xiangfu0 opened a new pull request, #18837:
URL: https://github.com/apache/pinot/pull/18837
## Summary
This PR addresses the follow-up from #18835 by removing
`Collections.singletonList(...)` usage from the Java source tree and parser
template, then banning new usage through Checkstyle.
Changes:
- Replaced `Collections.singletonList(...)` with `List.of(...)` across the
repo.
- Preserved single-null-list test semantics with `Arrays.asList((Object)
null)` where `List.of(null)` would throw `NullPointerException`.
- Added a Checkstyle `RegexpSingleline` guard to reject future
`Collections.singletonList(` usage.
## Why
`Collections.singletonList()` accepts null elements, while modern immutable
list construction with `List.of()` rejects nulls. The repo-wide migration makes
single-element immutable list creation consistent and lets Checkstyle prevent
regressions.
## User Manual / Contributor Guidance
For new Pinot code, use `List.of(value)` for non-null single-element lists.
If a test intentionally needs a one-element list containing `null`, use an
explicit null-preserving list construction such as `Arrays.asList((Object)
null)` and keep the intent local to the test.
## Sample Table Config / Queries
No table config or query syntax changes are introduced. Query behavior is
unchanged; existing empty-aggregation/null-result test cases continue to cover
the user-visible query results that motivated #18835.
## Validation
- `rg -n
"Collections\\.singletonList|List\\.(<[^>]+>)?of\\(\\s*(\\([^)]*\\)\\s*)?null\\s*\\)"
--glob '!target/**' --glob '!kb/**' --glob '!config/checkstyle.xml' --glob
'*.java'`
- `./mvnw spotless:apply`
- `./mvnw checkstyle:check`
- `git diff --check`
- `./mvnw -DskipTests test-compile`
- The initial root run hit a local Maven cache miss for `jsr305` at
`pinot-s3`; after refreshing the dependency cache, `./mvnw -DskipTests
test-compile -rf :pinot-s3` passed through the remaining modules.
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