Preserve anonymous parameters in generated RBIs

[Morriar]

Ruby reflects anonymous splat, keyword splat, and block parameters using pseudo-names:

def foo(*, **, &); end

method(:foo).parameters
# => [[:rest, :*], [:keyrest, :**], [:block, :&]]

Tapioca was treating those names as invalid parameter names and replacing them with fallback names like _arg0, _arg1, and _arg2. That caused two issues:

• Methods were generated with named parameters instead of preserving the original anonymous syntax.
• RBS-translated signatures could lose parameter types because Sorbet keeps the signature types under the original names: "*", "**", and "&".

For example, this could generate invalid RBI like:

sig { params(_arg0: , _arg1: , _arg2: ).void }
def foo(*_arg0, **_arg1, &_arg2); end

This change preserves anonymous parameter names for signature lookup, while rendering them as anonymous RBI parameters:

sig { params("*": ::Integer, "**": ::String, "&": T.proc.void).void }
def foo(*, **, &); end

It also bumps the minimum rbi dependency to 0.4.1, since older versions don’t support anonymous RestParam, KwRestParam, and BlockParam nodes represented with nil names.

[amomchilov]

Suggested change

	anonymous_parameter = anonymous_parameter_name?(type, name)
	name = fallback_arg_name unless anonymous_parameter || valid_parameter_name?(name)
	[type, name]
	[type, name, anonymous_parameter]
	is_anonymous_parameter = anonymous_parameter_name?(type, name)
	name = fallback_arg_name unless is_anonymous_parameter || valid_parameter_name?(name)
	[type, name, is_anonymous_parameter]

[amomchilov]

Suggested change

	sanitized_parameters.each do |type, name, anonymous_parameter|
	sanitized_parameters.each do |type, name, is_anonymous_parameter|

[amomchilov]

Do we need to thread the 3rd parameter through like this?

Could we instead modify the definition of name above, where anonymous_parameter is first set?

[amomchilov]

rc

[Morriar]

We need to pass something because the method param needs to be generated with a nil name but the signature param lookup needs the "*" name.

I change the tuple to use both names instead of passing the anonymous flag 👍