Revert "Auto-load template handlers based on unmatched extensions [#1540 state:resolved]"

This reverts commit e8c19154.

Reasons :
- ActionPack tests run very slow
- Gem.searcher hanging for long time when extension is nil

actionpack/lib/action_view/template.rb

@@ -98,6 +98,10 @@ def load!
     end
 
     private
+      def valid_extension?(extension)
+        Template.template_handler_extensions.include?(extension)
+      end
+
       def find_full_path(path, load_paths)
         load_paths = Array(load_paths) + [nil]
         load_paths.each do |load_path|
@@ -111,11 +115,11 @@ def find_full_path(path, load_paths)
       #   [base_path, name, format, extension]
       def split(file)
         if m = file.match(/^(.*\/)?([^\.]+)\.?(\w+)?\.?(\w+)?\.?(\w+)?$/)
-          if Template.valid_extension?(m[5]) # Multipart formats
+          if valid_extension?(m[5]) # Multipart formats
             [m[1], m[2], "#{m[3]}.#{m[4]}", m[5]]
-          elsif Template.valid_extension?(m[4]) # Single format
+          elsif valid_extension?(m[4]) # Single format
             [m[1], m[2], m[3], m[4]]
-          elsif Template.valid_extension?(m[3]) # No format
+          elsif valid_extension?(m[3]) # No format
             [m[1], m[2], nil, m[3]]
           else # No extension
             [m[1], m[2], m[3], nil]

actionpack/lib/action_view/template_handlers.rb

@@ -28,10 +28,6 @@ def register_template_handler(extension, klass)
       @@template_handlers[extension.to_sym] = klass
     end
 
-    def valid_extension?(extension)
-      template_handler_extensions.include?(extension) || init_path_for_extension(extension)
-    end
-
     def template_handler_extensions
       @@template_handlers.keys.map(&:to_s).sort
     end
@@ -42,26 +38,7 @@ def register_default_template_handler(extension, klass)
     end
 
     def handler_class_for_extension(extension)
-      (extension && @@template_handlers[extension.to_sym] || autoload_handler_class(extension)) ||
-        @@default_template_handlers
-    end
-
-    private
-      def autoload_handler_class(extension)
-        return if Gem.loaded_specs[extension]
-        return unless init_path = init_path_for_extension(extension)
-        Gem.activate(extension)
-        load(init_path)
-        handler_class_for_extension(extension)
-      end
-
-      # Returns the path to the rails/init.rb file for the given extension,
-      # or nil if no gem provides it.
-      def init_path_for_extension(extension)
-        return unless spec = Gem.searcher.find(extension.to_s)
-        returning File.join(spec.full_gem_path, 'rails', 'init.rb') do |path|
-          return unless File.file?(path)
-        end
+      (extension && @@template_handlers[extension.to_sym]) || @@default_template_handlers
     end
   end
 end