FA-90081 / Bytecode virtual machines / Open access
Upvalues: the slot at the closing level stays open · case 01
A closure keeps pointing at a stack slot that was popped and later reused.
ROOT CAUSE
The close loop only closes slots strictly above the level.
THE FAILURE
The close loop only closes slots strictly above the level.
Unsuccessful approach: Closing one level lower also detaches a local that is still live in the enclosing scope.
Case contract
A register/stack VM with open and closed upvalues. ["local", v] pushes a slot; ["set", s, v] and ["get", s] access slots; ["closure", id, [slots]] captures slots, reusing the existing open upvalue for a slot so closures share variables; ["uset"/"uget", id, k, (v)] access the k-th upvalue, going to the stack slot while open and to the upvalue's own cell once closed; ["close", level] closes every open upvalue whose slot >= level (copying the slot value) and truncates the stack to level. Accessing a vanished slot appends "dangling-slot" and stops.
Why this case matters
Closure capture and upvalue closing are subtle lifetime transitions in register-based VMs.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(events):
stack = []
open_uv = []
closures = {}
out = []
try:
for ev in events:
op = ev[0]
if op == 'local':
stack.append(ev[1])
elif op == 'set':
stack[ev[1]] = ev[2]
elif op == 'get':
out.append(stack[ev[1]])
elif op == 'closure':
ups = []
for s in ev[2]:
uv = next((u for u in open_uv if u['slot'] == s), None)
if uv is None:
uv = {'slot': s, 'open': True, 'value': None}
open_uv.append(uv)
ups.append(uv)
closures[ev[1]] = ups
elif op == 'uset':
uv = closures[ev[1]][ev[2]]
if uv['open']:
stack[uv['slot']] = ev[3]
else:
uv['value'] = ev[3]
elif op == 'uget':
uv = closures[ev[1]][ev[2]]
out.append(stack[uv['slot']] if uv['open'] else uv['value'])
elif op == 'close':
level = ev[1]
for uv in open_uv:
if uv['slot'] > level:
uv['value'] = stack[uv['slot']]
uv['open'] = False
open_uv = [u for u in open_uv if u['open']]
del stack[level:]
except IndexError:
out.append('dangling-slot')
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('two closures share one open upvalue',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1]],),
[6, 6]),
('closing a scope keeps closures linked',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[6, 6, 0]),
('regression: new local reusing a closed slot',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 78],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[6, 6, 0, 78, 0]),
('open upvalue tracks later stack writes',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 78],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 3],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[6, 6, 0, 78, 0, 10, 3, 78]),
('slot reuse after closing everything',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 78],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 3],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[6, 6, 0, 78, 0, 10, 3, 78, 109, 3, 109]),
('closure over only the outer local',
([['local', 1], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[1, 2]),
('control: plain locals', ([['local', 1], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 1])],
[('two closures share one open upvalue',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1]],),
[7, 7]),
('closing a scope keeps closures linked',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[7, 7, 0]),
('regression: new local reusing a closed slot',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 79],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[7, 7, 0, 79, 0]),
('open upvalue tracks later stack writes',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 79],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 6],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[7, 7, 0, 79, 0, 20, 6, 79]),
('slot reuse after closing everything',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 79],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 6],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[7, 7, 0, 79, 0, 20, 6, 79, 109, 6, 109]),
('closure over only the outer local',
([['local', 2], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[2, 2]),
('control: plain locals', ([['local', 2], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 2])],
[('two closures share one open upvalue',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1]],),
[8, 8]),
('closing a scope keeps closures linked',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[8, 8, 0]),
('regression: new local reusing a closed slot',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 80],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[8, 8, 0, 80, 0]),
('open upvalue tracks later stack writes',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 80],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 9],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[8, 8, 0, 80, 0, 30, 9, 80]),
('slot reuse after closing everything',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 80],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 9],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[8, 8, 0, 80, 0, 30, 9, 80, 109, 9, 109]),
('closure over only the outer local',
([['local', 3], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[3, 2]),
('control: plain locals', ([['local', 3], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 3])],
[('two closures share one open upvalue',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1]],),
[9, 9]),
('closing a scope keeps closures linked',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[9, 9, 0]),
