In a dump, the closure has the CLONED flag. You can also see the capture.
SV = IV(0x582c494d89d0) at 0x582c494d89e0
REFCNT = 1
FLAGS = (ROK)
RV = 0x582c494b36b0
SV = PVCV(0x582c495314a8) at 0x582c494b36b0
REFCNT = 2
FLAGS = (ANON,CLONED,CVGV_RC,DYNFILE)
COMP_STASH = 0x582c494b3530 "main"
START = 0x582c494f9298 ===> 1
ROOT = 0x582c494f9220
GVGV::GV = 0x582c494eed80 "main" :: "__ANON__"
FILE = "-"
DEPTH = 0
FLAGS = 0x14c0
OUTSIDE_SEQ = 218
PADLIST = 0x582c494ca480
PADNAME = 0x582c494f87a0(0x582c494d5cc0) PAD = 0x582c494d8878(0x58
+2c494df290)
1. 0x582c494eeb88<2> FAKE "$x" flags=0x0 index=2
OUTSIDE = 0x0 (null)