Introduce a context for rendering fixtures ERB.

Fixture files are passed through an ERB renderer before being read as
YAML. The rendering is currently done in the context of the main object,
so method definitons leak into other fixtures, and there is no clean
place to define fixture helpers.

After this commit, the ERB renderer will use a new subclass of
ActiveRecord::FixtureSet.context_class each time a fixture is rendered.

2 files changed, 34 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/fixture_set/file.rb b/activerecord/lib/active_record/fixture_set/file.rb
index fbd7a4d891..8132310c91 100644
--- a/activerecord/lib/active_record/fixture_set/file.rb
+++ b/activerecord/lib/active_record/fixture_set/file.rb
@@ -38,7 +38,8 @@ module ActiveRecord
         end
 
         def render(content)
-          ERB.new(content).result
+          context = ActiveRecord::FixtureSet::RenderContext.create_subclass.new
+          ERB.new(content).result(context.get_binding)
         end
 
         # Validate our unmarshalled data.
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index 8601414209..d241788a9b 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -119,6 +119,23 @@ module ActiveRecord
   # perhaps you should reexamine whether your application is properly testable. Hence, dynamic values
   # in fixtures are to be considered a code smell.
   #
+  # Helper methods defined in a fixture will not be available in other fixtures, to prevent against
+  # unwanted inter-test dependencies. Methods used by multiple fixtures should be defined in a module
+  # that is included in <tt>ActiveRecord::FixtureSet.context_class</tt>.
+  #
+  # - define a helper method in `test_helper.rb`
+  #     class FixtureFileHelpers
+  #       def file_sha(path)
+  #         Digest::SHA2.hexdigest(File.read(Rails.root.join('test/fixtures', path)))
+  #       end
+  #     end
+  #     ActiveRecord::FixtureSet.context_class.send :include, FixtureFileHelpers
+  #
+  # - use the helper method in a fixture
+  #     photo:
+  #       name: kitten.png
+  #       sha: <%= file_sha 'files/kitten.png' %>
+  #
   # = Transactional Fixtures
   #
   # Test cases can use begin+rollback to isolate their changes to the database instead of having to
@@ -529,6 +546,11 @@ module ActiveRecord
       Zlib.crc32(label.to_s) % MAX_ID
     end
 
+    # Superclass for the evaluation contexts used by ERB fixtures.
+    def self.context_class
+      @context_class ||= Class.new
+    end
+
     attr_reader :table_name, :name, :fixtures, :model_class, :config
 
     def initialize(connection, name, class_name, path, config = ActiveRecord::Base)
@@ -989,3 +1011,13 @@ module ActiveRecord
       end
   end
 end
+
+class ActiveRecord::FixtureSet::RenderContext # :nodoc:
+  def self.create_subclass
+    Class.new ActiveRecord::FixtureSet.context_class do
+      def get_binding
+        binding()
+      end
+    end
+  end
+end