Remove incorrect setting of KW_SPLAT_MUT flag

Fixes [Bug #20701]

Co-authored-by: Pablo Herrero <[email protected]>

2 files changed, 12 insertions, 1 deletions

diff --git a/compile.c b/compile.c
index 366d32f9ec..cf75dce619 100644
--- a/compile.c
+++ b/compile.c
@@ -6249,7 +6249,6 @@ setup_args_core(rb_iseq_t *iseq, LINK_ANCHOR *const args, const NODE *argn,
         if (kwnode) {
             // kwsplat
             *flag_ptr |= VM_CALL_KW_SPLAT;
-            *flag_ptr |= VM_CALL_KW_SPLAT_MUT;
             compile_hash(iseq, args, kwnode, TRUE, FALSE);
             argc += 1;
         }
diff --git a/test/ruby/test_call.rb b/test/ruby/test_call.rb
index 570b5bb0a9..14847bf629 100644
--- a/test/ruby/test_call.rb
+++ b/test/ruby/test_call.rb
@@ -345,6 +345,18 @@ class TestCall < Test::Unit::TestCase
     assert_equal Hash, f(*[], **o).class
   end
 
+  def test_call_args_splat_with_pos_arg_kw_splat_is_not_mutable
+    o = Object.new
+    def o.foo(a, **h)= h[:splat_modified] = true
+
+    a = []
+    b = {splat_modified: false}
+
+    o.foo(*a, :x, **b)
+
+    assert_equal({splat_modified: false}, b)
+  end
+
   def test_kwsplat_block_order
     o = Object.new
     ary = []