for _, p := range policiesToUpdate.ToSlice() {
			if _, found := cache.iamPolicyDocsMap[p]; !found {
				err = errNoSuchPolicy
				return
			}
		}
		newPolicySet = existingPolicySet.Union(policiesToUpdate)
	} else {
		// policies to detach => inputPolicies ∩ existing (intersection)
		policiesToUpdate = policiesToUpdate.Intersection(existingPolicySet)

// struct_foo becomes "struct foo", and similarly for
// union and enum.
func cname(s string) string {
	if t, ok := nameToC[s]; ok {
		return t
	}

	if strings.HasPrefix(s, "struct_") {
		return "struct " + s[len("struct_"):]
	}
	if strings.HasPrefix(s, "union_") {
		return "union " + s[len("union_"):]
	}
	if strings.HasPrefix(s, "enum_") {
		return "enum " + s[len("enum_"):]
	}