Add the imageID for each step to the TaskRun.Spec.Status object.

This allows users to trace the exact steps (including digest) used in each TaskRun.
This information is already available on a Pod, but we need to assume completed Pods
will be GC'ed and not available long after the run is complete.

pkg/apis/pipeline/v1alpha1/taskrun_types.go

@@ -165,7 +165,8 @@ func (tr *TaskRunStatus) SetCondition(newCond *apis.Condition) {
 // StepState reports the results of running a step in the Task.
 type StepState struct {
  corev1.ContainerState
- Name string `json:"name,omitempty"`
+ Name string `json:"name,omitempty"`
+ ImageID string `json:"imageID,omitempty"`
 }
 
 // +genclient

pkg/status/taskrunpod.go

@@ -36,6 +36,7 @@ func UpdateStatusFromPod(taskRun *v1alpha1.TaskRun, pod *corev1.Pod, resourceLis
  taskRun.Status.Steps = append(taskRun.Status.Steps, v1alpha1.StepState{
  ContainerState: *s.State.DeepCopy(),
  Name: resources.TrimContainerNamePrefix(s.Name),
+ ImageID: s.ImageID,
  })
  }
  }

pkg/status/taskrunpod_test.go

@@ -74,7 +74,8 @@ func TestUpdateStatusFromPod(t *testing.T) {
  Terminated: &corev1.ContainerStateTerminated{
  ExitCode: 123,
  }},
- Name: "state-name",
+ Name: "state-name",
+ ImageID: "image-id",
  }},
  },
  }, {