Incremental Prebuilds can sometimes execute an outdated config

[jankeromnes]

Bug description

When Incremental Prebuilds are enabled for a project, new prebuilds will look for a compatible parent prebuild (by looking up the ancestor commits) in order to use it as a base and make the new prebuild faster.

"Compatible" means, among other things, that both the parent and the new prebuild have the exact same set of init, before and prebuild tasks.

If a compatible parent prebuild is found, the new prebuild is started from the older prebuild, and simply runs the init tasks again:

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

Line 111 in 91c09f7

ws = await this.createForPrebuiltWorkspace({span}, user, incrementalPrebuildContext, normalizedContextURL);

However, the effective configuration of the new incremental prebuild is copied over from the (parent) prebuild:

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

Line 204 in 91c09f7

const config = { ... buildWorkspace.config };

This works well for before, prebuild and init tasks (because we check that they are identical when looking for a compatible parent), however, if the command tasks (or anything else in the config) has changed since the parent prebuild was created, the new incremental prebuild will get an outdated config and GITPOD_TASKS, and e.g. execute oudated command tasks on startup (even if the .gitpod.yml in the repo shows the newer tasks).

This happened to @mads-hartmann in #7456

Steps to reproduce

1. Run a full Prebuild for a repository with both an init task and a command task, then wait for it to be successful
2. Enable Incremental Prebuilds for that repository
3. Push a new commit to the same branch as in 1. that modifies the command task, and wait for this new commit to prebuild successfully
4. Open a workspace based on the new, incremental prebuild

Expected:

• The new command task should be run

Observed:

• The old command task is executed (or, if the .gitpod.yml did not have a command in 1., no command task is executed at all)

Workspace affected

No response

Expected behavior

No response

Example repository

No response

Anything else?

No response