This is not true anymore, the image will be downloaded into a temporary
file in a streaming fashion.

ImageProcessing gem is a wrapper around MiniMagick and ruby-vips, and
implements an interface for common image resizing and processing. This
is the canonical image processing gem recommended in [Shrine], and
that's where it developed from. The initial implementation was extracted
from Refile, which also implements on-the-fly transformations.

Some features that ImageProcessing gem adds on top of MiniMagick:

  * resizing macros
    - #resize_to_limit
    - #resize_to_fit
    - #resize_to_fill
    - #resize_and_pad
  * automatic orientation
  * automatic thumbnail sharpening
  * avoids the complex and inefficient MiniMagick::Image class
  * will use "magick" instead of "convert" on ImageMagick 7

However, the biggest feature of the ImageProcessing gem is that it has
an alternative implementation that uses libvips. Libvips is an
alternative to ImageMagick that can process images very rapidly (we've
seen up 10x faster than ImageMagick).

What's great is that the ImageProcessing gem provides the same interface
for both implementations. The macros are named the same, and the libvips
implementation does auto orientation and thumbnail sharpening as well;
only the operations/options specific to ImageMagick/libvips differ. The
integration provided by this PR should work for both implementations.

The plan is to introduce the ImageProcessing backend in Rails 6.0 as the
default backend and deprecate the MiniMagick backend, then in Rails 6.1
remove the MiniMagick backend.

The JavaScript component expects a bare response.

Fixes #32365

VariantsController has been merged to RepresentationsController, this
PR fixes outdated references to VariantsController in ActiveStorage documentation.

Trying to pass the current request down to the service so that it can
create full urls instead of paths makes the API messy so use a model
based on ActiveSupport::CurrentAttributes to provide the current host
to services that need it (primarily the disk service).

Before it was possible to for example use the direct upload controller
without using the site.

Addresses rails/rails#32247

Add test that checks identify and analyze work in correct order

Break out direct upload test helper

Review changes for direct-upload test helper

If an explicit AWS key pair and/or region is not provided in
config/storage.yml, attempt to use environment variables, shared
credentials, or IAM role credentials. Order of precedence is
determined by the AWS SDK[1].

[1]: https://docs.aws.amazon.com/sdk-for-ruby/v3/developer-guide/setup-config.html

We only add the header when releasing to avoid some conflicts.

[ci skip]

The Active Storage service for Azure Storage has an option called `path`
that is ambiguous in meaning. It needs to be set to the primary blob
storage endpoint but that can be determined from the blobs client anyway.

To simplify the configuration this commit removes the `path` option and
gets the endpoint from the blobs client instead.

Closes #32225.

mutool is licensed under the Affero GPL, which has strict distribution requirements.

Poppler is licensed under the more liberal GPL, making it a good alternative for those who can't use mutool.

Since we started clearing the client-side blob's type in e0867b36, we no longer need to set a blank Content-Type header before issuing the direct upload request. Fixes that Safari 9 would combine the blank Content-Type header with the blank blob type to produce a Content-Type header containing a single comma, invalidating the request.

[Matt Jones & George Claghorn]

Fixes #32129.

Since ActiveStorage::Blob::Representable unifies the idea of previews and
variants under one roof as representation, we may as well have the
controllers follow suit.

Thus ActiveStorage::RepresenationsController enters the fray. I've copied
the old tests for both previews and variants and unified those as well.

Ruby 2.4+ provides `Hash#compact` and `Hash#compact!` natively,
so `active_support/core_ext/hash/compact` is no longer necessary.

Prevent older versions of Chrome from appending a Content-Type header containing the Blob type, rendering the request invalid if we intend not to provide a Content-Type. This behavior was observed in Chrome 58.

Fix customizing the download Content-Type for a directly-uploaded blob via a signed URL. See e8286ee2.

Remove railties' changelog added by 7340596d
since it was backported to `5-2-stable` via ac99916f

Remove activesupport's changelog added by 1077ae96
since it was backported to `5-2-stable` via a2b97e4f

Remove activesupport's changelog added by 0d41a76d
since it was backported to `5-2-stable` via cdce6a70

Remove activestorage's changelog added by d57c52a3
since it was backported to `5-2-stable` via 5292cdf5

Follow up c113bdc9

`to_prepare` callbacks are run during initialization; using one here
meant that `ActiveStorage::Blob` would be loaded when the app boots,
which would in turn load `ActiveRecord::Base`.

By using a lazy load hook to configure `ActiveStorage::Blob` instead,
we can avoid loading `ActiveRecord::Base` unnecessarily.

Closes #32096.

Only us-east-1 gives URLs like bucket.s3.amazonaws.com whereas other
regions have URLs like s3-eu-west-1.amazonaws.com/ubxd-rails