Prepend controller path to lookup_context prefixes

Rails rendering assumes that the first prefix encountered is 'special', specifically, it's the controller's prefix. This can be seen in `ActionView::AbstractRenderer::ObjectRendering#initialize`. This change injects the controller path at the start of the prefix list instead of the end to make sure this assumption is satisfied. Resolves#2729.

Author: sfnelson

lib/rspec/rails/example/view_example_group.rb

@@ -186,7 +186,7 @@ def _include_controller_helpers
 
 beforedo
 _include_controller_helpers
-view.lookup_context.prefixes << _controller_path
+view.lookup_context.prefixes.prepend(_controller_path)
 
 controller.controller_path=_controller_path
 

spec/rspec/rails/example/view_example_group_spec.rb

@@ -255,6 +255,26 @@ def _view; end # Stub method
 expect(failure_reporter.exceptions).toeq[]
 expect(run_count).toeq1
 end
+
+# Rails expects the first prefix to be the controller path.
+# @see ActionView::AbstractRenderer::ObjectRendering#initialize
+# Regression test for rspec/rspec-rails#2729
+it'injects controller path as first prefix'do
+prefixes=[]
+RSpec.describe"a view spec"do
+include ::RSpec::Rails::ViewExampleGroup
+
+def_controller_path
+"example/path"
+end
+
+specifydo
+prefixes=view.lookup_context.prefixes
+end
+end.run
+
+expect(prefixes).tostart_with("example/path")
+end
 end
 
 describe"#template"do