Evaluate sequences within the context of the Evaluator when possible

This fixes weird issues where methods invoked within sequences
(like `sprintf`) fail because these methods are being evaluated within
the context of the DefinitionProxy. With this change, invoking `#next`
on a sequence happens from the evaluator so if the scope is provided (it
usually will be), it'll run in the proper context. This means a couple
of oddities are fixed:

1. Developers can now refer to methods on the object instance, just like
in dynamic attributes:

    class User
      def company
        # company lookup
      end
    end

    FactoryGirl.define do
      factory :user do
        sequence(:job_title) {|n| "{title} #{n} at #{company.name}" }
      end
    end

2. Invoke methods typically available because the method is available on
Object (e.g. Kernel methods):

    FactoryGirl.define do
      factory :user do
        sequence(:last_4_ssn) {|n| sprintf '%04d', n }
      end
    end

[#466]

gemfiles/3.0.gemfile.lock

@@ -1,5 +1,5 @@
 PATH
-  remote: /Users/mjankowski/Development/OpenSource/factory_girl
+  remote: /Users/joshuaclayton/dev/gems/factory_girl
   specs:
     factory_girl (4.1.0)
       activesupport (>= 3.0.0)

gemfiles/3.1.gemfile.lock

@@ -1,5 +1,5 @@
 PATH
-  remote: /Users/mjankowski/Development/OpenSource/factory_girl
+  remote: /Users/joshuaclayton/dev/gems/factory_girl
   specs:
     factory_girl (4.1.0)
       activesupport (>= 3.0.0)

gemfiles/3.2.gemfile.lock

@@ -1,5 +1,5 @@
 PATH
-  remote: /Users/mjankowski/Development/OpenSource/factory_girl
+  remote: /Users/joshuaclayton/dev/gems/factory_girl
   specs:
     factory_girl (4.1.0)
       activesupport (>= 3.0.0)

lib/factory_girl/definition_proxy.rb

@@ -108,7 +108,7 @@ module FactoryGirl
     # Except that no globally available sequence will be defined.
     def sequence(name, *args, &block)
       sequence = Sequence.new(name, *args, &block)
-      add_attribute(name) { sequence.next }
+      add_attribute(name) { increment_sequence(sequence) }
     end
 
     # Adds an attribute that builds an association. The associated instance will

lib/factory_girl/evaluator.rb

@@ -42,10 +42,18 @@ module FactoryGirl
       end
     end
 
+    def respond_to_missing?(method_name, include_private = false)
+      @instance.respond_to?(method_name) || SyntaxRunner.new.respond_to?(method_name)
+    end
+
     def __override_names__
       @overrides.keys
     end
 
+    def increment_sequence(sequence)
+      sequence.next(self)
+    end
+
     def self.attribute_list
       AttributeList.new.tap do |list|
         attribute_lists.each do |attribute_list|

lib/factory_girl/sequence.rb

@@ -19,10 +19,16 @@ module FactoryGirl
       end
     end
 
-    def next
+    def next(scope = nil)
-      @proc ? @proc.call(@value.peek) : @value.peek
+      if @proc && scope
+        scope.instance_exec(value, &@proc)
+      elsif @proc
+        @proc.call(value)
+      else
+        value
+      end
     ensure
-      @value.next
+      increment_value
     end
 
     def names
@@ -31,6 +37,14 @@ module FactoryGirl
 
     private
 
+    def value
+      @value.peek
+    end
+
+    def increment_value
+      @value.next
+    end
+
     class EnumeratorAdapter
       def initialize(value)
         @value = value

spec/acceptance/sequence_context_spec.rb

@@ -0,0 +1,52 @@
+require 'spec_helper'
+
+describe 'sequences are evaluated in the correct context' do
+  before do
+    define_class("User") do
+      attr_accessor :id
+
+      def awesome
+        'aw yeah'
+      end
+    end
+  end
+
+  it 'builds a sequence calling sprintf correctly' do
+    FactoryGirl.define do
+      factory :sequence_with_sprintf, class: User do
+        sequence(:id) {|n| sprintf("foo%d", n) }
+      end
+    end
+
+    FactoryGirl.build(:sequence_with_sprintf).id.should == 'foo1'
+  end
+
+  it 'invokes the correct method on the instance' do
+    FactoryGirl.define do
+      factory :sequence_with_public_method, class: User do
+        sequence(:id) {|n| public_method(:awesome).call }
+      end
+    end
+
+    FactoryGirl.build(:sequence_with_public_method).id.should == 'aw yeah'
+  end
+
+  it 'invokes a method with no arguments on the instance' do
+    FactoryGirl.define do
+      factory :sequence_with_frozen, class: User do
+        sequence(:id) {|n| frozen? }
+      end
+    end
+
+    FactoryGirl.build(:sequence_with_frozen).id.should be_false
+  end
+
+  it 'allows direct reference of a method in a sequence' do
+    FactoryGirl.define do
+      factory :sequence_referencing_attribute_directly, class: User do
+        sequence(:id) {|n| "#{awesome}#{n}" }
+      end
+    end
+    FactoryGirl.build(:sequence_referencing_attribute_directly).id.should == 'aw yeah1'
+  end
+end

spec/factory_girl/sequence_spec.rb

@@ -75,4 +75,21 @@ describe FactoryGirl::Sequence do
       expect { subject.next }.to raise_error(StopIteration)
     end
   end
+
+  describe "a custom sequence and scope" do
+    subject { FactoryGirl::Sequence.new(:name, 'A') {|n| "=#{n}#{foo}" } }
+    let(:scope) { stub('scope', foo: 'attribute') }
+
+    it 'increments within the correct scope' do
+      subject.next(scope).should == '=Aattribute'
+    end
+
+    describe 'when incrementing' do
+      before { subject.next(scope) }
+
+      it 'increments within the correct scope' do
+        subject.next(scope).should == '=Battribute'
+      end
+    end
+  end
 end