1 files changed, 43 insertions, 0 deletions
diff --git a/actionpack/lib/abstract_controller/collector.rb b/actionpack/lib/abstract_controller/collector.rb
new file mode 100644
index 0000000000..d4a078ab32
--- /dev/null
+++ b/actionpack/lib/abstract_controller/collector.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require "action_dispatch/http/mime_type"
+
+module AbstractController
+  module Collector
+    def self.generate_method_for_mime(mime)
+      sym = mime.is_a?(Symbol) ? mime : mime.to_sym
+      class_eval <<-RUBY, __FILE__, __LINE__ + 1
+        def #{sym}(*args, &block)
+          custom(Mime[:#{sym}], *args, &block)
+        end
+      RUBY
+    end
+
+    Mime::SET.each do |mime|
+      generate_method_for_mime(mime)
+    end
+
+    Mime::Type.register_callback do |mime|
+      generate_method_for_mime(mime) unless instance_methods.include?(mime.to_sym)
+    end
+
+  private
+
+    def method_missing(symbol, &block)
+      unless mime_constant = Mime[symbol]
+        raise NoMethodError, "To respond to a custom format, register it as a MIME type first: " \
+          "https://guides.rubyonrails.org/action_controller_overview.html#restful-downloads. " \
+          "If you meant to respond to a variant like :tablet or :phone, not a custom format, " \
+          "be sure to nest your variant response within a format response: " \
+          "format.html { |html| html.tablet { ... } }"
+      end
+
+      if Mime::SET.include?(mime_constant)
+        AbstractController::Collector.generate_method_for_mime(mime_constant)
+        send(symbol, &block)
+      else
+        super
+      end
+    end
+  end
+end