YJIT: Support `**nil`

This adds YJIT support for VM_CALL_KW_SPLAT with nil, specifically for
when we already know from the context that it's done with a nil. This is
enough to support forwarding with `...` when there no keyword arguments
are present.

Amend the kw_rest support to propagate the type of the parameter to help
with this. Test interactions with splat, since the splat array sits
lower on the stack when a kw_splat argument is present.

1 files changed, 11 insertions, 0 deletions

diff --git a/test/ruby/test_yjit.rb b/test/ruby/test_yjit.rb
index f1b32226ec..b0a8337c11 100644
--- a/test/ruby/test_yjit.rb
+++ b/test/ruby/test_yjit.rb
@@ -1573,6 +1573,17 @@ class TestYJIT < Test::Unit::TestCase
     RUBY
   end
 
+  def test_kw_splat_nil
+    assert_compiles(<<~'RUBY', result: %i[ok ok], no_send_fallbacks: true)
+      def id(x) = x
+      def kw_fw(arg, **) = id(arg, **)
+      def fw(...) = id(...)
+      def use = [fw(:ok), kw_fw(:ok)]
+
+      use
+    RUBY
+  end
+
   private
 
   def code_gc_helpers