Repository navigation
Nullability: a demand overruled by a null-tolerant analysed override (Joiner's useForNull) #85
Description
#68's tolerance walk fails on a parameter the callee demands non-null (demanded(m, pi)). The call may be virtual: guava's Joiner.appendTo calls toString(parts.next()); the base Joiner.toString(part) does requireNonNull(part), but the useForNull override reads part and demands nothing (part == null ? nullText : ...). For the Kotlin printer a parameter must be nullable when some dispatch target accepts null, so a demand in the declaring method should be overruled by an analysed override that reads the parameter and demands nothing of it.
The rule was tried (reverted, not in any commit): in tolerates(), case ParameterInfo, if (demanded(..)) { if (toleratedByOverride(m, pi)) continue; return false; }, with implementations.get(m) giving the overrides. It did not decide Joiner on its own because the walk never reaches toString: nothing in the successors map connects the anonymous AbstractList.get()'s return to appendTo's parts.next(). That hop is the library's element slot (Iterable<E>'s Arg(.., 0) / iterator().next()). Two parts, then:
- an edge from the return of an override of
AbstractList.get/Iterator.nextto the element slot of the object (the anonymous class instance), so thatiterable(..)'s return carries first/second/rest as elements; - the override rule above, gated.
Until then the return of a library override is a stop (gate NOLIBRARYRETURN, ws/maddi-null-libreturn, fb21cf26): tolerant by construction, which is what guava's annotations say but not a derivation.
Check against #68's exclusions: hook (an empty override is no evidence: read(o, op) handles it) and overridesAnalysed.
Found while fixing the #72 4a follow-ups (the switch fork exposed Joiner's first/second/rest as UNSAFE in the oracle).
Activity
bnaudts commentedon Nov 4, 2026
Implemented in 9c250e5 (ws/maddi-null, not merged yet), both parts:
GraphCompletion.overrideReturnsIntoSlotsadds an edge from an anonymous class's override of a library superclass method that returns a type parameter (AbstractList.get→E) to the anonymousthis's slot for that parameter. That slot already reached what the creation is assigned to (MethodWalker.anonymousThisTarget).Contracts.overrideContractsno longer holds such a return non-null (overridesKotlinNonNullReturnhad made it a contract). And the closure lets the value into the slot as content rather than as an asserted write (NullGraph.elementHandedOut). Otherwise the result would beget(): Any?overridingAbstractList<Any>.get(): Any.NOOVERRIDERETURNSLOTS.NOOVERRIDETOLERATES.A third change was needed for the walk to get through:
Tolerance.declaredSlotno longer ends the walk at an anonymous class's type argument or at a private method's return slot. Neither is a declaration a caller sees. GateNOINTERNALSLOTS.Result (
TestTolerance.toleranceThroughOverrideAndAnonymousElement, Kotlin policy):join(first, second, rest): first and second areObject?, rest isObject[].$1.get(int)isObject?anditerable(..)isIterable<Object?>.useForNulloverride, first staysObject, as it does with either of the two main gates set.Object: the walk stopped at the contract on get's return.The analyzer suite passes (683, 0 failed). Pending: a guava/langchain4j printer comparison with all three gates set.
Nullability: a demand overruled by a null-tolerant override, through …
bnaudts commentedon Nov 5, 2026
Two regressions from 9c250e5, both fixed on ws/maddi-null (measured by maddi-all on laser1, lanes o/a/c, against devel 4179d4e):
NOOVERRIDECYCLES). guava'sOrdering.min(Iterable)demands its argument;ReverseOrderingandReverseNaturalOrderingonly forward it tomax(Iterable), whose overrides forward it back. Every override counted as tolerating, and none reads null. Effect: 62 oracle NOISE rows;ReverseOrdering.ktandReverseNaturalOrdering.ktout of the J2K bytecode. Now an override overrules a demand only when it compares the parameter with null, or when its own walk ends tolerant (least fixpoint).NOPRIVATECREATOR). jenkins' publicRingBufferLogHandler.getView(): the nullable element reachedSlaveLogFetcher extends MasterToSlaveCallable<List<LogRecord>, …>and an anonymousFeedAdapter<LogRecord>, which the family does not rewrite. That gave 3 Kotlin type errors. The slot now applies only to an anonymous object created in a private method; guava'sJoiner.iterableis private.Joiner.ktstill printsobject : AbstractList<Any?>(). Analyzer suite 686/0; one flaky run of TestStaticAndSelfFields is filed as #95.bnaudts commentedon Nov 5, 2026
Merged into devel in dd13ad9: the original fix 9c250e5 and both regression fixes, d5f1cfd and 6a84d39. The guava oracle ratchet moves to 1,779 noise in a follow-up commit.
Nullability: a cycle of delegating overrides does not overrule a dema…
Nullability: an override return slot only for an anonymous object cre…
Nullability oracle ratchet: 1,779 noise on devel (#85)