Confusing error when same volume name used twice

[bobcatfish]

Expected Behavior

If you try to use a volume name in a Task that is either already being used internally by Tekton (e.g. workspace) or you have already specified it yourself (resulting in a pod that is invalid), you should get an informative and helpful error.

Actual Behavior

Instead you get this cryptic error:

TaskRun volume-output-pipeline-run-then-check-and-write-wl4lv has failed (Missing or invalid Task default/files-exist-and-add-new: translating Build to Pod: expected exactly one, got both: name)

Steps to Reproduce the Problem

1. Create a Task and add a volume called workspace
2. Create a TaskRun that invokes the Task
3. Watch it fail and look at the error in the status

Additional Info

The error is coming from

pipeline/pkg/apis/pipeline/v1alpha1/task_validation.go

Line 107 in 7a0454b

func ValidateVolumes(volumes []corev1.Volume) *apis.FieldError {

which is being called by

pipeline/pkg/reconciler/taskrun/resources/pod.go

Line 300 in ef8a6b2

if err := v1alpha1.ValidateVolumes(volumes); err != nil {