Freeze singleton class, not its origin

Previously, when we froze an object, we froze
`RCLASS_ORIGIN(object.singleton_class)`, which didn't freeze
`object.singleton_class` when it has some prepended modules.

Origin iclass are internal objects and users can't interact with
them through Kernel#freeze?, Kernel#freeze, or any mutation method
that checks the frozen status. So we shouldn't touch the origin
iclasses when the frozen status should be visible.

[Bug #19169]

1 files changed, 1 insertions, 1 deletions

diff --git a/class.c b/class.c
index 87ebabef32..55bc761ebe 100644
--- a/class.c
+++ b/class.c
@@ -2148,7 +2148,7 @@ rb_freeze_singleton_class(VALUE x)
     /* should not propagate to meta-meta-class, and so on */
     if (!(RBASIC(x)->flags & FL_SINGLETON)) {
         VALUE klass = RBASIC_CLASS(x);
-        if (klass && (klass = RCLASS_ORIGIN(klass)) != 0 &&
+        if (klass && // no class when hidden from ObjectSpace
             FL_TEST(klass, (FL_SINGLETON|FL_FREEZE)) == FL_SINGLETON) {
             OBJ_FREEZE_RAW(klass);
         }