Don't pin named structs defined in Ruby

[Bug #20311]

`rb_define_class_under` assumes it's called from C and that the
reference might be held in a C global variable, so it adds the
class to the VM root.

In the case of `Struct.new('Name')` it's wasteful and make
the struct immortal.

1 files changed, 1 insertions, 0 deletions

diff --git a/internal/class.h b/internal/class.h
index 74ad956e3e..594f1daea7 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -175,6 +175,7 @@ void rb_class_foreach_subclass(VALUE klass, void (*f)(VALUE, VALUE), VALUE);
 void rb_class_detach_subclasses(VALUE);
 void rb_class_detach_module_subclasses(VALUE);
 void rb_class_remove_from_module_subclasses(VALUE);
+VALUE rb_define_class_id_under_no_pin(VALUE outer, ID id, VALUE super);
 VALUE rb_obj_methods(int argc, const VALUE *argv, VALUE obj);
 VALUE rb_obj_protected_methods(int argc, const VALUE *argv, VALUE obj);
 VALUE rb_obj_private_methods(int argc, const VALUE *argv, VALUE obj);