Use #ruby2_keywords for correct delegation on Ruby <= 2.6, 2.7 and 3

* See https://www.ruby-lang.org/en/news/2019/12/12/separation-of-positional-and-keyword-arguments-in-ruby-3-0/#a-compatible-delegation

Author: eregon

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 * Your contribution here.
 * [#2131](https://github.com/ruby-grape/grape/pull/2131): Fix Ruby 2.7 keyword deprecation warning in validators/coerce - [@K0H205](https://github.com/K0H205).
+* [#2132](https://github.com/ruby-grape/grape/pull/2132): Use #ruby2_keywords for correct delegation on Ruby <= 2.6, 2.7 and 3 - [@eregon](https://github.com/eregon).
 
 ### 1.5.1 (2020/11/15)
 

lib/grape/middleware/stack.rb

@@ -6,12 +6,11 @@ module Middleware
     # It allows to insert and insert after
     class Stack
       class Middleware
-        attr_reader :args, :opts, :block, :klass
+        attr_reader :args, :block, :klass
 
-        def initialize(klass, *args, **opts, &block)
+        def initialize(klass, *args, &block)
           @klass = klass
-          @args  = args
-          @opts  = opts
+          @args = args
           @block = block
         end
 
@@ -32,16 +31,8 @@ def inspect
           klass.to_s
         end
 
-        if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.7')
-          def use_in(builder)
-            block ? builder.use(klass, *args, **opts, &block) : builder.use(klass, *args, **opts)
-          end
-        else
-          def use_in(builder)
-            args  = self.args
-            args += [opts] unless opts.empty?
-            block ? builder.use(klass, *args, &block) : builder.use(klass, *args)
-          end
+        def use_in(builder)
+          builder.use(@klass, *@args, &@block)
         end
       end
 
@@ -70,23 +61,26 @@ def [](i)
         middlewares[i]
       end
 
-      def insert(index, *args, **kwargs, &block)
+      def insert(index, *args, &block)
         index = assert_index(index, :before)
-        middleware = self.class::Middleware.new(*args, **kwargs, &block)
+        middleware = self.class::Middleware.new(*args, &block)
         middlewares.insert(index, middleware)
       end
+      ruby2_keywords :insert if respond_to?(:ruby2_keywords, true)
 
       alias insert_before insert
 
       def insert_after(index, *args, &block)
         index = assert_index(index, :after)
         insert(index + 1, *args, &block)
       end
+      ruby2_keywords :insert_after if respond_to?(:ruby2_keywords, true)
 
-      def use(*args, **kwargs, &block)
-        middleware = self.class::Middleware.new(*args, **kwargs, &block)
+      def use(*args, &block)
+        middleware = self.class::Middleware.new(*args, &block)
         middlewares.push(middleware)
       end
+      ruby2_keywords :use if respond_to?(:ruby2_keywords, true)
 
       def merge_with(middleware_specs)
         middleware_specs.each do |operation, *args|

spec/grape/middleware/stack_spec.rb

@@ -35,8 +35,7 @@ def initialize(&block)
       expect { subject.use StackSpec::BarMiddleware, false, my_arg: 42 }
         .to change { subject.size }.by(1)
       expect(subject.last).to eq(StackSpec::BarMiddleware)
-      expect(subject.last.args).to eq([false])
-      expect(subject.last.opts).to eq(my_arg: 42)
+      expect(subject.last.args).to eq([false, { my_arg: 42 }])
     end
 
     it 'pushes a middleware class with block arguments onto the stack' do