A positional Hash is not keyword arguments [Bug #18632]

spec/ruby/core/struct/new_spec.rb

@@ -60,11 +60,16 @@ describe "Struct.new" do
     -> { Struct.new(:animal, nil)                  }.should raise_error(TypeError)
     -> { Struct.new(:animal, true)                 }.should raise_error(TypeError)
     -> { Struct.new(:animal, ['chris', 'evan'])    }.should raise_error(TypeError)
+    ruby_version_is "3.2" do
+      -> { Struct.new(:animal, { name: 'chris' }) }.should raise_error(TypeError)
+    end
   end
 
+  ruby_version_is ""..."3.2" do
     it "raises a ArgumentError if passed a Hash with an unknown key" do
       -> { Struct.new(:animal, { name: 'chris' }) }.should raise_error(ArgumentError)
     end
+  end
 
   it "raises ArgumentError when there is a duplicate member" do
     -> { Struct.new(:foo, :foo) }.should raise_error(ArgumentError, "duplicate member: foo")

struct.c

@@ -576,8 +576,9 @@ rb_struct_s_def(int argc, VALUE *argv, VALUE klass)
     long i;
     VALUE st;
     st_table *tbl;
+    VALUE opt;
 
-    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
+    argc = rb_scan_args(argc, argv, "1*:", NULL, NULL, &opt);
     name = argv[0];
     if (SYMBOL_P(name)) {
 	name = Qnil;
@@ -587,20 +588,19 @@ rb_struct_s_def(int argc, VALUE *argv, VALUE klass)
 	++argv;
     }
 
-    if (RB_TYPE_P(argv[argc-1], T_HASH)) {
+    if (!NIL_P(opt)) {
 	static ID keyword_ids[1];
 
 	if (!keyword_ids[0]) {
 	    keyword_ids[0] = rb_intern("keyword_init");
 	}
-        rb_get_kwargs(argv[argc-1], keyword_ids, 0, 1, &keyword_init);
+        rb_get_kwargs(opt, keyword_ids, 0, 1, &keyword_init);
         if (keyword_init == Qundef) {
             keyword_init = Qnil;
         }
         else if (RTEST(keyword_init)) {
             keyword_init = Qtrue;
         }
-	--argc;
     }
 
     rest = rb_ident_hash_new();

test/ruby/test_struct.rb

@@ -100,8 +100,9 @@ module TestStruct
     assert_equal([:utime, :stime, :cutime, :cstime], Process.times.members)
   end
 
-  def test_struct_new_with_empty_hash
+  def test_struct_new_with_hash
-    assert_equal({:a=>1}, Struct.new(:a, {}).new({:a=>1}).a)
+    assert_raise_with_message(TypeError, /not a symbol/) {Struct.new(:a, {})}
+    assert_raise_with_message(TypeError, /not a symbol/) {Struct.new(:a, {name: "b"})}
   end
 
   def test_struct_new_with_keyword_init