deprecate accessing mime types via constants

We don't want to manage a list of constants on `Mime::`.  Managing
constants is strange because it will break method caches, not to mention
looking up by a constant could cause troubles.  For example suppose
there is a top level constant `HTML`, but nobody registers the HTML mime
type and someone accesses `Mime::HTML`.  Instead of getting an error
about how the mime type doesn't exist, instead you'll get the top level
constant.

So, instead of directly accessing the constants, change this:

  Mime::HTML

To this:

  Mime::Type[:HTML]

3 files changed, 55 insertions, 7 deletions

diff --git a/actionpack/lib/action_dispatch/http/mime_type.rb b/actionpack/lib/action_dispatch/http/mime_type.rb
index ba6cf809ca..001bac977d 100644
--- a/actionpack/lib/action_dispatch/http/mime_type.rb
+++ b/actionpack/lib/action_dispatch/http/mime_type.rb
@@ -2,6 +2,7 @@ require 'set'
 require 'singleton'
 require 'active_support/core_ext/module/attribute_accessors'
 require 'active_support/core_ext/string/starts_ends_with'
+require 'active_support/deprecation'
 
 module Mime
   class Mimes < Array
@@ -35,6 +36,40 @@ module Mime
       return type if type.is_a?(Type)
       EXTENSION_LOOKUP.fetch(type.to_s) { |k| yield k }
     end
+
+    def const_missing(sym)
+      if Mime::Type.registered?(sym)
+        ActiveSupport::Deprecation.warn <<-eow
+Accessing mime types via constants is deprecated.  Please change:
+
+  `Mime::#{sym}`
+
+to:
+
+  `Mime::Type[:#{sym}]`
+        eow
+        Mime::Type[sym]
+      else
+        super
+      end
+    end
+
+    def const_defined?(sym, inherit = true)
+      if Mime::Type.registered?(sym)
+        ActiveSupport::Deprecation.warn <<-eow
+Accessing mime types via constants is deprecated.  Please change:
+
+  `Mime::#{sym}`
+
+to:
+
+  `Mime::Type[:#{sym}]`
+        eow
+        true
+      else
+        super
+      end
+    end
   end
 
   # Encapsulates the notion of a mime type. Can be used at render time, for example, with:
@@ -66,7 +101,7 @@ module Mime
       def initialize(index, name, q = nil)
         @index = index
         @name = name
-        q ||= 0.0 if @name == Mime::ALL.to_s # default wildcard match to end of list
+        q ||= 0.0 if @name == Mime::Type[:ALL].to_s # default wildcard match to end of list
         @q = ((q || 1.0).to_f * 100).to_i
       end
 
@@ -120,7 +155,7 @@ module Mime
         end
 
         def app_xml_idx
-          @app_xml_idx ||= index(Mime::XML.to_s)
+          @app_xml_idx ||= index(Mime::Type[:XML].to_s)
         end
 
         def text_xml
@@ -137,6 +172,8 @@ module Mime
         end
     end
 
+    TYPES = {}
+
     class << self
       TRAILING_STAR_REGEXP = /(text|application)\/\*/
       PARAMETER_SEPARATOR_REGEXP = /;\s*\w+="?\w+"?/
@@ -145,6 +182,18 @@ module Mime
         @register_callbacks << block
       end
 
+      def registered?(symbol)
+        TYPES.key? symbol
+      end
+
+      def [](symbol)
+        TYPES[symbol]
+      end
+
+      def add_type(symbol, type)
+        TYPES[symbol] = type
+      end
+
       def lookup(string)
         LOOKUP[string]
       end
@@ -161,7 +210,7 @@ module Mime
 
       def register(string, symbol, mime_type_synonyms = [], extension_synonyms = [], skip_lookup = false)
         new_mime = Type.new(string, symbol, mime_type_synonyms)
-        Mime.const_set(symbol.upcase, new_mime)
+        add_type symbol.upcase, new_mime
 
         SET << new_mime
 
@@ -216,8 +265,7 @@ module Mime
       #   Mime::Type.unregister(:mobile)
       def unregister(symbol)
         symbol = symbol.upcase
-        mime = Mime.const_get(symbol)
-        Mime.instance_eval { remove_const(symbol) }
+        mime = TYPES.delete symbol
 
         SET.delete_if { |v| v.eql?(mime) }
         LOOKUP.delete_if { |_,v| v.eql?(mime) }
diff --git a/actionpack/lib/action_dispatch/http/mime_types.rb b/actionpack/lib/action_dispatch/http/mime_types.rb
index 01a10c693b..d349cf2807 100644
--- a/actionpack/lib/action_dispatch/http/mime_types.rb
+++ b/actionpack/lib/action_dispatch/http/mime_types.rb
@@ -33,4 +33,4 @@ Mime::Type.register "application/pdf", :pdf, [], %w(pdf)
 Mime::Type.register "application/zip", :zip, [], %w(zip)
 
 # Create Mime::ALL but do not add it to the SET.
-Mime::ALL = Mime::Type.new("*/*", :all, [])
+Mime::Type.add_type :ALL, Mime::Type.new("*/*", :all, [])
diff --git a/actionpack/lib/action_dispatch/http/parameters.rb b/actionpack/lib/action_dispatch/http/parameters.rb
index 27fadb708e..e3c4392760 100644
--- a/actionpack/lib/action_dispatch/http/parameters.rb
+++ b/actionpack/lib/action_dispatch/http/parameters.rb
@@ -4,7 +4,7 @@ module ActionDispatch
       PARAMETERS_KEY = 'action_dispatch.request.path_parameters'
 
       DEFAULT_PARSERS = {
-        Mime::JSON => lambda { |raw_post|
+        Mime::Type[:JSON] => lambda { |raw_post|
           data = ActiveSupport::JSON.decode(raw_post)
           data.is_a?(Hash) ? data : {:_json => data}
         }