1 files changed, 24 insertions, 4 deletions
diff --git a/actionpack/lib/action_controller/metal/exceptions.rb b/actionpack/lib/action_controller/metal/exceptions.rb
index 175dd9eb9e..30034be018 100644
--- a/actionpack/lib/action_controller/metal/exceptions.rb
+++ b/actionpack/lib/action_controller/metal/exceptions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActionController
   class ActionControllerError < StandardError #:nodoc:
   end
@@ -20,7 +22,7 @@ module ActionController
     end
   end
 
-  class ActionController::UrlGenerationError < ActionControllerError #:nodoc:
+  class UrlGenerationError < ActionControllerError #:nodoc:
   end
 
   class MethodNotAllowed < ActionControllerError #:nodoc:
@@ -32,9 +34,6 @@ module ActionController
   class NotImplemented < MethodNotAllowed #:nodoc:
   end
 
-  class UnknownController < ActionControllerError #:nodoc:
-  end
-
   class MissingFile < ActionControllerError #:nodoc:
   end
 
@@ -51,4 +50,25 @@ module ActionController
 
   class UnknownFormat < ActionControllerError #:nodoc:
   end
+
+  # Raised when a nested respond_to is triggered and the content types of each
+  # are incompatible. For exampe:
+  #
+  #  respond_to do |outer_type|
+  #    outer_type.js do
+  #      respond_to do |inner_type|
+  #        inner_type.html { render body: "HTML" }
+  #      end
+  #    end
+  #  end
+  class RespondToMismatchError < ActionControllerError
+    DEFAULT_MESSAGE = "respond_to was called multiple times and matched with conflicting formats in this action. Please note that you may only call respond_to and match on a single format per action."
+
+    def initialize(message = nil)
+      super(message || DEFAULT_MESSAGE)
+    end
+  end
+
+  class MissingExactTemplate < UnknownFormat #:nodoc:
+  end
 end