webhookCommit will be updated by the old one

[1242504179-source]

WebhookCommit is obtained through webhooks. If the order of two webhooks is incorrect, how can we ensure that the new webhookCommit will not be updated by the old one?

[weyfonk]

This could be tricky, as commit histories may not be linear, meaning that saving timestamps of commits alone would not help Fleet's webhook server determine if one commit was created before another one: instead, the server would need to be aware of the order of commits, or at least the order of pushes.

Depending on providers, this may be achievable by looking at before/after-push SHAs, e.g. before/after for Gitlab, Github or Gogs, push.old/push.new for Bitbucket. Not sure if Azure DevOps' resource.refUpdates.{old,new}ObjectId would convey the same meaning though.

Then, if the server receives a push event which after field matches the before field of a recently received, and already processed event, it could discard that event. But that would involve some kind of additional state on the GitRepo.
And further questions would arise, such as:

• should any event which after matches an already received before be discarded? What if its before does not match any known state? Should the event be queued, in the hope that another event would then be received, enabling the server to reconstitute the original order of pushes?
• to enable this kind of logic to run, how many references should be stored?