[Feature #19979] Method definition with &nil

Allow methods to declare that they don't accept a block via `&nil`.

Author: nobu

language/block_spec.rb

@@ -1110,6 +1110,17 @@ def o.it
       end
     end
   end
+
+  ruby_version_is "3.4" do
+    it "works alongside disallowed block argument" do
+      no_block = eval <<-EOF
+        proc {|arg1, &nil| arg1}
+      EOF
+
+      no_block.call(:a).should == :a
+      -> { no_block.call(:a) {} }.should raise_error(ArgumentError, 'no block accepted')
+    end
+  end
 end
 
 # Duplicates specs in language/it_parameter_spec.rb

language/method_spec.rb

@@ -1127,6 +1127,18 @@ def m(a, b = nil, c = nil, d, e: nil, **f)
       result = m(1, {foo: :bar})
       result.should == [1, nil, nil, {foo: :bar}, nil, {}]
     end
+
+    ruby_version_is "3.4" do
+      evaluate <<-ruby do
+        def m(a, &nil); a end;
+        ruby
+
+        m(1).should == 1
+
+        -> { m(1) {} }.should raise_error(ArgumentError, 'no block accepted')
+        -> { m(1, &proc {}) }.should raise_error(ArgumentError, 'no block accepted')
+      end
+    end
   end
 
   context 'when passing an empty keyword splat to a method that does not accept keywords' do