Ensure cache directory exists

Fixes rails#244

lib/sprockets/cache/file_store.rb

@@ -6,14 +6,11 @@ module Sprockets
   module Cache
     # A simple file system cache store.
     #
-    #     environment.cache = Sprockets::Cache::FileStore.new("tmp/sprockets")
+    #     environment.cache = Sprockets::Cache::FileStore.new("/tmp")
     #
     class FileStore
       def initialize(root)
         @root = Pathname.new(root)
-
-        # Ensure directory exists
-        FileUtils.mkdir_p @root
       end
 
       # Lookup value in cache
@@ -24,6 +21,9 @@ def [](key)
 
       # Save value to cache
       def []=(key, value)
+        # Ensure directory exists
+        FileUtils.mkdir_p @root.join(key).dirname
+
         @root.join(key).open('w') { |f| Marshal.dump(value, f)}
         value
       end

test/test_caching.rb

@@ -180,3 +180,33 @@ def setup
     end
   end
 end
+
+require 'tmpdir'
+
+class TestFileStore < Sprockets::TestCase
+  def setup
+    @cache = Sprockets::Cache::FileStore.new(Dir::tmpdir)
+
+    @env1 = Sprockets::Environment.new(fixture_path('default')) do |env|
+      env.append_path(".")
+      env.cache = @cache
+    end
+
+    @env2 = Sprockets::Environment.new(fixture_path('symlink')) do |env|
+      env.append_path(".")
+      env.cache = @cache
+    end
+  end
+
+  test "shared cache objects are eql" do
+    asset1 = @env1['gallery.js']
+    asset2 = @env2['gallery.js']
+
+    assert asset1
+    assert asset2
+
+    assert asset1.eql?(asset2)
+    assert asset2.eql?(asset1)
+    assert !asset1.equal?(asset2)
+  end
+end