Fiddling with kwargs in Ruby 3 at https://try.ruby-lang.org/

input.rb

puts RUBY_VERSION

def foo(params={}, x: nil, **kwargs)
  puts({params: params, x: x, kwargs: kwargs})
end

foo(a: 1)
foo(a: 1, x: 2)
foo(x: 1)
foo({a: 1})
foo({a: 1}, x: 1)
foo(a: 1, x: 1, b: 2)
foo({a: 1}, x: 1, b: 2)

output.txt

3.1.0
{"params"=>{}, "x"=>nil, "kwargs"=>{"a"=>1}}
{"params"=>{}, "x"=>2, "kwargs"=>{"a"=>1}}
{"params"=>{}, "x"=>1, "kwargs"=>{}}
{"params"=>{}, "x"=>nil, "kwargs"=>{"a"=>1}}
{"params"=>{"a"=>1}, "x"=>1, "kwargs"=>{}}
{"params"=>{}, "x"=>1, "kwargs"=>{"a"=>1, "b"=>2}}
{"params"=>{"a"=>1}, "x"=>1, "kwargs"=>{"b"=>2}}