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.
These routes are only used internally in Active Storage, and it seems
that there is no need for the user to directly use them.
Therefore, I think that routes should not be exposed to users.
Running `rubocop activestorage` before this commit resulted in 20 offenses.
This commit only fixes:
- Trailing whitespace detected
- Space inside } missing
- Put one space between the method name and the first argument.
The other offenses are left since they are intentional according to
@georgeclaghorn (https://github.com/rails/rails/pull/30061#issuecomment-319999190)
