Support "^" character is compare API to designate previous commits

[ybizeul]

Feature Description

GitHub API lets you compare commits with a special trick to target the previous commit by using the ^ character, it is described here : https://docs.github.com/en/pull-requests/committing-changes-to-your-project/viewing-and-comparing-commits/comparing-commits#comparisons-across-commits

When using this syntax, Gitea returns :

{"errors":null,"message":"The target couldn't be found.","url":"https://gitea.mydomain.com/api/swagger"}

Because of that, things like https://github.com/marketplace/actions/release-changelog-builder don't work, and their specific support for gitea repositories is broken so it's totally unusable.

Screenshots

No response

[lunny]

#32786 should resolve this problem

[ybizeul]

Any hope that it’ll be merged ?

[lunny]

After #36105, the work should be easier than before.

[eyupcanakman]

@lunny now that #36105 landed I'd like to pick this up. Plan: resolve <ref><suffix> to a commit via ConvertToGitID (it handles ^ and ~N), then drop the suffix guard in the API and web compare paths.

A few things before I open a PR:

• I think base...head^ should work too, so I'd add HeadOriRefSuffix and parse the suffix on the head side. Sound right?
• ~N too, or just ^ for now?
• OK to leave the DirectComparison ^ FIXME for a separate PR?

[lunny]

@lunny now that #36105 landed I'd like to pick this up. Plan: resolve <ref><suffix> to a commit via ConvertToGitID (it handles ^ and ~N), then drop the suffix guard in the API and web compare paths.

A few things before I open a PR:

• I think base...head^ should work too, so I'd add HeadOriRefSuffix and parse the suffix on the head side. Sound right?

I think yes.

• ~N too, or just ^ for now?

It's better to have ~N but ParseRefSuffix need some updates.

• OK to leave the DirectComparison ^ FIXME for a separate PR?

What's the different DirectComparison and non-DirectComparison when handling ^?