Merging main into PR causes incorrect labeling

[jamesmehorter]

Description:
PR 1 is opened which has no changes matching patterns in labeler.yml, and as expected receives no labels, good. Meanwhile, PR 2 (which did match and receive a label, also good) is merged into main. Afterwards, merging main into PR 1 causes labeler to apply the same labels applied to PR 2, bad.

Action version:
v4

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Repro steps:

1. Create PR 1 which matches no rules in labeler.yml, confirm no labels are applied to PR 1
2. Create PR 2 which does match rules in labeler.yml, confirm labels are applied to PR 2
3. Merge PR 2 into main
4. Merge main into PR 1, observe that PR 2s labels are applied to PR 1

Expected behavior:
Upon 4 above, no labels are applied to PR 1

Actual behavior:
Upon 4 above, labels are applied to PR 1

[jamesmehorter]

I started to solve for this in our actions but thought I should post here first

[HarithaVattikuti]

Hello @jamesmehorter
Thank you for creating this issue. We will investigate it and get back to you as soon as we have some feedback.

[zzztimbo]

We are seeing a simliar issue as well.

[svrnm]

We see the same issue

Edit: another work around is restricting the activity types to opened and reopened and by that dropping synchronize, see here: "By default, a workflow only runs when a pull_request_target event's activity type is opened, synchronize, or reopened"