bytes,strings: add CutLast

Fixes #71151

Change-Id: I3b3d49c35b0fa2c1220d3f39bbd506cc072b52b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/764601
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/strings/strings.go b/src/strings/strings.go
index 367e0a8e24..70297f1e69 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -1289,3 +1289,14 @@ func CutPrefix(s, prefix string) (after string, found bool) {
 func CutSuffix(s, suffix string) (before string, found bool) {
 	return stringslite.CutSuffix(s, suffix)
 }
+
+// CutLast slices s around the last instance of sep,
+// returning the text before and after sep.
+// The found result reports whether sep appears in s.
+// If sep does not appear in s, CutLast returns s, "", false.
+func CutLast(s, sep string) (before, after string, found bool) {
+	if i := LastIndex(s, sep); i >= 0 {
+		return s[:i], s[i+len(sep):], true
+	}
+	return s, "", false
+}