From cc8c4a60b7fbddc04e2e09946a3c70029db35d3d Mon Sep 17 00:00:00 2001
From: eileencodes <eileencodes@gmail.com>
Date: Tue, 2 Jul 2024 13:31:15 -0400
Subject: [PATCH] Calling into a C func shouldn't fast path when forwarding

When we forward calls to C functions if the callsite is a forwarding
site it might not always be a splat, so we can't use the fast path.

Fixes:

[ruby-core:118418]
---
 bootstraptest/test_method.rb | 15 +++++++++++++++
 vm_insnhelper.c              |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/bootstraptest/test_method.rb b/bootstraptest/test_method.rb
index 846d8e36a9..a5ea35dd4b 100644
--- a/bootstraptest/test_method.rb
+++ b/bootstraptest/test_method.rb
@@ -1344,3 +1344,18 @@ assert_equal 'ok', %q{
 
   C.new.foo
 }
+
+assert_equal 'ok', %q{
+  class C
+    def initialize(a)
+    end
+  end
+
+  def foo(...)
+    C.new(...)
+    :ok
+  end
+
+  foo(*["bar"])
+  foo("baz")
+}
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index be43e737fe..88feba74b9 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -3907,7 +3907,7 @@ vm_call_cfunc(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct rb
     const struct rb_callinfo *ci = calling->cd->ci;
     RB_DEBUG_COUNTER_INC(ccf_cfunc);
 
-    if (IS_ARGS_SPLAT(ci)) {
+    if (IS_ARGS_SPLAT(ci) && !(vm_ci_flag(ci) & VM_CALL_FORWARDING)) {
         if (!IS_ARGS_KW_SPLAT(ci) && vm_ci_argc(ci) == 1) {
             // f(*a)
             CC_SET_FASTPATH(calling->cc, vm_call_cfunc_only_splat, TRUE);