deprecation warnings with sprockets 3.7.0

[maia]

sass-rails-5.0.5 throws deprecation warnings when using sprockets 3.7.0:

DEPRECATION WARNING: Sprockets method `register_engine` is deprecated.
Please register a mime type using `register_mime_type` then
use `register_compressor` or `register_transformer`.
https://github.com/rails/sprockets/blob/master/guides/extending_sprockets.md#supporting-all-versions-of-sprockets-in-processors
(called from block (2 levels) in <class:Railtie> at /…/gems/sass-rails-5.0.5/lib/sass/rails/railtie.rb:57)
DEPRECATION WARNING: Sprockets method `register_engine` is deprecated.
Please register a mime type using `register_mime_type` then
use `register_compressor` or `register_transformer`.
https://github.com/rails/sprockets/blob/master/guides/extending_sprockets.md#supporting-all-versions-of-sprockets-in-processors
(called from block (2 levels) in <class:Railtie> at /…/gems/sass-rails-5.0.5/lib/sass/rails/railtie.rb:58)

[rob-race]

Quick fix for me(for now) was...

gem 'sprockets', '3.6.3'

[jaredbeck]

Same warning in js-routes (railsware/js-routes#201) I suspect a lot of sprockets extensions will be fixing this in similar ways and may benefit from each other's work.

[kapso]

Seeing same warning in https://github.com/ai/autoprefixer-rails

[rafaelfranca]

cc @schneems

[schneems]

Working on a PR.

[maia]

@schneems Thanks a lot for solving the issue with the release of 5.0.6!

[schneems]

Thanks all for chiming in. I added some docs to Sprockets guides on master to show how to register an processor across Sprockets 2, 3, and 4. Link: https://github.com/rails/sprockets/blob/master/guides/extending_sprockets.md#registering-all-versions-of-sprockets-in-processors

I also re-wrote the guide to be easier to reference, put the most relevant examples at the top of the sections and added a table of contents at the top. Please take a look and if you have something to add or ways you think the docs could be better open an issue and we can talk about it. I want the process of maintaining Sprockets extensions to be as easy as possible, I'm hoping the docs can smooth out rough edges and cut down on guessing how to write a sprockets plugin.

If you're working on getting rid of deprecations in your own library and having problems, ping me on a pull request.