Add ability to render drops as JSON

Previously you could do, e.g. {{ site | jsonify }}, but with the introduction of Liquid Drops, this didn't work anymore.
This PR adds the ability to render drops as JSON. You can safely run drop.to_json and it should Do the Right Thing.

lib/jekyll/drops/document_drop.rb

@@ -5,10 +5,12 @@ module Jekyll
     class DocumentDrop < Drop
       extend Forwardable
 
+      NESTED_OBJECT_FIELD_BLACKLIST = %w{
+        content output excerpt next previous
+      }.freeze
+
       mutable false
 
-      def_delegator :@obj, :next_doc, :next
-      def_delegator :@obj, :previous_doc, :previous
       def_delegator :@obj, :relative_path, :path
       def_delegators :@obj, :id, :output, :content, :to_s, :relative_path, :url
 
@@ -27,6 +29,37 @@ module Jekyll
         cmp
       end
 
+      def previous
+        @obj.previous_doc.to_liquid
+      end
+
+      def next
+        @obj.next_doc.to_liquid
+      end
+
+      # Generate a Hash for use in generating JSON.
+      # This is useful if fields need to be cleared before the JSON can generate.
+      #
+      # Returns a Hash ready for JSON generation.
+      def hash_for_json(state = nil)
+        to_h.tap do |hash|
+          if state && state.depth >= 2
+            hash["previous"] = collapse_document(hash["previous"]) if hash["previous"]
+            hash["next"]     = collapse_document(hash["next"]) if hash["next"]
+          end
+        end
+      end
+
+      # Generate a Hash which breaks the recursive chain.
+      # Certain fields which are normally available are omitted.
+      #
+      # Returns a Hash with only non-recursive fields present.
+      def collapse_document(doc)
+        doc.keys.each_with_object({}) do |(key, _), result|
+          result[key] = doc[key] unless NESTED_OBJECT_FIELD_BLACKLIST.include?(key)
+        end
+      end
+
       private
       def_delegator :@obj, :data, :fallback_data
     end

lib/jekyll/drops/drop.rb

@@ -3,7 +3,9 @@
 module Jekyll
   module Drops
     class Drop < Liquid::Drop
-      NON_CONTENT_METHODS = [:[], :[]=, :inspect, :to_h, :fallback_data].freeze
+      include Enumerable
+
+      NON_CONTENT_METHODS = [:[], :[]=, :inspect, :to_h, :fallback_data, :collapse_document].freeze
 
       # Get or set whether the drop class is mutable.
       # Mutability determines whether or not pre-defined fields may be
@@ -138,6 +140,22 @@ module Jekyll
         JSON.pretty_generate to_h
       end
 
+      # Generate a Hash for use in generating JSON.
+      # This is useful if fields need to be cleared before the JSON can generate.
+      #
+      # Returns a Hash ready for JSON generation.
+      def hash_for_json(state = nil)
+        to_h
+      end
+
+      # Generate a JSON representation of the Drop.
+      #
+      # Returns a JSON representation of the Drop in a String.
+      def to_json(state = nil)
+        require 'json'
+        JSON.generate(hash_for_json(state), state)
+      end
+
       # Collects all the keys and passes each to the block in turn.
       #
       # block - a block which accepts one argument, the key

lib/jekyll/drops/jekyll_drop.rb

@@ -16,6 +16,18 @@ module Jekyll
       def environment
         Jekyll.env
       end
+
+      def to_h
+        @to_h ||= {
+          "version" => version,
+          "environment" => environment
+        }
+      end
+
+      def to_json(state = nil)
+        require 'json'
+        JSON.generate(to_h, state)
+      end
     end
   end
 end

lib/jekyll/site.rb

@@ -279,6 +279,7 @@ module Jekyll
     def site_payload
       Drops::UnifiedPayloadDrop.new self
     end
+    alias_method :to_liquid, :site_payload
 
     # Get the implementation class for the given Converter.
     # Returns the Converter instance implementing the given Converter.

