try to remove dependencies on `@env` so we can have more flexible
internals

Remove test helper method to inside test method

Another place to use a request object in NullSessionHash

Remove a link to the site that seems to be gone. [ci skip]

Added docs for CollectionProxy#take 

Followup to #20637.

Remove `MigrationTest#connection` and write `ActiveRecord::Base.connection`
directly to test, because `MigrationTest#connection` is only used in
`test_migration_instance_has_connection`.

May be missed in 5fe14163 commit
Also fixes the broken build

fix syntax error in strip_links example [ci skip]

can not use double quotes in double quoted string without escape

Remove not used a block argument (`&block`)

[ci skip] Add style guide about comma

This commit allows us to use one request object rather than allocating
multiple request objects to deal with the session.

We're going to implement storing env values differently in the future,
so let's disconnect these methods from the instance variables

we're already doing this with a bunch of other header data.

we have a method that knows how to get rack.input, so lets use that.

We need to abstract the internals of the request object away from this
instance variable so that the values for `@env` can be calculated in a
different way.

Rack changed their status codes to IETF RFC 7231

Since none of the action pack tests failed without this conditional it
didn't seem necessary. This fixes the build because it correctly returns
a 404 instead of a 500 for the asset routes test.

Test that was failing was in the `assets_test.rb` file and was the test
named `test_assets_routes_are_not_drawn_when_compilation_is_disabled`.

This refactoring moves the controller class name that was on the route
set to the request. The purpose of this refactoring is for changes we
need to move controller tests to integration tests, mainly being able to
access the controller on the request instead of having to go through
the router.

[Eileen M. Uchitelle & Aaron Patterson]

[skip ci] Debugging Rails Guide fixes

- Fixes:

"we want go deep" -> "we won't go deep"

"to next next line" -> "to the next line"

- Minor improvements in clarity and grammar.

Cheers :)

we want to go through methods to access `env` because in the future that
ivar may not be available, or may be calculated lazily

now the parameter filter doesn't need to know about the env hash in
these two methds.

Now the Headers internals don't depend on the env hash.

This prevents external mutations from impacting the internals of the
request or the Header object.

this reduces the API footprint for the env hash so that we can be more
flexible when changing API in the future

This allows us to avoid calling `env_name` twice.

duping the request will dup it's underlying env hash.

Several changes were made in #21110 which I am strongly opposed to.
(this is what I get for going on vacation. :trollface:) No type should
be introduced into the generic `ActiveRecord::Type` namespace, and
*certainly* should not be registered into the registry unconstrained
unless it is supported by *all* adapters (which basically means that it
was specified in the ANSI SQL standard).

I do not think `# :nodoc:` ing the type is sufficient, as it still makes
the code of Rails itself very unclear as to what the role of that class
is. While I would argue that this shouldn't even be a super class, and
that MySql and PG's JSON types are only superficially duplicated (they
might look the same but will change for different reasons in the
future).

However, I don't feel strongly enough about it as a point of contention
(and the biggest cost of harming the blameability has already occured),
so I simply moved the superclass into a namespace where its role is
absolutely clear.

After this change, `attribute :foo, :json` will once again work with
MySQL and PG, but not with Sqlite3 or any third party adapters.

Unresolved questions
--------------------

The types that and adapter publishes (at least those are unique to that
adapter, and not adding additional behavior like `MysqlString` should
probably be part of the adapter's public API. Should we standardize the
namespace for these, and document them?

`ActiveSupport::Dependencies.constantize(const_name)` calls
`Reference.new` which is defined as
`ActiveSupport::Dependencies.constantize(const_name)` meaning this call
is already cached and we're doing caching that isn't necessary.