Description

An open pull request is shown as "outdated" after a tag is added to (or at) the destination branch, even though nothing on the source branch has changed and the source branch is still up to date.

Steps to reproduce

1. Open a pull request with source branch A and destination branch B.
2. Confirm the pull request is not outdated.
3. Create a tag on/at the destination branch B.
4. Refresh the pull request page.

Expected

The pull request should not be reported as outdated — the source branch was not modified and no conflicting change was made to the destination branch.

Actual

The pull request is reported as outdated, because the cached merge preview is invalidated by the tag ref update and has to be recalculated against the destination branch revision.

Notes

• The "outdated" notice relates to the cached merge preview (trial merge of source into the current tip of the destination branch), not to the source branch commits.
• Creating a tag is a ref update on the project, which appears to be treated the same as a branch tip change for the purposes of invalidating the merge preview. It would be preferable to only invalidate the preview when the destination branch tip actually changes.

Affected Versions: v16.9.5