Only raise DelegationError if it's is the source of the exception

This fixes situations where nested NoMethodError exceptions are masked
by delegations. This would cause confusion especially where there was a
problem in the Rails booting process because of a delegation in the
routes reloading code.

Fixes #10559

1 files changed, 27 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/module_test.rb b/activesupport/test/core_ext/module_test.rb
index ccf537e075..283b13ff8b 100644
--- a/activesupport/test/core_ext/module_test.rb
+++ b/activesupport/test/core_ext/module_test.rb
@@ -66,6 +66,23 @@ Tester = Struct.new(:client) do
   delegate :name, :to => :client, :prefix => false
 end
 
+Product = Struct.new(:name) do
+  delegate :name, :to => :manufacturer, :prefix => true
+  delegate :name, :to => :type, :prefix => true
+
+  def manufacturer
+    @manufacturer ||= begin
+      nil.unknown_method
+    end
+  end
+
+  def type
+    @type ||= begin
+      nil.type_name
+    end
+  end
+end
+
 class ParameterSet
   delegate :[], :[]=, :to => :@params
 
@@ -264,6 +281,16 @@ class ModuleTest < ActiveSupport::TestCase
     assert_equal [3], se.ints
   end
 
+  def test_delegation_doesnt_mask_nested_no_method_error_on_nil_receiver
+    product = Product.new('Widget')
+
+    # Nested NoMethodError is a different name from the delegation
+    assert_raise(NoMethodError) { product.manufacturer_name }
+
+    # Nested NoMethodError is the same name as the delegation
+    assert_raise(NoMethodError) { product.type_name }
+  end
+
   def test_parent
     assert_equal Yz::Zy, Yz::Zy::Cd.parent
     assert_equal Yz, Yz::Zy.parent