Merge pull request #13583 from arthurnn/mem_cache_store_fix

mem_cache_store requires dalli, so only accept dalli/client

activesupport/CHANGELOG.md

+*   MemCacheStore should only accept a Dalli::Client, or create one.
+
+    *arthurnn*
+
 *   Don't lazy load the `tzinfo` library as it causes problems on Windows.
 
     Fixes #13553

activesupport/lib/active_support/cache/mem_cache_store.rb

@@ -41,17 +41,15 @@ def self.build_mem_cache(*addresses)
       #
       # If no addresses are specified, then MemCacheStore will connect to
       # localhost port 11211 (the default memcached port).
-      #
-      # Instead of addresses one can pass in a MemCache-like object. For example:
-      #
-      #   require 'memcached' # gem install memcached; uses C bindings to libmemcached
-      #   ActiveSupport::Cache::MemCacheStore.new(Memcached::Rails.new("localhost:11211"))
       def initialize(*addresses)
         addresses = addresses.flatten
         options = addresses.extract_options!
         super(options)
 
-        if addresses.first.respond_to?(:get)
+        unless [String, Dalli::Client, NilClass].include?(addresses.first.class)
+          raise ArgumentError, "First argument must be an empty array, an array of hosts or a Dalli::Client instance."
+        end
+        if addresses.first.is_a?(Dalli::Client)
           @data = addresses.first
         else
           mem_cache_options = options.dup

activesupport/test/caching_test.rb

@@ -110,12 +110,12 @@ def test_mem_cache_fragment_cache_store_with_given_mem_cache
     assert_kind_of(ActiveSupport::Cache::MemCacheStore, store)
   end
 
-  def test_mem_cache_fragment_cache_store_with_given_mem_cache_like_object
+  def test_mem_cache_fragment_cache_store_with_not_dalli_client
     Dalli::Client.expects(:new).never
     memcache = Object.new
-    def memcache.get() true end
-    store = ActiveSupport::Cache.lookup_store :mem_cache_store, memcache
-    assert_kind_of(ActiveSupport::Cache::MemCacheStore, store)
+    assert_raises(ArgumentError) do
+      ActiveSupport::Cache.lookup_store :mem_cache_store, memcache
+    end
   end
 
   def test_mem_cache_fragment_cache_store_with_multiple_servers