test/test_document.rb

@@ -44,6 +44,46 @@ class TestDocument < JekyllUnitTest
       assert_equal "foo.bar", @document.data["whatever"]
     end
 
+    should "be jsonify-able" do
+      page_json = @document.to_liquid.to_json
+      parsed = JSON.parse(page_json)
+
+      assert_equal "Jekyll.configuration", parsed["title"]
+      assert_equal "foo.bar", parsed["whatever"]
+      assert_equal nil, parsed["previous"]
+
+      next_doc = parsed["next"]
+      assert_equal "_methods/escape-+ #%20[].md", next_doc["path"]
+      assert_equal "Jekyll.escape", next_doc["title"]
+
+      next_prev_doc = next_doc["previous"]
+      assert_equal "Jekyll.configuration", next_prev_doc["title"]
+      assert_equal "_methods/configuration.md", next_prev_doc["path"]
+      assert_equal "_methods/escape-+ #%20[].md", next_prev_doc["next"]["path"]
+      assert_nil next_prev_doc["previous"] # nothing before Jekyll.configuration
+      assert_nil next_prev_doc["next"]["next"]
+      assert_nil next_prev_doc["next"]["previous"]
+      assert_nil next_prev_doc["next"]["content"]
+      assert_nil next_prev_doc["next"]["excerpt"]
+      assert_nil next_prev_doc["next"]["output"]
+
+      next_next_doc = next_doc["next"]
+      assert_equal "Jekyll.sanitized_path", next_next_doc["title"]
+      assert_equal "_methods/sanitized_path.md", next_next_doc["path"]
+      assert_equal "_methods/escape-+ #%20[].md", next_next_doc["previous"]["path"]
+      assert_equal "_methods/site/generate.md", next_next_doc["next"]["path"]
+      assert_nil next_next_doc["next"]["next"]
+      assert_nil next_next_doc["next"]["previous"]
+      assert_nil next_next_doc["next"]["content"]
+      assert_nil next_next_doc["next"]["excerpt"]
+      assert_nil next_next_doc["next"]["output"]
+      assert_nil next_next_doc["previous"]["next"]
+      assert_nil next_next_doc["previous"]["previous"]
+      assert_nil next_next_doc["previous"]["content"]
+      assert_nil next_next_doc["previous"]["excerpt"]
+      assert_nil next_next_doc["previous"]["output"]
+    end
+
     context "with YAML ending in three dots" do
 
       setup do

test/test_filters.rb

@@ -198,6 +198,44 @@ class TestFilters < JekyllUnitTest
         assert_equal "[{\"name\":\"Jack\"},{\"name\":\"Smith\"}]", @filter.jsonify([{:name => 'Jack'}, {:name => 'Smith'}])
       end
 
+      should "convert drop to json" do
+        @filter.site.read
+        expected = {
+          "next" => "Categories _should_ work",
+          "path" => "_posts/2008-02-02-published.markdown",
+          "output" => nil,
+          "previous" => nil,
+          "content" => "This should be published.\n",
+          "id" => "/publish_test/2008/02/02/published",
+          "url" => "/publish_test/2008/02/02/published.html",
+          "relative_path" => "_posts/2008-02-02-published.markdown",
+          "collection" => "posts",
+          "excerpt" => "<p>This should be published.</p>\n",
+          "draft" => false,
+          "categories" => [
+            "publish_test"
+          ],
+          "layout" => "default",
+          "title" => "Publish",
+          "category" => "publish_test",
+          "date" => "2008-02-02 00:00:00 +0000",
+          "slug" => "published",
+          "ext" => ".markdown",
+          "tags" => []
+        }
+        actual = @filter.jsonify(@filter.site.docs_to_write.first.to_liquid)
+        assert_equal expected, JSON.parse(actual)
+      end
+
+      should "convert drop with drops to json" do
+        @filter.site.read
+        actual = @filter.jsonify(@filter.site.to_liquid)
+        assert_equal JSON.parse(actual)["jekyll"], {
+          "environment" => "development",
+          "version" => Jekyll::VERSION
+        }
+      end
+
       class M < Struct.new(:message)
         def to_liquid
           [message]