leerho opened a new pull request, #790:
URL: https://github.com/apache/datasketches-java/pull/790
Adds union-result fixtures to the HLL cross-language test. Test-only; no
library code changes.
## Why
The existing HLL fixtures are update sketches only, serialized compact, at a
single lgK. That misses two classes of bugs, and both turned up in September
2026:
- The deferred KxQ rebuild can only be reached through a union, and the
generator creates no unions.
- Flags bit 32 collided between implementations (`REBUILD_CURMIN_NUM_KXQ` in
Java, `FULL_SIZE` in C++). It lives in the flags byte, which nothing inspected,
and only the compact form was ever written.
## What it adds
- `generateUnionBinariesForCompatibilityTesting` writes six files,
`hll{4,6,8}_union_java.sk` (compact) and `hll{4,6,8}_unionupd_java.sk`
(updatable). They come from a union whose inputs span all three curModes, so
coupon updates into a gadget with a pending KxQ rebuild are exercised. One lgK
is enough, because neither defect class depends on lgK. The files go to the
gitignored generated-files directory, so the repository doesn't grow.
- `checkUnionJava`, `checkUnionCpp`, `checkUnionGo` and `checkUnionRust`
share one check body. For each file it asserts that:
- flags bit 32 is never set;
- the compact flag matches the form that was written (HLL_6 and HLL_8 used
to omit it);
- the estimate matches the true count, and is the same for every target
type, since an incorrect KxQ rebuild shifts it.
No C++, Go or Rust generator writes these files yet. Until one does, those
checks warn about the missing files and skip them. Matching generators in the
other repos would be follow-ups.
## Testing
- `-Pcheck_java_files`: generates the files and reads them back, 4/4
`HllSketchCrossLanguageTest` tests pass.
- When it was written, the check was verified by corrupting a fixture:
setting bit 32, or clearing the compact flag, each fails with the intended
message.
- `mvn verify -DskipTests` passes. The default test run is unaffected,
because these groups are excluded by default.
Supersedes the never-opened branch `hll-xlang-fixtures`. This is the same
commit, rebased onto main after #771.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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