Add initial support for partials

lib/json_builder/compiler.rb

@@ -1,5 +1,6 @@
 require 'json'
 require 'json_builder/member'
+require 'json_builder/partial'
 
 module JSONBuilder
   class Compiler
@@ -71,6 +72,17 @@ def array(items, &block)
       @_array = Elements.new(@_scope, items, &block)
     end
 
+    # Public: Executes an extracted bit of JSONBuilder view code on the parent
+    # JSONBuilder::Compiler object.
+    #
+    # args - could be string or options
+    #
+    # Returns nothing.
+    def partial(*args)
+      partial = Partial.new(*args)
+      instance_eval partial.source
+    end
+
     # Public: Called anytime the compiler is passed JSON keys,
     # first checks to see if the parent object contains the method like
     # a Rails helper.

lib/json_builder/partial.rb

@@ -0,0 +1,48 @@
+require 'active_support/notifications'
+
+module JSONBuilder
+  class Partial
+    class MissingTemplate < StandardError; end;
+
+    attr_accessor :object
+    attr_accessor :options
+    attr_accessor :path
+
+    def initialize(*args)
+      @options = args.extract_options!
+      @object = args.first
+
+      setup @object, @options
+    end
+
+    def setup(object, options)
+      if (Object.const_defined?('ActiveRecord') && ActiveRecord::Base === object.superclass) || object.respond_to?(:to_partial_path)
+        begin
+          @path = object.to_partial_path
+        rescue
+          raise ArgumentError.new("'#{object.inspect}' is not an ActiveModel-compatible object. It must implement :to_partial_path.")
+        end
+      end
+
+      if String === object
+        @path = object
+      end
+    end
+
+    def source
+      instrument :template do
+        begin
+          File.read @path
+        rescue Errno::ENOENT
+          raise MissingTemplate
+        end
+      end
+    end
+
+    private
+
+    def instrument(name, options = {})
+      ActiveSupport::Notifications.instrument("render_#{name}.action_view", options) { yield }
+    end
+  end
+end

test/compiler_test.rb

@@ -100,4 +100,14 @@ def test_newline_characters
       newline "hello\nworld"
     end
   end
+
+  def test_partial_compilation
+    assert_builder_json('{"results": 500, "embedded": "partial", "metadata": {"expires": "soon"}}') do
+      results 500
+      partial File.expand_path('../fixtures/_partial.json_builder', __FILE__)
+      metadata do
+        expires "soon"
+      end
+    end
+  end
 end

test/fixtures/_partial.json_builder

@@ -0,0 +1 @@
+embedded "partial"

test/partial_test.rb

@@ -0,0 +1,29 @@
+# encoding: UTF-8
+
+require 'test_helper'
+
+class User
+  def to_partial_path
+    'users'
+  end
+end
+
+class TestPartial < Test::Unit::TestCase
+  def partial(*args)
+    JSONBuilder::Partial.new(*args)
+  end
+
+  def test_partial_file_path_from_model
+    assert_equal 'users', partial(User.new).path
+  end
+
+  def test_passed_in_partial_path
+    assert_equal 'custom/path', partial('custom/path').path
+  end
+
+  def test_missing_partial_file
+    assert_raise(JSONBuilder::Partial::MissingTemplate) {
+      partial('test/me').source
+    }
+  end
+end