Branch not checked out in prebuild

[nVitius]

Bug description

I'm running into an issue where starting a prebuild with the "New Workspace (with this prebuild)" button is not checking out the branch. Looking at the code, this is intentional:

gitpod/components/server/ee/src/workspace/workspace-factory.ts

Lines 375 to 385 in 4c6b224

	if (OpenPrebuildContext.is(context.originalContext)) {
	// Because of incremental prebuilds, createForContext will take over the original context.
	// To ensure we get the right commit when forcing a prebuild, we force the context here.
	context.originalContext = buildWorkspace.context;
	if (CommitContext.is(context.originalContext)) {
	// We force the checkout of the revision rather than the ref/branch.
	// Otherwise we'd the correct prebuild with the "wrong" Git status.
	delete context.originalContext.ref;
	}
	}

This makes sense, except that I'm using the prebuild for the latest commit on this branch. Would it be possible to checkout the branch in this case?

Steps to reproduce

• Push new commit to branch w/ prebuilds enabled
• Navigate to Prebuilds tab in the project
• Select latest prebuild and start a new workspace

Workspace affected

No response

Expected behavior

Opening a prebuild for the latest commit on a branch should checkout the branch.

Example repository

No response

Anything else?

No response

[nVitius]

This is probably a separate issue but:

Clicking on the New Workspace button here for a branch that has a prebuild ready is ignoring the prebuild for me. I think it is happening for this non-default branch whenever it is not the most-recently updated branch. Making a commit on that branch and running the workspace right after the prebuild finishes and no other branches have been pushed to seems to work correctly.

[axonasif]

Duplicate of #13991

Probably

[nVitius]

@axonasif I don't think it's the same. That issue mentions the wrong branch being checked out.
This one is specifically related to the block of code I linked to (added recently in #13768 btw). It only applies to workspaces started with the new open-prebuild/<prebuild-id> context url.

You can see that the ref is being removed. This results in the correct commit being checked out, but Git being in a detached state. Here's an example:

I created a workspace using the latest prebuild for a branch. You can see that the branch commit and the checked out commit are the same, but we are not in the branch.

[geropl]

@axonasif I don't think it's the same. That issue mentions the wrong branch being checked out.

@nVitius I think you're right. It's just that we're not using that feature yet as it's so new. Even more impressive that you managed to come up with a PR to fix it! 👍 I'll ask my colleagues if someone can help review it. 💯

[jankeromnes]

Awesome find, and even more awesome contribution 💯 thanks! I can take a look at the PR. 👀

[jankeromnes]

Also, it's easy to reproduce this issue (so we know for sure that it has nothing to do with the aforementioned potential PVC/Prebuild bug):

I guess this will be an opportunity to better understand the "context fixing" code mentioned in the issue. 🔍

[jankeromnes]

Taking a look at my affected workspace in the DB:

• Workspace ID: jankeromnes-gitpodstagi-7hb8zw0g5wc

• Context URL: open-prebuild/699b3aa8-bb32-405c-9f5b-eda4bb27861d/https://github.com/jankeromnes/gitpod-staging-prebuilds/tree/master

• Parsed context:

{
  "refType": "branch",
  "isFile": false,
  "path": "",
  "title": "jankeromnes/gitpod-staging-prebuilds - master",
  "revision": "fd9fa6f1c215e51d0e5ddab962fd8f2d73c568a3",
  "repository": {
    "cloneUrl": "https://github.com/jankeromnes/gitpod-staging-prebuilds.git",
    "host": "github.com",
    "name": "gitpod-staging-prebuilds",
    "owner": "jankeromnes",
    "private": false
  },
  "normalizedContextURL": "https://github.com/jankeromnes/gitpod-staging-prebuilds/tree/master",
  "checkoutLocation": "gitpod-staging-prebuilds",
  "snapshotBucketId": "workspaces/jankeromnes-gitpodstagi-zr6eharwmsx/snapshot-1666336408404537268.tar@gitpod-prod-user-643ac637-74ae-4f82-9a86-c8527eb1e496",
  "prebuildWorkspaceId": "699b3aa8-bb32-405c-9f5b-eda4bb27861d",
  "wasPrebuilt": true
}

If we compare this with just opening https://github.com/jankeromnes/gitpod-staging-prebuilds/tree/master in Gitpod, which does check out the correct branch, we notice that the only difference in the parsed context is this extra field (which is absent above):

{
  "ref": "master",
  ...
}

[nVitius]

Thanks for the comments, guys. Happy to help get this resolved.

If we compare this with just opening https://github.com/jankeromnes/gitpod-staging-prebuilds/tree/master in Gitpod, which does check out the correct branch, we notice that the only difference in the parsed context is this extra field (which is absent above):

The code block I linked to in the OP is responsible for doing this. Any workspaces opened with the open-prebuild prefix are assumed to be ones were a specific prebuild was selected. If the prebuild is perhaps older, we want to make sure that the commit used at the time it was generated is also the one checked out (otherwise your prebuild might not be valid anymore). Thus, the ref is removed (now the branch is not checked out but the commit hash directly) and the originalContext is replaced with the one that the prebuild had (this is buildWorkspace.context).

This all makes sense for prebuilds where the commit is not also the latest one in the branch (context.ref). The code I added in the PR checks the content.originalContext and buildWorkspace.context (the one from the prebuild) to see if they resolve to the same commit hash. If they do, then we skip the step where the ref is removed and the context replaced.