('regression: new local reusing a closed slot',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 81],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[9, 9, 0, 81, 0]),
('open upvalue tracks later stack writes',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 81],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 12],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[9, 9, 0, 81, 0, 40, 12, 81]),
('slot reuse after closing everything',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 81],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 12],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[9, 9, 0, 81, 0, 40, 12, 81, 109, 12, 109]),
('closure over only the outer local',
([['local', 4], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[4, 2]),
('control: plain locals', ([['local', 4], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 4])],
[('two closures share one open upvalue',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1]],),
[10, 10]),
('closing a scope keeps closures linked',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[10, 10, 0]),
('regression: new local reusing a closed slot',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 82],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[10, 10, 0, 82, 0]),
('open upvalue tracks later stack writes',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 82],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 15],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[10, 10, 0, 82, 0, 50, 15, 82]),
('slot reuse after closing everything',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 82],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 15],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[10, 10, 0, 82, 0, 50, 15, 82, 109, 15, 109]),
('closure over only the outer local',
([['local', 5], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[5, 2]),
('control: plain locals', ([['local', 5], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 5])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| two closures share one open upvalue | [6, 6] | [6, 6] | Passed |
| closing a scope keeps closures linked | [6, 6, 'dangling-slot'] | [6, 6, 0] | Failed |
| regression: new local reusing a closed slot | [6, 6, 'dangling-slot'] | [6, 6, 0, 78, 0] | Failed |
| open upvalue tracks later stack writes | [6, 6, 'dangling-slot'] | [6, 6, 0, 78, 0, 10, 3, 78] | Failed |
| slot reuse after closing everything | [6, 6, 'dangling-slot'] | [6, 6, 0, 78, 0, 10, 3, 78, 109, 3, 109] | Failed |
| closure over only the outer local | [2, 2] | [1, 2] | Failed |
| control: plain locals | [4, 1] | [4, 1] | Passed |
SHA-256 / c3c3d20d1565222353400f622190288aa9ecfde2a94eda54bd4787c52c082b9f
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(events):
stack = []
open_uv = []
closures = {}
out = []
try:
for ev in events:
op = ev[0]
if op == 'local':
stack.append(ev[1])
elif op == 'set':
stack[ev[1]] = ev[2]
elif op == 'get':
out.append(stack[ev[1]])
elif op == 'closure':
ups = []
for s in ev[2]:
uv = next((u for u in open_uv if u['slot'] == s), None)
if uv is None:
uv = {'slot': s, 'open': True, 'value': None}
open_uv.append(uv)
ups.append(uv)
closures[ev[1]] = ups
elif op == 'uset':
uv = closures[ev[1]][ev[2]]
if uv['open']:
stack[uv['slot']] = ev[3]
else:
uv['value'] = ev[3]
elif op == 'uget':
uv = closures[ev[1]][ev[2]]
out.append(stack[uv['slot']] if uv['open'] else uv['value'])
elif op == 'close':
level = ev[1]
for uv in open_uv:
if uv['slot'] >= level - 1:
uv['value'] = stack[uv['slot']]
uv['open'] = False
open_uv = [u for u in open_uv if u['open']]
del stack[level:]
except IndexError:
out.append('dangling-slot')
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('two closures share one open upvalue',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1]],),
[6, 6]),
('closing a scope keeps closures linked',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[6, 6, 0]),
('regression: new local reusing a closed slot',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 78],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[6, 6, 0, 78, 0]),
('open upvalue tracks later stack writes',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 78],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 3],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[6, 6, 0, 78, 0, 10, 3, 78]),
('slot reuse after closing everything',
([['local', 10],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 6],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 78],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 3],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[6, 6, 0, 78, 0, 10, 3, 78, 109, 3, 109]),
('closure over only the outer local',
([['local', 1], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[1, 2]),
('control: plain locals', ([['local', 1], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 1])],
[('two closures share one open upvalue',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1]],),
[7, 7]),
('closing a scope keeps closures linked',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[7, 7, 0]),
('regression: new local reusing a closed slot',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 79],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[7, 7, 0, 79, 0]),
('open upvalue tracks later stack writes',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 79],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 6],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[7, 7, 0, 79, 0, 20, 6, 79]),
('slot reuse after closing everything',
([['local', 20],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 7],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 79],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 6],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[7, 7, 0, 79, 0, 20, 6, 79, 109, 6, 109]),
('closure over only the outer local',
([['local', 2], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[2, 2]),
('control: plain locals', ([['local', 2], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 2])],
[('two closures share one open upvalue',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1]],),
[8, 8]),
('closing a scope keeps closures linked',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[8, 8, 0]),
('regression: new local reusing a closed slot',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 80],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[8, 8, 0, 80, 0]),
('open upvalue tracks later stack writes',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 80],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 9],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[8, 8, 0, 80, 0, 30, 9, 80]),
('slot reuse after closing everything',
([['local', 30],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 8],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 80],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 9],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[8, 8, 0, 80, 0, 30, 9, 80, 109, 9, 109]),
('closure over only the outer local',
([['local', 3], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[3, 2]),
('control: plain locals', ([['local', 3], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 3])],
[('two closures share one open upvalue',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1]],),
[9, 9]),
('closing a scope keeps closures linked',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[9, 9, 0]),
('regression: new local reusing a closed slot',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 81],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[9, 9, 0, 81, 0]),
('open upvalue tracks later stack writes',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 81],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 12],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[9, 9, 0, 81, 0, 40, 12, 81]),
('slot reuse after closing everything',
([['local', 40],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 9],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 81],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 12],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[9, 9, 0, 81, 0, 40, 12, 81, 109, 12, 109]),
('closure over only the outer local',
([['local', 4], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[4, 2]),
('control: plain locals', ([['local', 4], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 4])],
[('two closures share one open upvalue',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1]],),
[10, 10]),
('closing a scope keeps closures linked',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1]],),
[10, 10, 0]),
('regression: new local reusing a closed slot',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 82],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1]],),
[10, 10, 0, 82, 0]),
('open upvalue tracks later stack writes',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 82],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 15],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0]],),
[10, 10, 0, 82, 0, 50, 15, 82]),
('slot reuse after closing everything',
([['local', 50],
['local', 0],
['closure', 'f', [0, 1]],
['closure', 'g', [1]],
['uset', 'f', 1, 10],
['uget', 'g', 0],
['get', 1],
['close', 1],
['uset', 'g', 0, 0],
['uget', 'f', 1],
['local', 82],
['closure', 'h', [1]],
['uget', 'h', 0],
['uget', 'f', 1],
['uget', 'f', 0],
['set', 0, 15],
['uget', 'f', 0],
['close', 0],
['uget', 'h', 0],
['local', 109],
['closure', 'k', [0]],
['uget', 'k', 0],
['uget', 'f', 0],
['get', 0]],),
[10, 10, 0, 82, 0, 50, 15, 82, 109, 15, 109]),
('closure over only the outer local',
([['local', 5], ['closure', 'c', [0]], ['close', 0], ['local', 2], ['uget', 'c', 0], ['get', 0]],),
[5, 2]),
('control: plain locals', ([['local', 5], ['local', 2], ['set', 1, 4], ['get', 1], ['get', 0]],), [4, 5])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| two closures share one open upvalue | [6, 6] | [6, 6] | Passed |
| closing a scope keeps closures linked | [6, 6, 0] | [6, 6, 0] | Passed |
| regression: new local reusing a closed slot | [6, 6, 0, 78, 0] | [6, 6, 0, 78, 0] | Passed |
| open upvalue tracks later stack writes | [6, 6, 0, 78, 0, 10, 10, 78] | [6, 6, 0, 78, 0, 10, 3, 78] | Failed |
| slot reuse after closing everything | [6, 6, 0, 78, 0, 10, 10, 78, 109, 10, 109] | [6, 6, 0, 78, 0, 10, 3, 78, 109, 3, 109] | Failed |
| closure over only the outer local | [1, 2] | [1, 2] | Passed |
| control: plain locals | [4, 1] | [4, 1] | Passed |
SHA-256 / 05ba1bc8e9e03c09cdf8168d4883bbfe123732a82cc5ae18103e5f5f9a214e0e
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 7 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.
Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.
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Sign in to the archive ↗Verification & scope
A deterministic, bounded teaching model of one bytecode virtual machine mechanism with a stipulated instruction encoding; it is not a production VM and claims no conformance to any real specification. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:51:23.605122+00:00.
Case digest / fd05679fff844b2a9ad2f27b2fdc359ac30a15f427fe7797c4136db07448d7b0