Revert 88d08f2ec9

This caused a performance regression since we were decided to do the nil
check in run time not in the load time.

See https://github.com/rails/rails/pull/15187#issuecomment-71760058

activesupport/lib/active_support/core_ext/module/delegation.rb

@@ -185,19 +185,31 @@ class Module
       # On the other hand it could be that the target has side-effects,
       # whereas conceptually, from the user point of view, the delegator should
       # be doing one call.
-
-      exception = %(raise DelegationError, "#{self}##{method_prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}")
-
-      method_def = [
-        "def #{method_prefix}#{method}(#{definition})",
-        "  _ = #{to}",
-        "  if !_.nil? || nil.respond_to?(:#{method})",
-        "    _.#{method}(#{definition})",
-        "  else",
-        "    #{exception unless allow_nil}",
-        "  end",
+      if allow_nil
+        method_def = [
+          "def #{method_prefix}#{method}(#{definition})",
+          "_ = #{to}",
+          "if !_.nil? || nil.respond_to?(:#{method})",
+          "  _.#{method}(#{definition})",
+          "end",
         "end"
-      ].join ';'
+        ].join ';'
+      else
+        exception = %(raise DelegationError, "#{self}##{method_prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}")
+
+        method_def = [
+          "def #{method_prefix}#{method}(#{definition})",
+          " _ = #{to}",
+          "  _.#{method}(#{definition})",
+          "rescue NoMethodError => e",
+          "  if _.nil? && e.name == :#{method}",
+          "    #{exception}",
+          "  else",
+          "    raise",
+          "  end",
+          "end"
+        ].join ';'
+      end
 
       module_eval(method_def, file, line)
     end

activesupport/test/core_ext/module_test.rb

@@ -78,7 +78,7 @@ Product = Struct.new(:name) do
 
   def type
     @type ||= begin
-      :thing_without_same_method_name_as_delegated.name
+      nil.type_name
     end
   end
 end