we already have a request, so we should use the methods on the request
to access the path info information

Creates fewer request objects and helps to abstract away from internals

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.