Fix deep_merge_hashes! handling of drops and hashes

lib/jekyll/drops/drop.rb

@@ -127,6 +127,7 @@ module Jekyll
           result[key] = self[key]
         end
       end
+      alias_method :to_hash, :to_h
 
       # Inspect the drop's keys and values through a JSON representation
       # of its keys and values.
@@ -145,6 +146,31 @@ module Jekyll
       def each_key(&block)
         keys.each(&block)
       end
+
+      def merge(other, &block)
+        self.dup.tap do |me|
+          if block.nil?
+            me.merge!(other)
+          else
+            me.merge!(other, block)
+          end
+        end
+      end
+
+      def merge!(other)
+        other.each_key do |key|
+          if block_given?
+            self[key] = yield key, self[key], other[key]
+          else
+            if Utils.mergable?(self[key]) && Utils.mergable?(other[key])
+              self[key] = Utils.deep_merge_hashes(self[key], other[key])
+              next
+            end
+
+            self[key] = other[key] unless other[key].nil?
+          end
+        end
+      end
     end
   end
 end

lib/jekyll/utils.rb

@@ -31,14 +31,12 @@ module Jekyll
     #
     # Thanks to whoever made it.
     def deep_merge_hashes!(target, overwrite)
-      overwrite.each_key do |key|
-        if (overwrite[key].is_a?(Hash) || overwrite[key].is_a?(Drops::Drop)) &&
-            (target[key].is_a?(Hash) || target[key].is_a?(Drops::Drop))
-          target[key] = Utils.deep_merge_hashes(target[key], overwrite[key])
-          next
+      target.merge!(overwrite) do |key, old_val, new_val|
+        if new_val.nil?
+          old_val
+        else
+          mergable?(old_val) && mergable?(new_val) ? deep_merge_hashes(old_val, new_val) : new_val
         end
-
-        target[key] = overwrite[key]
       end
 
       if target.respond_to?(:default_proc) && overwrite.respond_to?(:default_proc) && target.default_proc.nil?
@@ -48,6 +46,10 @@ module Jekyll
       target
     end
 
+    def mergable?(value)
+      value.is_a?(Hash) || value.is_a?(Drops::Drop)
+    end
+
     # Read array from the supplied hash favouring the singular key
     # and then the plural key, and handling any nil entries.
     #

test/test_utils.rb

@@ -13,7 +13,7 @@ class TestUtils < JekyllUnitTest
       merged = Utils.deep_merge_hashes(data, @site.site_payload)
       assert merged.is_a? Hash
       assert merged["site"].is_a? Drops::SiteDrop
-      assert_equal data["page"], {}
+      assert_equal data["page"], merged["page"]
     end
 
     should "merge a hash into a drop" do
@@ -22,7 +22,7 @@ class TestUtils < JekyllUnitTest
       merged = Utils.deep_merge_hashes(@site.site_payload, data)
       assert merged.is_a? Drops::UnifiedPayloadDrop
       assert merged["site"].is_a? Drops::SiteDrop
-      assert_equal data["page"], {}
+      assert_equal data["page"], merged["page"]
     end
   end