From 3f906d03262150892e2297e621bfc56e425ef142 Mon Sep 17 00:00:00 2001 From: Paul Buetow Date: Mon, 6 Jul 2026 10:32:34 +0300 Subject: Close verification-coverage gaps; harness finds two more bugs Extends the verification harness from sorts-only to the whole repo, and in doing so surfaces two further latent bugs (on top of the earlier hash-shift one): Bugs found and fixed: - queue/elementarypriority.go: max() seeded at the zero value, so an all-negative queue reported a phantom max of 0 and DeleteMax returned/removed the wrong element. Caught by the new queue permutation property (testing/quick generates negatives; the old test data never did). Seed from a[0] instead. - sort/sleep.go: result built on NewArrayList(len(a)) -- a slice of that LENGTH (len(a) zeros) -- then appended to, yielding double-length output with leading zeros. The old .Sorted()-only test passed because zeros-then-ascending is sorted. Caught by the new Sleep permutation check. Build from an empty slice. Coverage added: - queue/property_test.go: ordering + permutation (completeness) for both queues. - TestSleepSort now also checks permutation, not just Sorted(). - docs/verification.md: paper proofs for all search/set structures (Elementary, Hash, BST, red-black BST invariants, GoMap) and both priority queues. - formal/tla/ParallelSort.tla: exhaustive fork/join model of ParallelMerge/ ParallelQuick -- disjoint write-ranges (no data race) + termination. Wired into make verify-model. - formal/selection.go: second Gobra proof (memory safety + sortedness). Wired into make verify-formal. - docs/case-study-bugs-found.md: extensive write-up of all three bugs, how each was caught, why the old tests missed it, and the fix (supersedes the earlier single-bug case study). Co-Authored-By: Claude Opus 4.8 --- queue/elementarypriority.go | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'queue/elementarypriority.go') diff --git a/queue/elementarypriority.go b/queue/elementarypriority.go index 391d948..9cb9e54 100644 --- a/queue/elementarypriority.go +++ b/queue/elementarypriority.go @@ -50,6 +50,13 @@ func (q *ElementaryPriority[T]) Clear() { } func (q *ElementaryPriority[T]) max() (ind int, max T) { + // Seed from the first element, not the zero value of T: for a queue holding + // only negative values nothing is greater than 0, so a zero seed would + // wrongly report index 0 / value 0 (an element not even in the queue). + if len(q.a) == 0 { + return 0, 0 + } + ind, max = 0, q.a[0] for i, a := range q.a { if a > max { ind, max = i, a -- cgit v1.2.3