Stop infinite recursion in `Class#to_s`; fix
MODIFY
src/variable.c
src/variable.c
@@ -948,6 +948,7 @@ find_class_sym(mrb_state *mrb, struct RClass *outer, struct RClass *c)
struct csym_arg arg;
if (!outer) return 0;
+ if (outer == c) return 0;
arg.c = c;
arg.sym = 0;
iv_foreach(mrb, outer->iv, csym_i, &arg);

Stop infinite recursion in `Class#to_s`; fix #3861