GCB builder incorrectly assumes GCP project from supplied WorkerPool property for Cloud Build execution

[bogdannazarenko]

Bug:
Given the following GoogleCloudBuild configuration:

- name: cloud-build
    build:
      googleCloudBuild:
        projectId: projectA
        region: us-east1
        workerPool: projects/projectB/locations/us-central1/workerPools/my-private-pool
        serviceAccount: projects/projectA/serviceAccounts/my-service-account@projectA.iam.gserviceaccount.com

current region definition:

configures the region to run the build. If WorkerPool is configured, the region will be deduced from the WorkerPool configuration. If neither WorkerPool nor Region is configured, the build will be run in global(non-regional). See Cloud Build locations.

When WorkerPool property is supplied to GoogleCloudBuild configuration, gcb Builder incorrectly assumes the destination project for Cloud Build is project from WorkerPool string. The gcb Builder needs to create build in projectA but it erroneously fetches the location as projects/projectB/locations/us-east1 and tries to create a build in projectB.

This is not how Cloud Build Worker Pool configuration is suppose to work. The Cloud Build execution should be in projectA which is then using a shared/private Cloud Build Private Pool from a different project (projectB). Common pattern in enterprise environments.

Solution:
Update code that fetches location from WorkerPool string to use supplied projectID instead of assuming project from WorkerPool string.