From 921b877c2fd51cc0abdcf0ef6ca3528808047056 Mon Sep 17 00:00:00 2001
From: George Claghorn <george@basecamp.com>
Date: Tue, 2 Jan 2018 07:19:39 -0500
Subject: Restore support for the -layers transformation

---
 .../app/models/active_storage/variation.rb         |  28 ++++++++++-----------
 activestorage/test/fixtures/files/image.gif        | Bin 0 -> 2032 bytes
 activestorage/test/models/variant_test.rb          |   8 ++++++
 3 files changed, 22 insertions(+), 14 deletions(-)
 create mode 100644 activestorage/test/fixtures/files/image.gif

diff --git a/activestorage/app/models/active_storage/variation.rb b/activestorage/app/models/active_storage/variation.rb
index 2b599a4710..0046e6870b 100644
--- a/activestorage/app/models/active_storage/variation.rb
+++ b/activestorage/app/models/active_storage/variation.rb
@@ -46,15 +46,15 @@ class ActiveStorage::Variation
   # Accepts an open MiniMagick image instance, like what's returned by <tt>MiniMagick::Image.read(io)</tt>,
   # and performs the +transformations+ against it. The transformed image instance is then returned.
   def transform(image)
-    transformations.each do |(transformation_method, transformation_argument)|
-      if transformation_method.to_s == "combine_options"
-        image.combine_options do |combination|
-          transformation_argument.each do |(method, argument)|
-            pass_transform_argument(combination, method, argument)
+    transformations.each do |name, argument_or_subtransformations|
+      image.mogrify do |command|
+        if name.to_s == "combine_options"
+          argument_or_subtransformations.each do |subtransformation_name, subtransformation_argument|
+            pass_transform_argument(command, subtransformation_name, subtransformation_argument)
           end
+        else
+          pass_transform_argument(command, name, argument_or_subtransformations)
         end
-      else
-        pass_transform_argument(image, transformation_method, transformation_argument)
       end
     end
   end
@@ -65,15 +65,15 @@ class ActiveStorage::Variation
   end
 
   private
-    def eligible_argument?(argument)
-      argument.present? && argument != true
-    end
-
-    def pass_transform_argument(instance, method, argument)
+    def pass_transform_argument(command, method, argument)
       if eligible_argument?(argument)
-        instance.public_send(method, argument)
+        command.public_send(method, argument)
       else
-        instance.public_send(method)
+        command.public_send(method)
       end
     end
+
+    def eligible_argument?(argument)
+      argument.present? && argument != true
+    end
 end
diff --git a/activestorage/test/fixtures/files/image.gif b/activestorage/test/fixtures/files/image.gif
new file mode 100644
index 0000000000..90c05f671c
Binary files /dev/null and b/activestorage/test/fixtures/files/image.gif differ
diff --git a/activestorage/test/models/variant_test.rb b/activestorage/test/models/variant_test.rb
index 2a96dfb142..7157bfac3a 100644
--- a/activestorage/test/models/variant_test.rb
+++ b/activestorage/test/models/variant_test.rb
@@ -50,6 +50,14 @@ class ActiveStorage::VariantTest < ActiveSupport::TestCase
     assert_equal 20, image.height
   end
 
+  test "optimized variation of GIF blob" do
+    blob = create_file_blob(filename: "image.gif", content_type: "image/gif")
+
+    assert_nothing_raised do
+      blob.variant(layers: "Optimize").processed
+    end
+  end
+
   test "variation of invariable blob" do
     assert_raises ActiveStorage::Blob::InvariableError do
       create_file_blob(filename: "report.pdf", content_type: "application/pdf").variant(resize: "100x100")
-- 
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