pass the key to the block in cache.fetch on misses

activesupport/lib/active_support/cache.rb

@@ -182,10 +182,10 @@ def self.instrument
       # the cache with the given key, then that data is returned.
       #
       # If there is no such data in the cache (a cache miss), then +nil+ will be
-      # returned. However, if a block has been passed, that block will be run
-      # in the event of a cache miss. The return value of the block will be
-      # written to the cache under the given cache key, and that return value
-      # will be returned.
+      # returned. However, if a block has been passed, that block will be passed
+      # the key and executed in the event of a cache miss. The return value of the
+      # block will be written to the cache under the given cache key, and that
+      # return value will be returned.
       #
       #   cache.write('today', 'Monday')
       #   cache.fetch('today')  # => "Monday"
@@ -300,7 +300,7 @@ def fetch(name, options = nil)
             entry.value
           else
             result = instrument(:generate, name, options) do |payload|
-              yield
+              yield(name)
             end
             write(name, result, options)
             result

activesupport/test/caching_test.rb

@@ -83,7 +83,7 @@ def test_expand_cache_key_of_false
   def test_expand_cache_key_of_true
     assert_equal 'true', ActiveSupport::Cache.expand_cache_key(true)
   end
-  
+
   def test_expand_cache_key_of_array_like_object
     assert_equal 'foo/bar/baz', ActiveSupport::Cache.expand_cache_key(%w{foo bar baz}.to_enum)
   end
@@ -197,6 +197,11 @@ def test_fetch_with_cache_miss
     assert_equal 'baz', @cache.fetch('foo') { 'baz' }
   end
 
+  def test_fetch_with_cache_miss_passes_key_to_block
+    @cache.expects(:write).with('foo', 3, @cache.options)
+    assert_equal 3, @cache.fetch('foo') { |key| key.length }
+  end
+
   def test_fetch_with_forced_cache_miss
     @cache.write('foo', 'bar')
     @cache.expects(:read).never
@@ -594,7 +599,7 @@ def test_key_transformation_with_pathname
     assert_equal "views/index?id=1", @cache_with_pathname.send(:file_path_key, key)
   end
 
-  # Test that generated cache keys are short enough to have Tempfile stuff added to them and 
+  # Test that generated cache keys are short enough to have Tempfile stuff added to them and
   # remain valid
   def test_filename_max_size
     key = "#{'A' * ActiveSupport::Cache::FileStore::FILENAME_MAX_SIZE}"