Change #cache_storage to use #storage by default to avoid confusion

Most users won't expect that they must be configured separately,
like said in #2353. But we preserve ability to set cache_storage explicitly,
because there can be a case which gets benefit from it.
(e.g. For an application which utilizes multiple servers but does not
need caches to be persisted across requests, using :fog for storage and
:file for cache_storage results in smaller overhead)

lib/carrierwave/uploader/cache.rb

@@ -64,7 +64,7 @@ module ClassMethods
         # It's recommended that you keep cache files in one place only.
         #
         def clean_cached_files!(seconds=60*60*24)
-          cache_storage.new(CarrierWave::Uploader::Base.new).clean_cache!(seconds)
+          (cache_storage || storage).new(CarrierWave::Uploader::Base.new).clean_cache!(seconds)
         end
       end
 
@@ -208,7 +208,7 @@ def original_filename=(filename)
       end
 
       def cache_storage
-        @cache_storage ||= self.class.cache_storage.new(self)
+        @cache_storage ||= (self.class.cache_storage || self.class.storage).new(self)
       end
     end # Cache
   end # Uploader

lib/carrierwave/uploader/configuration.rb

@@ -110,8 +110,8 @@ def storage(storage = nil)
         #     cache_storage CarrierWave::Storage::File
         #     cache_storage MyCustomStorageEngine
         #
-        def cache_storage(storage = nil)
-          if storage
+        def cache_storage(storage = false)
+          unless storage == false
             self._cache_storage = storage.is_a?(Symbol) ? eval(storage_engines[storage]) : storage
           end
           _cache_storage
@@ -186,7 +186,7 @@ def reset_config
               :fog  => "CarrierWave::Storage::Fog"
             }
             config.storage = :file
-            config.cache_storage = :file
+            config.cache_storage = nil
             config.fog_attributes = {}
             config.fog_credentials = {}
             config.fog_public = true

spec/uploader/configuration_spec.rb

@@ -1,5 +1,4 @@
 require 'spec_helper'
-require 'carrierwave/storage/fog'
 
 describe CarrierWave do
   describe '.configure' do
@@ -81,6 +80,21 @@
     end
   end
 
+  describe ".cache_storage" do
+    it "returns the same storage as given by #storage" do
+      uploader_class.storage :file
+      expect(uploader_class.new.send(:cache_storage)).to be_a(CarrierWave::Storage::File)
+      uploader_class.storage :fog
+      expect(uploader_class.new.send(:cache_storage)).to be_a(CarrierWave::Storage::Fog)
+    end
+
+    it "can be explicitly set" do
+      uploader_class.storage :fog
+      uploader_class.cache_storage :file
+      expect(uploader_class.new.send(:cache_storage)).to be_a(CarrierWave::Storage::File)
+    end
+  end
+
   describe '.add_config' do
     before do
       uploader_class.add_config :foo_bar

spec/uploader/versions_spec.rb

@@ -308,6 +308,7 @@ def move_to_cache
 
     describe '#store!' do
       before do
+        @uploader_class.cache_storage = :file
         @uploader_class.storage = mock_storage('base')
         @uploader_class.version(:thumb).storage = mock_storage('thumb')
         @uploader_class.version(:preview).storage = mock_storage('preview')
@@ -490,6 +491,7 @@ def move_to_cache
 
     describe '#remove!' do
       before do
+        @uploader_class.cache_storage = :file
         @uploader_class.storage = mock_storage('base')
         @uploader_class.version(:thumb).storage = mock_storage('thumb')