RBS, Ruby’s new type signature language

note that syntax isn't actually new in ruby 2.7 or 3.0 at all. It's been around since ruby 2.0 in fact (Feb 2013). (keyword arguments had to be declared with default values until ruby 2.1, Dec 2013).

What ruby 2.7/3.0 do is rationalize some really weird counter-intuitive and ambiguous edge cases related to passing a Hash arg expecting it to be invoked as if it were keyword args. But it's a change in semantics, not syntax. The keyword argument syntax, keyword arguments with colons, in both method definitions and invocations, has been around for years, unchanged.