Prawn::View#method_missing drops keyword arguments on Ruby 3.x

[Burgestrand]

Hi! This is my first message about this issue — I figured starting with a PR would make the issue more clear. I'm betting on CI running this code on older versions of Ruby to make sure this doesn't break anything by accident.

Ruby 3.x changes behavior of keyword arguments when used with single splat *arguments. Prawn::View#method_missing delegates missing methods to the document, but keyword arguments are dropped in the delegation in Ruby 3.

There aren't that many Prawn::Document methods that takes keyword arguments (I pretty much only found the gradient methods). We ran into this in our own code because we've added a few helper methods to Prawn::Document that does take keyword arguments, and we noticed in our upgrade to Ruby 3.x we couldn't use those methods.

In our own code we've temporarily fixed this with a monkey patch:

module Prawn::View
  ruby2_keywords :method_missing
end

Here's an example of behavior changed in Ruby 3.x vs 2.x:

def original(*args, **kwargs)
  p({ args: args, kwargs: kwargs })
end

def forward(*args)
  original(*args)
end

forward(1, 2, x: "x", y: "y")
# Ruby 2.7: {:args=>[1, 2], :kwargs=>{:x=>"x", :y=>"y"}}
# Ruby 3.x: {:args=>[1, 2, {:x=>"x", :y=>"y"}], :kwargs=>{}}

[pointlessone]

@Burgestrand Thank you for your contribution. This was merged outside of GitHub.