compile.c: avoid newarraykwsplat for arguments

`foo(*rest, post, **empty_kw)` is compiled like
`foo(*rest + [post, **empty_kw])`, and `**empty_kw` is removed by
"newarraykwsplat" instruction.
However, the method call still has a flag of KW_SPLAT, so "post" is
considered as a keyword hash, which caused a segfault.
Note that the flag cannot be removed if "empty_kw" is not always empty.

This change fixes the issue by compiling arguments with "newarray"
instead of "newarraykwsplat".

[Bug #16442]

compile.c

@@ -5017,7 +5017,14 @@ setup_args_core(rb_iseq_t *iseq, LINK_ANCHOR *const args, const NODE *argn,
           case NODE_ARGSPUSH: {
             int next_is_list = (nd_type(argn->nd_head) == NODE_LIST);
             VALUE argc = setup_args_core(iseq, args, argn->nd_head, 1, NULL, NULL);
-            NO_CHECK(COMPILE(args, "args (cat: splat)", argn->nd_body));
+            if (nd_type(argn->nd_body) == NODE_LIST) {
+                /* This branch is needed to avoid "newarraykwsplat" [Bug #16442] */
+                int rest_len = compile_args(iseq, args, argn->nd_body, NULL, NULL);
+                ADD_INSN1(args, nd_line(argn), newarray, INT2FIX(rest_len));
+            }
+            else {
+                NO_CHECK(COMPILE(args, "args (cat: splat)", argn->nd_body));
+            }
             if (flag) {
                 *flag |= VM_CALL_ARGS_SPLAT;
                 /* This is a dirty hack.  It traverses the AST twice.

test/ruby/test_keyword.rb

@@ -4654,6 +4654,12 @@ class TestKeywordArguments < Test::Unit::TestCase
   def test_splat_empty_hash_with_block_passing
     assert_valid_syntax("bug15087(**{}, &nil)")
   end
+
+  def test_do_not_use_newarraykwsplat
+    assert_equal([42, "foo", 424242], f2(*[], 42, **{}))
+    a = [1, 2, 3]
+    assert_equal([[1,2,3,4,5,6], "foo", 424242, {:k=>:k}], f7(*a, 4,5,6, k: :k))
+  end
 end
 
 class TestKeywordArgumentsSymProcRefinements < Test::Unit::TestCase