Fixes to cache_for - all tests passing.

lib/rack/request.rb

@@ -480,8 +480,8 @@ def parseable_data?
         PARSEABLE_DATA_MEDIA_TYPES.include?(media_type)
       end
 
-      private def cache_for(key, validity_key, current_input)
-        if get_header(validity_key).equal?(current_input)
+      private def cache_for(key, validity_key, current_value)
+        if get_header(validity_key).equal?(current_value)
           if cache = get_header(key)
             if cache.key?(self.class)
               value = cache[self.class]
@@ -492,16 +492,19 @@ def parseable_data?
               end
             end
           end
-        else
-          set_header(validity_key, current_input)
         end
 
         unless cache
           set_header(key, cache = {})
         end
 
         cache.fetch(self.class) do
-          return cache[self.class] = yield(current_input)
+          value = yield(current_value)
+
+          # Only set this after generating the value, so that if an error or other cache depending on the same key, it will be invalidated correctly:
+          set_header(validity_key, current_value)
+
+          return cache[self.class] = value
         rescue => error
           cache[self.class] = error
           raise

test/spec_request.rb

@@ -1554,12 +1554,19 @@ def initialize(*)
     rack_input.write(input)
     rack_input.rewind
 
-    req = make_request Rack::MockRequest.env_for("/",
-                      "rack.request.form_hash" => { 'foo' => 'bar' },
-                      "rack.request.form_input" => rack_input,
-                      :input => rack_input)
+    form_hash_cache = {}
+
+    req = make_request Rack::MockRequest.env_for(
+      "/",
+      "rack.request.form_hash" => form_hash_cache,
+      "rack.request.form_input" => rack_input,
+      :input => rack_input
+    )
+
+    form_hash = {'foo' => 'bar'}.freeze
+    form_hash_cache[req.class] = form_hash
 
-    req.POST.must_equal req.env['rack.request.form_hash']
+    req.POST.must_equal form_hash
   end
 
   it "conform to the Rack spec" do