instance_eval should pass the receiver as a block parameter; close #3029

src/vm.c

@@ -510,11 +510,13 @@ eval_under(mrb_state *mrb, mrb_value self, mrb_value blk, struct RClass *c)
   }
   ci = mrb->c->ci;
   if (ci->acc == CI_ACC_DIRECT) {
-    return mrb_yield_with_class(mrb, blk, 0, 0, self, c);
+    return mrb_yield_with_class(mrb, blk, 1, &self, self, c);
   }
   ci->target_class = c;
   p = mrb_proc_ptr(blk);
   ci->proc = p;
+  ci->argc = 1;
+  mrb->c->stack[1] = self;
   if (MRB_PROC_CFUNC_P(p)) {
     return p->body.func(mrb, self);
   }