Gitea not detecting merge conflict properly and failing to merge

[TheBrokenRail]

Description

I'm trying to merge a PR (with the method "Rebase then fast-forward"). But when I click the merge button, it just pops up a message saying "Network error." When I checked the logs it revealed it was an issue with merge conflicts.

The Gitea UI does say that the branch is out-of-date, but it says it should be OK to merge. The "Update branch by merge/rebase" button doesn't do anything and doesn't even appear on https://try.gitea.io.

The PR on https://try.gitea.io: https://try.gitea.io/TheBrokenRail/minecraft-pi-reborn/pulls/1

Gitea Version

v1.21.5

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

https://gist.github.com/TheBrokenRail/e6c0004d81c89d2d4af69688a4e01165

Screenshots

Git Version

2.40.1

Operating System

Ubuntu 22.04

How are you running Gitea?

Inside the official Docker container.

Database

SQLite

[yp05327]

Missing Redirect -> JSONRedirect changes in #28140

As we are using more and more form-fetch-action, maybe we need to add some tests for these responses.

[yp05327]

And these shouldn't be JSONError? IIRC, Flash will not work in this case.

[lunny]

This only affects v1.22, not v1.21.5 I'm wrong. It's backported.

[TheBrokenRail]

So from my understanding, this issue is really two issues?

1. Gitea isn't detecting the merge conflict correctly, and says it's ready to merge when it isn't.
2. When it does fails to merge, Gitea doesn't display the error correctly.

[Zettat123]

this issue is really two issues?

Yes. There are two issues.

1. The issue of error display. Caused by the bug mentioned in comment

2. As for the conflict detection failure, that's not a bug. Currently Gitea only detects conflicts with the "merge" method, not with the "rebase" method. I think Gitea should also detect conflicts with "rebase" and add some error messages to inform users that there are conflicts when using "rebase", like GitHub does.

[wxiaoguang]

wait for backport