Allow to pass method name to :with option of rescue_from

Closes #790

CHANGELOG.md

@@ -10,6 +10,7 @@
 * [#1243](https://github.com/ruby-grape/grape/pull/1243): Add `header` support for middleware - [@namusyaka](https://github.com/namusyaka).
 * [#1252](https://github.com/ruby-grape/grape/pull/1252): Allow default to be a subset or equal to allowed values without raising IncompatibleOptionValues - [@jeradphelps](https://github.com/jeradphelps).
 * [#1255](https://github.com/ruby-grape/grape/pull/1255): Allow param type definition in route_param - [@namusyaka](https://github.com/namusyaka)
+* [#1257](https://github.com/ruby-grape/grape/pull/1257): Allow to pass method name to :with option of rescue_from - [@namusyaka](https://github.com/namusyaka)
 * Your contribution here.
 
 #### Fixes

README.md

@@ -1771,6 +1771,22 @@ end
 
 The `rescue_from` block must return a `Rack::Response` object, call `error!` or re-raise an exception.
 
+The `with` keyword is available as `rescue_from` options, it can be passed method name or `Rack::Response` object.
+
+```ruby
+class Twitter::API < Grape::API
+  format :json
+  helpers do
+    def server_error!
+      error!({ error: 'Server error.' }, 500, { 'Content-Type' => 'text/error' })
+    end
+  end
+
+  rescue_from :all,          with: :server_error!
+  rescue_from ArgumentError, with: Rack::Response.new('rescued with a method', 400)
+end
+```
+
 #### Unrescuable Exceptions
 
 `Grape::Exceptions::InvalidVersionHeader`, which is raised when the version in the request header doesn't match the currently evaluated version for the endpoint, will _never_ be rescued from a `rescue_from` block (even a `rescue_from :all`) This is because Grape relies on Rack to catch that error and try the next versioned-route for cases where there exist identical Grape endpoints with different versions.

lib/grape/dsl/request_response.rb

@@ -105,7 +105,9 @@ def rescue_from(*args, &block)
           end
 
           options = args.extract_options!
-          handler ||= proc { options[:with] } if options.key?(:with)
+          if options.key?(:with) && !options[:with].instance_of?(Symbol)
+            handler ||= proc { options[:with] }
+          end
 
           if args.include?(:all)
             namespace_inheritable(:rescue_all, true)

lib/grape/middleware/error.rb

@@ -45,6 +45,10 @@ def find_handler(klass)
         handler = options[:rescue_handlers].find(-> { [] }) { |error, _| klass <= error }[1]
         handler ||= options[:base_only_rescue_handlers][klass]
         handler ||= options[:all_rescue_handler]
+        with_option = options[:rescue_options][:with]
+        if with_option.instance_of?(Symbol) && respond_to?(with_option)
+          handler ||= self.class.instance_method(with_option).bind(self)
+        end
         handler
       end
 

spec/grape/api_spec.rb

@@ -1518,6 +1518,22 @@ def rescue_arg_error
     end
   end
 
+  describe '.rescue_from klass, with: :method_name' do
+    it 'rescues an error with the specified method name' do
+      subject.helpers do
+        def rescue_arg_error
+          error!('500 ArgumentError', 500)
+        end
+      end
+      subject.rescue_from ArgumentError, with: :rescue_arg_error
+      subject.get('/rescue_method') { fail ArgumentError }
+
+      get '/rescue_method'
+      expect(last_response.status).to eq(500)
+      expect(last_response.body).to eq('500 ArgumentError')
+    end
+  end
+
   describe '.rescue_from klass, rescue_subclasses: boolean' do
     before do
       module ApiSpec