira Neves & Matthew Draper]

[ci skip]

The column information for the testings table was being cached
so clear the cache in the test teardown.

[ci skip]

[ci skip]

[ci skip]

For applications that are upgrading or applications that are choosing to
skip system testing Capbyara will not be available. SystemTestCase and
friends shoud only be loaded if Capbyara is defined.

Fixes #28094

Use a separate method called `resolve` for the custom polymorphic
mapping to clarify the API.

Using `undef_method` means that when a route is removed any other
implementations of that method in the ancestor chain are inaccessible
so instead use `remove_method` which restores access to the ancestor.

Allow the use of `direct` to specify custom mappings for polymorphic_url, e.g:

  resource :basket
  direct(class: "Basket") { [:basket] }

This will then generate the following:

  >> link_to "Basket", @basket
  => <a href="/basket">Basket</a>

More importantly it will generate the correct url when used with `form_for`.

Fixes #1769.

Allow the definition of custom url helpers that will be available
automatically wherever standard url helpers are available. The
current solution is to create helper methods in ApplicationHelper
or some other helper module and this isn't a great solution since
the url helper module can be called directly or included in another
class which doesn't include the normal helper modules.

Reference #22512.

The singleton url_for on Rails.application.routes.url_helpers isn't the
same as the url_for you get when you include the module in your class as
the latter has support for polymorphic style routes, etc. whereas the
former accepts only a hash and is the underlying implementation defined
on ActionDispatch::Routing::RouteSet.

This commit changes the singleton method to call through a proxy instance
so that it gets the full range of features specified in the documentation
for url_for.

Fix `define_attribute_method` with Symbol in AR

This issue is only appear when you try to call `define_attribute_method`
and passing a symbol in Active Record. It does not appear in isolation
in Active Model itself.

Before this patch, when you run `User.define_attribute_method :foo`, you
will get:

    NoMethodError: undefined method `unpack' for :foo:Symbol
        from activerecord/lib/active_record/attribute_methods/read.rb:28:in `define_method_attribute'
        from activerecord/lib/active_record/attribute_methods/primary_key.rb:61:in `define_method_attribute'
        from activemodel/lib/active_model/attribute_methods.rb:292:in `block in define_attribute_method'
        from activemodel/lib/active_model/attribute_methods.rb:285:in `each'
        from activemodel/lib/active_model/attribute_methods.rb:285:in `define_attribute_method'

This patch contains both a fix in Active Model and a test in Active
Record for this error.