Add support for anonymous rest and keyword rest argument forwarding

This allows for the following syntax:

```ruby
def foo(*)
  bar(*)
end
def baz(**)
  quux(**)
end
```

This is a natural addition after the introduction of anonymous
block forwarding.  Anonymous rest and keyword rest arguments were
already supported in method parameters, this just allows them to
be used as arguments to other methods.  The same advantages of
anonymous block forwarding apply to rest and keyword rest argument
forwarding.

This has some minor changes to #parameters output.  Now, instead
of `[:rest], [:keyrest]`, you get `[:rest, :*], [:keyrest, :**]`.
These were already used for `...` forwarding, so I think it makes
it more consistent to include them in other cases.  If we want to
use `[:rest], [:keyrest]` in both cases, that is also possible.

I don't think the previous behavior of `[:rest], [:keyrest]` in
the non-... case and `[:rest, :*], [:keyrest, :**]` in the ...
case makes sense, but if we did want that behavior, we'll have to
make more substantial changes, such as using a different ID in the
... forwarding case.

Implements [Feature #18351]

2 files changed, 22 insertions, 5 deletions

diff --git a/spec/ruby/core/method/parameters_spec.rb b/spec/ruby/core/method/parameters_spec.rb
index 3fdaf9ce6f..67b42afafa 100644
--- a/spec/ruby/core/method/parameters_spec.rb
+++ b/spec/ruby/core/method/parameters_spec.rb
@@ -222,9 +222,18 @@ describe "Method#parameters" do
     m.method(:handled_via_method_missing).parameters.should == [[:rest]]
   end
 
-  it "adds nameless rest arg for \"star\" argument" do
-    m = MethodSpecs::Methods.new
-    m.method(:one_unnamed_splat).parameters.should == [[:rest]]
+  ruby_version_is '3.1' do
+    it "adds * rest arg for \"star\" argument" do
+      m = MethodSpecs::Methods.new
+      m.method(:one_unnamed_splat).parameters.should == [[:rest, :*]]
+    end
+  end
+
+  ruby_version_is ''...'3.1' do
+    it "adds nameless rest arg for \"star\" argument" do
+      m = MethodSpecs::Methods.new
+      m.method(:one_unnamed_splat).parameters.should == [[:rest]]
+    end
   end
 
   it "returns the args and block for a splat and block argument" do
diff --git a/spec/ruby/core/proc/parameters_spec.rb b/spec/ruby/core/proc/parameters_spec.rb
index 5fb5cf418d..60620722f8 100644
--- a/spec/ruby/core/proc/parameters_spec.rb
+++ b/spec/ruby/core/proc/parameters_spec.rb
@@ -80,8 +80,16 @@ describe "Proc#parameters" do
     -> x {}.parameters.should == [[:req, :x]]
   end
 
-  it "adds nameless rest arg for \"star\" argument" do
-    -> x, * {}.parameters.should == [[:req, :x], [:rest]]
+  ruby_version_is '3.1' do
+    it "adds * rest arg for \"star\" argument" do
+      -> x, * {}.parameters.should == [[:req, :x], [:rest, :*]]
+    end
+  end
+
+  ruby_version_is ''...'3.1' do
+    it "adds nameless rest arg for \"star\" argument" do
+      -> x, * {}.parameters.should == [[:req, :x], [:rest]]
+    end
   end
 
   it "does not add locals as block options with a block and splat" do