nonGoOverlay map[string]string // map from non-.go source files to copied files in objdir. Nil if no overlay is used.
	traceSpan    *trace.Span
}

// BuildActionID returns the action ID section of a's build ID.
func (a *Action) BuildActionID() string { return actionID(a.buildID) }

// BuildContentID returns the content ID section of a's build ID.
func (a *Action) BuildContentID() string { return contentID(a.buildID) }