Integrated: 2591: Improve auto labeler

[Zhao Song]

On Tue, 23 Sep 2025 16:47:33 GMT, Zhao Song <zsong at openjdk.org> wrote:

> After [SKARA-2588](https://bugs.openjdk.org/browse/SKARA-2588) is deployed, users are complaining about the behavior of auto labeler.
> 
> After discussion with Erik, we propose the following behavior for the auto labeler:
>  1. The auto labeler will never remove labels that have already been added.
>  2. The only case in which the auto labeler upgrades labels to group labels is when it detects a bunch of new labels to add. In this case, it will attempt to update the labels to group labels.
>  3. Users can add any labels they want.
>  
>  Example:
> 1. In the initial labeling, the auto labeler adds “hotspot-runtime” to the PR.
>       (Current labels: “hotspot-runtime”)
> 2. The user pushes three commits that touch “hotspot-gc” and “hotspot-jfr”. The auto labeler upgrades these to the group label “hotspot” and adds it to the PR.
>      (Current labels: “hotspot-runtime”, “hotspot”)
> 3. Later, the user pushes a new commit touches only “hotspot-gc”. The auto labeler will not add “hotspot-gc” to the PR since “hotspot” label is already there.
>      (Current labels: “hotspot-runtime”, “hotspot”)

This pull request has now been integrated.

Changeset: 735a6b08
Author:    Zhao Song <zsong at openjdk.org>
URL:       https://git.openjdk.org/skara/commit/735a6b082e371e75fab5a6939de126905ab48e7c
Stats:     198 lines in 8 files changed: 115 ins; 40 del; 43 mod

2591: Improve auto labeler

Reviewed-by: erikj

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PR: https://git.openjdk.org/skara/pull/1741