Accept variation keys in #preview and #variant

activestorage/app/models/active_storage/blob.rb

@@ -124,7 +124,7 @@ def text?
   # This will create a URL for that specific blob with that specific variant, which the ActiveStorage::VariantsController
   # can then produce on-demand.
   def variant(transformations)
-    ActiveStorage::Variant.new(self, ActiveStorage::Variation.new(transformations))
+    ActiveStorage::Variant.new(self, ActiveStorage::Variation.wrap(transformations))
   end
 
 
@@ -144,7 +144,7 @@ def variant(transformations)
   # whether a blob is accepted by any previewer, call ActiveStorage::Blob#previewable?.
   def preview(transformations)
     if previewable?
-      ActiveStorage::Preview.new(self, ActiveStorage::Variation.new(transformations))
+      ActiveStorage::Preview.new(self, ActiveStorage::Variation.wrap(transformations))
     else
       raise UnpreviewableError
     end

activestorage/app/models/active_storage/variation.rb

@@ -13,16 +13,21 @@ class ActiveStorage::Variation
   attr_reader :transformations
 
   class << self
-    def wrap(variation_or_key)
-      case variation_or_key
+    # Returns a Variation instance based on the given variator. If the variator is a Variation, it is
+    # returned unmodified. If it is a String, it is passed to ActiveStorage::Variation.decode. Otherwise,
+    # it is assumed to be a transformations Hash and is passed directly to the constructor.
+    def wrap(variator)
+      case variator
       when self
-        variation_or_key
+        variator
+      when String
+        decode variator
       else
-        decode variation_or_key
+        new variator
       end
     end
 
-    # Returns a variation instance with the transformations that were encoded by +encode+.
+    # Returns a Variation instance with the transformations that were encoded by +encode+.
     def decode(key)
       new ActiveStorage.verifier.verify(key, purpose: :variation)
     end