--- /dev/null
+// Copyright 2018, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cmpopts
+
+import (
+ "github.com/google/go-cmp/cmp"
+)
+
+type xformFilter struct{ xform cmp.Option }
+
+func (xf xformFilter) filter(p cmp.Path) bool {
+ for _, ps := range p {
+ if t, ok := ps.(cmp.Transform); ok && t.Option() == xf.xform {
+ return false
+ }
+ }
+ return true
+}
+
+// AcyclicTransformer returns a Transformer with a filter applied that ensures
+// that the transformer cannot be recursively applied upon its own output.
+//
+// An example use case is a transformer that splits a string by lines:
+// AcyclicTransformer("SplitLines", func(s string) []string{
+// return strings.Split(s, "\n")
+// })
+//
+// Had this been an unfiltered Transformer instead, this would result in an
+// infinite cycle converting a string to []string to [][]string and so on.
+func AcyclicTransformer(name string, xformFunc interface{}) cmp.Option {
+ xf := xformFilter{cmp.Transformer(name, xformFunc)}
+ return cmp.FilterPath(xf.filter, xf.xform)
+}