Merge pull request #24577 from mechanicles/fix-fetch-cache-miss

Fix forced cache miss for fetch when called without a block.

3 files changed, 33 insertions, 2 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index b2ab5ffcbe..bcf3b10208 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   `Cache#fetch(key, force: true)` forces a cache miss, so it must be called
+    with a block to provide a new value to cache. Fetching with `force: true`
+    but without a block now raises ArgumentError.
+
+        cache.fetch('key', force: true) # => ArgumentError
+
+    *Santosh Wadghule*
+
 *   `ActiveSupport::Duration` supports weeks and hours.
 
         [1.hour.inspect, 1.hour.value, 1.hour.parts]
diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb
index 914390eef1..bc114e0785 100644
--- a/activesupport/lib/active_support/cache.rb
+++ b/activesupport/lib/active_support/cache.rb
@@ -198,10 +198,17 @@ module ActiveSupport
       #   cache.fetch('city')   # => "Duckburgh"
       #
       # You may also specify additional options via the +options+ argument.
-      # Setting <tt>force: true</tt> will force a cache miss:
+      # Setting <tt>force: true</tt> forces a cache "miss," meaning we treat
+      # the cache value as missing even if it's present. Passing a block is
+      # required when `force` is true so this always results in a cache write.
       #
       #   cache.write('today', 'Monday')
-      #   cache.fetch('today', force: true)  # => nil
+      #   cache.fetch('today', force: true) { 'Tuesday' } # => 'Tuesday'
+      #   cache.fetch('today', force: true) # => ArgumentError
+      #
+      # The `:force` option is useful when you're calling some other method to
+      # ask whether you should force a cache write. Otherwise, it's clearer to
+      # just call `Cache#write`.
       #
       # Setting <tt>:compress</tt> will store a large cache entry set by the call
       # in a compressed format.
@@ -292,6 +299,8 @@ module ActiveSupport
           else
             save_block_result_to_cache(name, options) { |_name| yield _name }
           end
+        elsif options && options[:force]
+          raise ArgumentError, 'Missing block: Calling `Cache#fetch` with `force: true` requires a block.'
         else
           read(name, options)
         end
diff --git a/activesupport/test/caching_test.rb b/activesupport/test/caching_test.rb
index 9e744afb2b..ec7d028d7e 100644
--- a/activesupport/test/caching_test.rb
+++ b/activesupport/test/caching_test.rb
@@ -266,6 +266,20 @@ module CacheStoreBehavior
     end
   end
 
+  def test_fetch_with_forced_cache_miss_with_block
+    @cache.write('foo', 'bar')
+    assert_equal 'foo_bar', @cache.fetch('foo', force: true) { 'foo_bar' }
+  end
+
+  def test_fetch_with_forced_cache_miss_without_block
+    @cache.write('foo', 'bar')
+    assert_raises(ArgumentError) do
+      @cache.fetch('foo', force: true)
+    end
+
+    assert_equal 'bar', @cache.read('foo')
+  end
+
   def test_should_read_and_write_hash
     assert @cache.write('foo', {:a => "b"})
     assert_equal({:a => "b"}, @cache.read('foo'))