From: merch-redmine@...
Date: 2021-06-29T14:52:38+00:00
Subject: [ruby-core:104441] [Ruby master Bug#18011] `Method#parameters` is incorrect for forwarded arguments

Issue #18011 has been updated by jeremyevans0 (Jeremy Evans).


Eregon (Benoit Daloze) wrote in #note-3:
> IMHO in Ruby 3+ it should return `[[:rest, :*], [:keyrest, :**], [:block, :&]]`.
> 
> The fact that it uses `ruby2_keywords` internally is an implementation detail that I don't think needs to leak into Method#parameters.

I think methods that use `ruby2_keywords`, either explicitly or implicitly through argument forwarding, should handle `parameters` consistently.  However, I'm fine with all `ruby2_keywords` methods adding `[:keyrest, :**]` as opposed to adding `[:ruby2_keywords]`.  The `:keyrest` approach may be more backwards compatible.

Note that from a caller's perspective, `[[:rest, :*]]` and `[[:rest, :*], [:keyrest, :**]]` have identical behavior. Both accept an arbitrary number of positional argument and arbitrary keywords.

----------------------------------------
Bug #18011: `Method#parameters` is incorrect for forwarded arguments
https://bugs.ruby-lang.org/issues/18011#change-92693

* Author: josh.cheek (Josh Cheek)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [arm64-darwin20]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
When asking a method about its parameters, forwarded arguments say they are a rest and a block (`wrapper1` in the example below).
However, when we use that signature, it raises an ArgumentError (`wrapper2` in the example below).
When I add a keyrest to the signature, it works as expected (`wrapper3` in the example below).
So I think forwarded arguments should include a keyrest in the output of `Method#parameters`

```ruby
def wrapped(ord, kw:) = [ord, {kw: kw}]

methods = [
 def wrapper1(...)         = wrapped(...),
 def wrapper2(*r, &b)      = wrapped(*r, &b),
 def wrapper3(*r, **k, &b) = wrapped(*r, **k, &b),
]

methods.each do |name|
  puts File.read(__FILE__)[/#{name}\(.*?\)/]
  puts "  params: #{method(name).parameters.inspect}"
  puts "  result: #{(method(name).call 123, kw: 456 rescue $!).inspect}"
  puts
end
```

Output:

```
wrapper1(...)
  params: [[:rest, :*], [:block, :&]]
  result: [123, {:kw=>456}]

wrapper2(*r, &b)
  params: [[:rest, :r], [:block, :b]]
  result: #<ArgumentError: wrong number of arguments (given 2, expected 1; required keyword: kw)>

wrapper3(*r, **k, &b)
  params: [[:rest, :r], [:keyrest, :k], [:block, :b]]
  result: [123, {:kw=>456}]
```



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