Honor set-multimap hash-collision node invariant during removals #42
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Hash-collision nodes were able to underflow upon removals and store a single remaining (non-colliding) key. This violated the canonical representation assumption and led to erroneously skipping compaction.
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Oh that's quite elegant with the invariants! Writing the test manually proved very difficult for me ;-) |
jurgenvinju
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Jan 23, 2026
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- love the way the invariants can catch the issue from the existing specification tests
- I knew some compaction was missing somewhere, but I would never have found this elegant solution.
Thanks @msteindorfer
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We should probably add the gradle test run to the github actions. I've yet to figure out how to let mvn run all the tests. |
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…ce/vallang#308 via the capsule PR of usethesource/capsule#42
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Context
Hash-collision nodes were able to underflow upon removals and store a single remaining (non-colliding) key. This violated the canonical representation assumption and led to erroneously skipping compaction. This PR adds invariant checking and ensures that invariants are honored during removals.
Triaging
With the information provided in #41, I was able to pinpoint the issue after attaching a debugger to the Rascal REPL and execute the provided equality comparison. It turned out that an invariant assertion was missing in the set-multi map (that was now inserted), although it was present in the set and map data types.
Once the invariant check was added, the property-based test suite flagged the invariant violation. Hence the coverage of generated inputs is sufficiently covers scenarios that elicit the behaviour reported in #41:
Validating
With the fix present in this PR, the property-based test suite does not show any invariant violations for set-multimap hash-collision nodes any more.