bytes, strings: add ReplaceAll

Credit to Harald Nordgren for the proposal in
https://golang.org/cl/137456 and #27864.

Fixes #27864

Change-Id: I80546683b0623124fe4627a71af88add2f6c1c27
Reviewed-on: https://go-review.googlesource.com/137855Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/bytes/bytes.go

@@ -774,6 +774,15 @@ func Replace(s, old, new []byte, n int) []byte {
 	return t[0:w]
 }
 
+// ReplaceAll returns a copy of the slice s with all
+// non-overlapping instances of old replaced by new.
+// If old is empty, it matches at the beginning of the slice
+// and after each UTF-8 sequence, yielding up to k+1 replacements
+// for a k-rune slice.
+func ReplaceAll(s, old, new []byte) []byte {
+	return Replace(s, old, new, -1)
+}
+
 // EqualFold reports whether s and t, interpreted as UTF-8 strings,
 // are equal under Unicode case-folding.
 func EqualFold(s, t []byte) bool {

src/bytes/bytes_test.go

@@ -1362,6 +1362,12 @@ func TestReplace(t *testing.T) {
 		if cap(in) == cap(out) && &in[:1][0] == &out[:1][0] {
 			t.Errorf("Replace(%q, %q, %q, %d) didn't copy", tt.in, tt.old, tt.new, tt.n)
 		}
+		if tt.n == -1 {
+			out := ReplaceAll(in, []byte(tt.old), []byte(tt.new))
+			if s := string(out); s != tt.out {
+				t.Errorf("ReplaceAll(%q, %q, %q) = %q, want %q", tt.in, tt.old, tt.new, s, tt.out)
+			}
+		}
 	}
 }
 

src/strings/strings.go

@@ -874,6 +874,15 @@ func Replace(s, old, new string, n int) string {
 	return string(t[0:w])
 }
 
+// ReplaceAll returns a copy of the string s with all
+// non-overlapping instances of old replaced by new.
+// If old is empty, it matches at the beginning of the string
+// and after each UTF-8 sequence, yielding up to k+1 replacements
+// for a k-rune string.
+func ReplaceAll(s, old, new string) string {
+	return Replace(s, old, new, -1)
+}
+
 // EqualFold reports whether s and t, interpreted as UTF-8 strings,
 // are equal under Unicode case-folding.
 func EqualFold(s, t string) bool {

src/strings/strings_test.go

@@ -1243,6 +1243,12 @@ func TestReplace(t *testing.T) {
 		if s := Replace(tt.in, tt.old, tt.new, tt.n); s != tt.out {
 			t.Errorf("Replace(%q, %q, %q, %d) = %q, want %q", tt.in, tt.old, tt.new, tt.n, s, tt.out)
 		}
+		if tt.n == -1 {
+			s := ReplaceAll(tt.in, tt.old, tt.new)
+			if s != tt.out {
+				t.Errorf("ReplaceAll(%q, %q, %q) = %q, want %q", tt.in, tt.old, tt.new, s, tt.out)
+			}
+		}
 	}
 }