Wrong usage of Gitea API for fetching head branch name

[proton-ab]

What Renovate type are you using?
Self-hosted, Gitea.

Describe the bug
Renovate looks up at ref in order to fetch the name of head branch for Gitea PR, however that field will point to unnamed reference when branch is removed.

Did you see anything helpful in debug logs?
No

To Reproduce
Using Gitea 1.12 as of commit 3d7d828a35dc187ae56c62fc438715d3dee78f3f

• Create basic repository and set it up
• Have Renovate run on it and create PR
• Close the PR
• Renovate will see closed PR and remove the branch
• On next run, Renovate can no longer identify PR that was closed and create new one

Additional context
Gitea added ability for deleted branches names to be retained in go-gitea/gitea#10413, this issue affects only Gitea versions >= 1.12.

Gitea API exposes two fields of interest for Renovate for head branch on PR - ref and label. Usually when PR is open and branch exist, both of them contain same information - branch name. When PR is closed and branch removed, label still contains the correct branch name, while ref points at unnamed reference within Git repository.

I have opened PR to fix this in #5998, this issue is for tracking purposes only.

[proton-ab]

Further documentation is here: https://github.com/go-gitea/gitea/blob/bb4261a5ed678235fadef279fe1ba1505993a406/templates/swagger/v1_json.tmpl#L12804

The tests on Gitea side can be seen here https://github.com/go-gitea/gitea/blob/5abe1c52de533b52725b1e584db9fea6fb1b39ab/modules/convert/pull_test.go#L25

As well as actual implementation here: https://github.com/go-gitea/gitea/blob/3fc4f3670cb748e02d786111d2029ef1e23a9640/modules/convert/pull.go#L72 (for existing branches, Ref is reset to name on line 130 https://github.com/go-gitea/gitea/blob/3fc4f3670cb748e02d786111d2029ef1e23a9640/modules/convert/pull.go#L130)

[rarkins]

@proton-ab thanks for the fix!

[renovate-release]

🎉 This issue has been resolved in version 19.216.3 🎉

The release is available on:

• GitHub release
• 19.216.3

Your semantic-release bot 📦🚀