Alwaysgaurav1 opened a new pull request, #69553:
URL: https://github.com/apache/airflow/pull/69553
### Description
The `GET /execution/xcoms/{dag_id}/{run_id}/{task_id}/{key}/slice` endpoint
translates Python-style slicing into SQLAlchemy `.slice(start, stop)` calls.
However, when `start >= 0` and `stop < 0` (or vice versa), the `stop` value is
adjusted using the total count of rows. After this adjustment, the bounds can
"cross" (i.e., `stop <= start` for forward slices), resulting in a negative
`LIMIT` value being passed to the database — which either returns wrong rows or
causes a database error.
### Fix
This PR adds explicit guards after the count-based adjustment in both the
`start >= 0` and `start < 0` branches:
- If the adjusted bounds have crossed for a forward slice (`step >= 0` and
`stop <= start`), return an empty list immediately.
- If the adjusted bounds have crossed for a reverse slice (`step < 0` and
`start < stop`), return an empty list immediately.
This matches standard Python slice behavior where crossed bounds produce an
empty sequence (e.g., `[1,2,3][5:2] == []`).
All 18 existing slice tests continue to pass.
Closes: #69204
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