FA-42851 / Borrow checking / Open access

A common field prefix suppresses later disjointness · case 01

A common field prefix suppresses later disjointness.

Verified by executionVariant 1 · 13 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The static analyzer mishandles equal projection: a common field prefix suppresses later disjointness.

THE FAILURE

The static analyzer mishandles equal projection: a common field prefix suppresses later disjointness.

Unsuccessful approach: The partial repair uses if x == y and isinstance(x,str): return True, which still violates the stipulated analysis contract.

Case contract

Places are lists of projections: root name, then fields or integer indices. Different roots and unequal fields or known indices are disjoint. A wildcard index ? aliases any index. A union projection | overlaps any sibling. Dereference * conservatively overlaps another projection at that depth. Prefix places overlap; empty denotes no place. Return overlap.

Why this case matters

A finite offline static-analysis model of ownership and borrowing; it does not execute the analyzed program.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(a, b):
    if not a or not b: return False
    if a[0] != b[0]: return False
    for x, y in zip(a[1:], b[1:]):
        if x == y: return True
        if x == '|' or y == '|': return True
        if x == '*' or y == '*': return True
        if x == '?' and isinstance(y, int): continue
        if y == '?' and isinstance(x, int): continue
        if isinstance(x, int) and isinstance(y, int): return False
        if isinstance(x, str) and isinstance(y, str): return False
        return False
    return True
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('absent',solve([],['r']),False)
check('both absent',solve([],[]),False)
check('roots depths',solve(['r'],['s','a']),False)
check('shared prefix',solve(['r','a','b'],['r','a','c']),False)
check('union',solve(['r','|'],['r','a']),True)
check('deref',solve(['r','*'],['r','a']),True)
check('dynamic left',solve(['r','?'],['r',N]),True)
check('dynamic right',solve(['r',N],['r','?']),True)
check('separated indices',solve(['r',N],['r',N+3]),False)
check('adjacent indices',solve(['r',N],['r',N+1]),False)
check('fields',solve(['r','a'],['r','b']),False)
check('parent',solve(['r'],['r','a']),True)
check('same',solve(['r',N],['r',N]),True)
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
absent	`False`	`False`	Passed
both absent	`False`	`False`	Passed
roots depths	`False`	`False`	Passed
shared prefix	`True`	`False`	Failed
union	`True`	`True`	Passed
deref	`True`	`True`	Passed
dynamic left	`True`	`True`	Passed
dynamic right	`True`	`True`	Passed
separated indices	`False`	`False`	Passed
adjacent indices	`False`	`False`	Passed
fields	`False`	`False`	Passed
parent	`True`	`True`	Passed
same	`True`	`True`	Passed

SHA-256 / 05d5a1145f82fda46798ef12c39fb2dde2debce9b22d270f94bca158238aa293

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(a, b):
    if not a or not b: return False
    if a[0] != b[0]: return False
    for x, y in zip(a[1:], b[1:]):
        if x == y and isinstance(x,str): return True
        if x == '|' or y == '|': return True
        if x == '*' or y == '*': return True
        if x == '?' and isinstance(y, int): continue
        if y == '?' and isinstance(x, int): continue
        if isinstance(x, int) and isinstance(y, int): return False
        if isinstance(x, str) and isinstance(y, str): return False
        return False
    return True
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('absent',solve([],['r']),False)
check('both absent',solve([],[]),False)
check('roots depths',solve(['r'],['s','a']),False)
check('shared prefix',solve(['r','a','b'],['r','a','c']),False)
check('union',solve(['r','|'],['r','a']),True)
check('deref',solve(['r','*'],['r','a']),True)
check('dynamic left',solve(['r','?'],['r',N]),True)
check('dynamic right',solve(['r',N],['r','?']),True)
check('separated indices',solve(['r',N],['r',N+3]),False)
check('adjacent indices',solve(['r',N],['r',N+1]),False)
check('fields',solve(['r','a'],['r','b']),False)
check('parent',solve(['r'],['r','a']),True)
check('same',solve(['r',N],['r',N]),True)
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
absent	`False`	`False`	Passed
both absent	`False`	`False`	Passed
roots depths	`False`	`False`	Passed
shared prefix	`True`	`False`	Failed
union	`True`	`True`	Passed
deref	`True`	`True`	Passed
dynamic left	`True`	`True`	Passed
dynamic right	`True`	`True`	Passed
separated indices	`False`	`False`	Passed
adjacent indices	`False`	`False`	Passed
fields	`False`	`False`	Passed
parent	`True`	`True`	Passed
same	`False`	`True`	Failed

SHA-256 / 1e18e2226a7b644ea3d13bef95e1fb3526891963c415ce63039c70d2a9e7f7e1

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 13 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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

The explicitly stated toy language is the complete scope; this is not a production compiler or a claim about Rust semantics. 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 2026-09-29T14:43:56.304675+00:00.

Case digest / a27314a0ee85b3711d48473993000528edb6a58d19466f2afd6cc7468f54a525