The main difference is that Sprockets 4.0 no longer tries to compile everything by default. This is good for us, because we can remove all our custom 'exclusion' logic which was working around the old sprockets 3.0 behavior.
The other big change is that lambdas can no longer be added to the `config.assets.precompile` array. Instead, we can do the necessary globs ourselves, and add the desired files manually.
A small patch is required to make ember-rails compatible. Since we plan to remove this dependency in the near future, I do not intend to upstream this change.
I have compared the `bin/rake assets:precompile` output before and after this change, and verified that all files are present.
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