Fix the OWritesBench compilation on Scala 2

[linyiru]

Pull Request Checklist

• Have you read through the contributor guidelines?
• Have you squashed your commits?
• Have you added copyright headers to new files? (no new files)
• Have you updated the documentation? (benchmarks only, nothing to document)
• Have you added tests for any changed functionality? (benchmarks only)

Purpose

On main, the benchmarks project does not compile on Scala 2.12 or 2.13:

[error] OWritesBench.scala:60:12: diverging implicit expansion for type play.api.libs.json.Writes[T1]
[error] starting with method Tuple22W in trait GeneratedWrites
[error]     Writes.genericMapWrites.writes(employeeIdMap)

and the same at line 64 for Writes.keyMapWrites.writes(scoreMap). Scala 3.3 compiles it. Because the default scalaVersion is 2.13, benchmarks / Jmh / run fails for every benchmark, not just this one.

This passes the type arguments explicitly: genericMapWrites[String, Map] and keyMapWrites[Int, Double, Map].

The file is also reformatted with scalafmt. It had not been formatted since it was added, because validateCode does not check the benchmarks project (which is also why CI did not catch the compile error).

Checked locally (JDK 17): +benchmarks/Jmh/compile passes on 2.12.21, 2.13.18 and 3.3.8, and benchmarks/scalafmtCheckAll passes. On main, benchmarks/compile fails on 2.12.21 and 2.13.18 and passes on 3.3.8.

References

Found while benchmarking append for the review of #1482 (#1482 (comment)). OWritesBench was added in #1430.

AI disclosure: I directed and verified this work; Claude Code (Claude Opus) assisted with the investigation, the patch and this description.

🤖 Generated with Claude Code

[mergify]

Queued — the merge queue status continues in this comment ↓.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-10-07 13:49 UTC · Rule: default · triggered by @cchantep with the merge queue checkbox
• ✅ Checks passed · on draft merge queue: checking #1485 on main (6801bab) #1486
• ✅ Merged — 2026-10-07 13:58 UTC · at 2455a5a7f93ab755f6618bf4b9809278cde6de44 · merge

This pull request spent 9 minutes 21 seconds in the queue, including 8 minutes 53 seconds running CI.

Required conditions to merge

• github-review-approved [🛡 GitHub branch protection]
  • Fix the OWritesBench compilation on Scala 2 #1485
• any of [🛡 GitHub branch protection]:
  • check-success = Finish / Ready To Merge
  • check-neutral = Finish / Ready To Merge
  • check-skipped = Finish / Ready To Merge