Fix reversed direction examples in FanOutMapper docs#69313
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The FanOutMapper docstrings in core and the Task SDK both described Window.Direction.FORWARD as producing a trailing/next period, but FORWARD (the default) actually yields the period starting at the upstream key; BACKWARD yields the trailing period ending at it. Both copies are corrected and now match each other.
Lee-W
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July 3, 2026 09:03
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Jul 7, 2026
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Hi maintainer, this PR was merged without a milestone set.
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Backport successfully created: v3-3-testNote: As of Merging PRs targeted for Airflow 3.X In matter of doubt please ask in #release-management Slack channel.
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) (cherry picked from commit 7311379) Co-authored-by: Wei Lee <weilee.rx@gmail.com>
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) (cherry picked from commit 7311379) Co-authored-by: Wei Lee <weilee.rx@gmail.com>
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) (#69511) Co-authored-by: Wei Lee <weilee.rx@gmail.com>
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) (#69511) Co-authored-by: Wei Lee <weilee.rx@gmail.com>
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Why
Window.Direction.FORWARD(the default) yields the period starting at the upstream key — the period it represents — whileBACKWARDyields the trailing period ending at the key. The docstrings described it the other way around: they claimedFORWARDproduced the trailing/"next" period, and the code examples setdirection=Window.Direction.FORWARDto get the trailing window. An author following either docstring would pick the opposite direction from what they intended.What
airflow-core/src/airflow/partition_mappers/temporal.pyandtask-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.pyto state thatFORWARDstarts at the upstream key andBACKWARDtrails it.Window.Direction.BACKWARDfor the trailing period, and corrected the accompanying comments (e.g. "the 7 days the upstream Monday represents" vs. "the 7 days ending at the upstream Monday").Was generative AI tooling used to co-author this PR?
{pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.