[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

• Use SQL-safe aliases for Correlate left inputs instead of exposing internal $cor* names.
• Register correlation ids used by RexSubQuery relations against the enclosing SQL context before visiting the subquery.
• Preserve correlation mappings when visiting Aggregate inputs during RelToSql conversion.

Test

• Added RelToSqlConverterTest.testPostgresqlRoundTripCorrelatedProjectWithSemiJoinRules.
• Asserted the generated SQL no longer contains internal $cor* aliases before the round-trip.
• Verified the retained regression fails on main and passes with this patch.
• Ran:
  JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :core:test --tests org.apache.calcite.rel.rel2sql.RelToSqlConverterTest.testPostgresqlRoundTripCorrelatedProjectWithSemiJoinRules
JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :core:test --tests org.apache.calcite.rel.rel2sql.RelToSqlConverterTest --tests org.apache.calcite.rel.rel2sql.RelToSqlConverterStructsTest
JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :core:checkstyleMain :core:checkstyleTest :core:forbiddenApisMain :core:forbiddenApisTest
JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :piglet:test --tests org.apache.calcite.test.PigRelOpTest
JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :piglet:checkstyleTest :piglet:forbiddenApisTest

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

[github-actions]

This pull request has been marked as stale due to 30 days of inactivity. It will be closed in 90 days if no further activity occurs. If you think that’s incorrect or this pull request requires a review, please simply write any comment. If closed, you can revive the PR at any time and @mention a reviewer or discuss it on the dev@calcite.apache.org list. Thank you for your contributions.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud