HyukjinKwon commented on code in PR #59270:
URL: https://github.com/apache/spark/pull/59270#discussion_r4226361151
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CollationTypeCoercion.scala:
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@@ -113,8 +113,10 @@ object CollationTypeCoercion extends SQLConfHelper {
*
* Literal and Cast: wrap in a new Cast when the CHAR/VARCHAR constraint
* changes so truncation, overflow, and padding stay on the original node.
- * Collation-only changes retarget with `copy(dataType)`, which keeps a
- * non-string Cast child non-string and therefore Default strength.
+ * Collation-only changes retarget with `copy(dataType)` and copy
+ * `USER_SPECIFIED_CAST` (truncation). Do not copy all tags: a stale
+ * `COLLATION_CONTEXT_TAG` would reuse the pre-LCT collation. That keeps
Review Comment:
**Nit (P3):** With the new sentences inserted, `That keeps a non-string Cast
child non-string and therefore Default strength.` now follows the
`COLLATION_CONTEXT_TAG` sentence, so it reads as if not copying the tags is
what keeps Default strength. The strength actually comes from retargeting with
`copy(dataType)` instead of wrapping in a new Cast: `findCollationContext`
derives a Cast's strength from whether its child is a string type, and tags
play no part. Maybe something like:
```
* Collation-only changes retarget with `copy(dataType)`, which keeps a
* non-string Cast child non-string and therefore Default strength. The
copy
* keeps only `USER_SPECIFIED_CAST` (truncation); copying all tags would
reuse
* a stale `COLLATION_CONTEXT_TAG` with the pre-LCT collation.
```
**Verification:**
- **Inspection:** The rewritten scaladoc ties the Default-strength statement
to the copy(dataType) retarget, keeps the tag-copy rationale, contains only
ASCII, and keeps every line within 100 characters.
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