[CALCITE-7440] Preserve correlated scope mapping in RelToSqlConverter

[bvolpato]

Summary

RelToSqlConverter can lose correlation context during PostgreSQL round-trip conversion after the semi-join rewrite pipeline, causing variable $cor1 is not found.

Reproduction query

WITH product_keys AS (
  SELECT p."product_id",
         (SELECT MAX(p3."product_id")
          FROM "foodmart"."product" p3
          WHERE p3."product_id" = p."product_id") AS "mx"
  FROM "foodmart"."product" p
)
SELECT DISTINCT pk."product_id"
FROM product_keys pk
LEFT JOIN "foodmart"."product" p2 USING ("product_id")
WHERE pk."product_id" IN (
  SELECT p4."product_id"
  FROM "foodmart"."product" p4
)

Reproducer rules

RuleSets.ofList(
    CoreRules.FILTER_SUB_QUERY_TO_MARK_CORRELATE,
    CoreRules.PROJECT_SUB_QUERY_TO_MARK_CORRELATE,
    CoreRules.MARK_TO_SEMI_OR_ANTI_JOIN_RULE,
    CoreRules.SEMI_JOIN_JOIN_TRANSPOSE)

Error before this PR

java.lang.NullPointerException: variable $cor1 is not found
  at org.apache.calcite.rel.rel2sql.SqlImplementor.getAliasContext(SqlImplementor.java:1590)

Fix

• Preserve correlation mappings when visiting Aggregate inputs during RelToSql conversion.
• Keep the alias-context fallback scoped to the empty-map case only.

Test

• Added RelToSqlConverterTest.testPostgresqlRoundTripCorrelatedProjectWithSemiJoinRules
• Verified the retained regression fails on main and passes with this patch
• Ran:
  JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :core:test --tests org.apache.calcite.rel.rel2sql.RelToSqlConverterTest.testPostgresqlRoundTripCorrelatedProjectWithSemiJoinRules

Disclaimer

The changes were done with the assistance of Codex (gpt-5.3-codex) in response to an actual bug when using Calcite in production. The changes were manually verified prior to sending this to review.

[bvolpato]

Thanks for the review! Updated this PR with both requested changes:

Reduced the regression to the minimal reproducer on main (empty rules was a mistake):

• FILTER_SUB_QUERY_TO_MARK_CORRELATE
• PROJECT_SUB_QUERY_TO_MARK_CORRELATE
• MARK_TO_SEMI_OR_ANTI_JOIN_RULE
• SEMI_JOIN_JOIN_TRANSPOSE

Added a plain round-trip test without extra rules:

• testPostgresqlRoundTripCorrelatedProject

Both new/updated tests pass locally in this branch.

[xiedeyantu]

Could we please consider @asolimando 's suggestion in Jira? Personally, I don't think this particular fix is ​​entirely appropriate. Incidentally, regarding the structure of the test case: you might want to refer to other examples for guidance. Please avoid using try-catch blocks; if an error occurs, it should be allowed to surface naturally.

[bvolpato]

@xiedeyantu I addressed the test-structure part of your note:

• removed the try-catch from testPostgresqlRoundTripCorrelatedProjectWithSemiJoinRules
• updated the PR description so it matches the retained reproducer and current fix

On the Jira alias suggestion: I considered it, but I kept this PR scoped to the failure mode reproduced here. The retained regression still fails on main and passes with this patch, while changing alias generation in visit(Correlate) would be a broader behavior change than the NPE fix in this PR.

If you want, I can also split out the alias-cleanup direction as a separate follow-up.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
86.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud