strings, bytes: add CutPrefix and CutSuffix

Fixes #42537

Change-Id: Ie03c2614ffee30ebe707acad6b9f6c28fb134a45
Reviewed-on: https://go-review.googlesource.com/c/go/+/407176
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Changkun Ou <mail@changkun.de>
Reviewed-by: Ian Lance Taylor <iant@google.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
index a1604c2c47..d6153aa226 100644
--- a/src/strings/strings_test.go
+++ b/src/strings/strings_test.go
@@ -1611,6 +1611,48 @@ func TestCut(t *testing.T) {
 	}
 }
 
+var cutPrefixTests = []struct {
+	s, sep string
+	after  string
+	found  bool
+}{
+	{"abc", "a", "bc", true},
+	{"abc", "abc", "", true},
+	{"abc", "", "abc", true},
+	{"abc", "d", "abc", false},
+	{"", "d", "", false},
+	{"", "", "", true},
+}
+
+func TestCutPrefix(t *testing.T) {
+	for _, tt := range cutPrefixTests {
+		if after, found := CutPrefix(tt.s, tt.sep); after != tt.after || found != tt.found {
+			t.Errorf("CutPrefix(%q, %q) = %q, %v, want %q, %v", tt.s, tt.sep, after, found, tt.after, tt.found)
+		}
+	}
+}
+
+var cutSuffixTests = []struct {
+	s, sep string
+	after  string
+	found  bool
+}{
+	{"abc", "bc", "a", true},
+	{"abc", "abc", "", true},
+	{"abc", "", "abc", true},
+	{"abc", "d", "abc", false},
+	{"", "d", "", false},
+	{"", "", "", true},
+}
+
+func TestCutSuffix(t *testing.T) {
+	for _, tt := range cutSuffixTests {
+		if after, found := CutSuffix(tt.s, tt.sep); after != tt.after || found != tt.found {
+			t.Errorf("CutSuffix(%q, %q) = %q, %v, want %q, %v", tt.s, tt.sep, after, found, tt.after, tt.found)
+		}
+	}
+}
+
 func makeBenchInputHard() string {
 	tokens := [...]string{
 		"<a>", "<p>", "<b>", "<strong>",