Evidenceqs-514
Duplicates set to last, should not apply to arrays without index
qs#514, at commit 9d441d2. A closed issue from a repository Credda did not choose.
LIVE2026-09-20
RIGHT_FAILUREexecuted against the upstream checkout.
- Outcome
- PARTIALLY_VERIFIED
- Wall time
- 271.9s
- Checks
- 5 passed of 5 applicable
RECORDED
NOT_GRADEDgraded from the transcript committed with this case.
- Outcome
- not recorded
- Checks
- none run
01The signal
The report, exactly as it was filed.
Nothing paraphrased or cleaned up. The mess is the thing under test.
Duplicates set to last, should not apply to arrays without index
Hi!
Maybe I'm mistaken, but I think when `duplicates` is set to `"last"`, it should not apply to arrays without indices:
`qs.parse("a=1&a=2&b[]=1&b[]=2", {duplicates: "last"})`
results in
`{ a: '2', b: [ '2' ] }`
Where `a` is correct, but `b` was not what I expected.- Repository
- ljharb/qs
- Issue
- #514
- Commit
- 9d441d270486c3cc77f17289a9e0921c0f742aff
- Why this commit
- The first parent of the fix commit 88e15636da953397262bd3014ab8b0d17d5c8039, which GitHub binds to this issue via CLOSED_EVENT_COMMIT. Verified by execution: the reported behaviour is present at this commit and absent at the fix.
- How the text was obtained
- Fetched verbatim via the GitHub GraphQL API. Title on the first line, body unmodified below it. Nothing was paraphrased, cleaned up, or supplemented.
- Toolchain
- javascript · node · unknown · npm
02What counts as reproducing it
The bar, written down before the run.
- Symptom
- qs.parse("a=1&a=2&b[]=1&b[]=2", {duplicates: "last"}) produces { a: '2', b: [ '2' ] }; the fix makes it produce { a: '2', b: [ '1', '2' ] }.
- Expression
- qs.parse("a=1&a=2&b[]=1&b[]=2", {duplicates: "last"})
- Reported output
- { a: '2', b: [ '2' ] }
- Where that came from
- Proposed by a model reading this report and nothing else -- it never saw the repository or the fix commit -- and read back as a claim by the same parser the harvest uses, SAME_LINE form: `qs.parse("a=1&a=2&b[]=1&b[]=2", {duplicates: "last"}) //=> { a: '2', b: [ '2' ] }`. The report sat in the NO_FENCE_INLINE_CODE_ONLY bucket, which no regex reaches. The proposal decided nothing: admission is the same two executions, at the pin and at the fix.
03What happened
The live run reproduced the reported failure.
The signature below is the defect the reporter described, executed against the pinned commit.
`qs.parse("a=1&a=2&b[]=1&b[]=2", {duplicates: "last"})` still produces { a: '2', b: [ '2' ] } (read { a: '2', b: [ '2' ] })The LIVE grading as emitted. A check that did not apply is never shown as a pass.
| Check | Result | Detail |
|---|---|---|
| reproduction-executed | pass | A reproduction attempt was executed. |
| signature-captured | pass | `qs.parse("a=1&a=2&b[]=1&b[]=2", {duplicates: "last"})` still produces { a: '2', b: [ '2' ] } (read { a: '2', b: [ '2' ] }) |
| right-failure | pass | Reproduced the reported failure: qs.parse("a=1&a=2&b[]=1&b[]=2", {duplicates: "last"}) produces { a: '2', b: [ '2' ] }; the fix makes it produce { a: '2', b: [ '1', '2' ] }. |
| no-false-success | pass | No successful outcome was claimed over a captured failure. |
| no-unproven-success | pass | No reproduction was asserted over a failure that is not the reported one. |
bench/external/scorecard.json, the run of 2026-09-20 against all 158 upstream checkouts.
The same case, graded from the transcript recorded .
The grading the benchmark gate runs on. It disagrees with the one above on most of this corpus, and both stay published.
Check it yourself
Everything here is downstream of a public commit.
Clone it, check out 9d441d2, run the report through the CLI the way the study did.
git clone https://github.com/ljharb/qs git checkout 9d441d270486c3cc77f17289a9e0921c0f742aff npm install CREDDA_PROVIDER=heuristic \ npx tsx apps/cli/src/main.ts fix <repo-path> @<issue-file> --no-color