First draft of ActiveSupport::Rescuable

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activesupport/lib/active_support/rescuable.rb

@@ -0,0 +1,74 @@
+module ActiveSupport
+  module Rescuable
+    def self.included(base) # :nodoc:
+      base.class_inheritable_array :rescue_handlers
+      base.rescue_handlers = []
+      base.extend(ClassMethods)
+    end
+
+    module ClassMethods
+      def enable_rescue_for(*methods)
+        methods.each do |method|
+          class_eval <<-EOS
+            def #{method}_with_rescue(*args, &block)
+              #{method}_without_rescue(*args, &block)
+            rescue Exception => exception
+              rescue_with_handler(exception)
+            end
+
+            alias_method_chain :#{method}, :rescue
+          EOS
+        end
+      end
+
+      def rescue_from(*klasses, &block)
+        options = klasses.extract_options!
+        unless options.has_key?(:with)
+          if block_given?
+            options[:with] = block
+          else
+            raise ArgumentError, "Need a handler. Supply an options hash that has a :with key as the last argument."
+          end
+        end
+
+        klasses.each do |klass|
+          key = if klass.is_a?(Class) && klass <= Exception
+            klass.name
+          elsif klass.is_a?(String)
+            klass
+          else
+            raise ArgumentError, "#{klass} is neither an Exception nor a String"
+          end
+
+          # put the new handler at the end because the list is read in reverse
+          rescue_handlers << [key, options[:with]]
+        end
+      end
+    end
+
+    def rescue_with_handler(exception)
+      if handler = handler_for_rescue(exception)
+        handler.arity != 0 ? handler.call(exception) : handler.call
+      else
+        raise exception
+      end
+    end
+
+    def handler_for_rescue(exception)
+      # use reverse so what is added last is found first
+      _, handler = *rescue_handlers.reverse.detect do |klass_name, handler|
+        # allow strings to support constants that are not defined yet
+        klass = self.class.const_get(klass_name) rescue nil
+        klass ||= klass_name.constantize rescue nil
+        exception.is_a?(klass) if klass
+      end
+
+      case handler
+      when Symbol
+        method(handler)
+      when Proc
+        handler.bind(self)
+      end
+    end
+  end
+end