strings: add LastIndexAny

The need for a LastIndexAny function has come up in the discussion
for https://golang.org/cl/3008041/. This function is
implemented analogously to lastIndexFunc, using functions from
the utf8 package.

R=r, rsc, PeterGo
CC=golang-dev
https://golang.org/cl/3057041

src/pkg/bytes/bytes.go

@@ -165,6 +165,25 @@ func IndexAny(s []byte, chars string) int {
 	return -1
 }
 
+// LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code
+// points.  It returns the byte index of the last occurrence in s of any of
+// the Unicode code points in chars.  It returns -1 if chars is empty or if
+// there is no code point in common.
+func LastIndexAny(s []byte, chars string) int {
+	if len(chars) > 0 {
+		for i := len(s); i > 0; {
+			rune, size := utf8.DecodeLastRune(s[0:i])
+			i -= size
+			for _, m := range chars {
+				if rune == m {
+					return i
+				}
+			}
+		}
+	}
+	return -1
+}
+
 // Generic split: splits after each instance of sep,
 // including sepSave bytes of sep in the subarrays.
 func genSplit(s, sep []byte, sepSave, n int) [][]byte {

src/pkg/bytes/bytes_test.go

@@ -128,6 +128,20 @@ var indexAnyTests = []BinOpTest{
 	{dots + dots + dots, " ", -1},
 }
 
+var lastIndexAnyTests = []BinOpTest{
+	{"", "", -1},
+	{"", "a", -1},
+	{"", "abc", -1},
+	{"a", "", -1},
+	{"a", "a", 0},
+	{"aaa", "a", 2},
+	{"abc", "xyz", -1},
+	{"abc", "ab", 1},
+	{"a☺b☻c☹d", "uvw☻xyz", 2 + len("☺")},
+	{"a.RegExp*", ".(|)*+?^$[]", 8},
+	{dots + dots + dots, " ", -1},
+}
+
 var indexRuneTests = []BinOpTest{
 	{"", "a", -1},
 	{"", "☺", -1},
@@ -150,18 +164,23 @@ func runIndexTests(t *testing.T, f func(s, sep []byte) int, funcName string, tes
 	}
 }
 
-func TestIndex(t *testing.T)     { runIndexTests(t, Index, "Index", indexTests) }
-func TestLastIndex(t *testing.T) { runIndexTests(t, LastIndex, "LastIndex", lastIndexTests) }
-func TestIndexAny(t *testing.T) {
-	for _, test := range indexAnyTests {
+func runIndexAnyTests(t *testing.T, f func(s []byte, chars string) int, funcName string, testCases []BinOpTest) {
+	for _, test := range testCases {
 		a := []byte(test.a)
-		actual := IndexAny(a, test.b)
+		actual := f(a, test.b)
 		if actual != test.i {
-			t.Errorf("IndexAny(%q,%q) = %v; want %v", a, test.b, actual, test.i)
+			t.Errorf("%s(%q,%q) = %v; want %v", funcName, a, test.b, actual, test.i)
 		}
 	}
 }
 
+func TestIndex(t *testing.T)     { runIndexTests(t, Index, "Index", indexTests) }
+func TestLastIndex(t *testing.T) { runIndexTests(t, LastIndex, "LastIndex", lastIndexTests) }
+func TestIndexAny(t *testing.T)  { runIndexAnyTests(t, IndexAny, "IndexAny", indexAnyTests) }
+func TestLastIndexAny(t *testing.T) {
+	runIndexAnyTests(t, LastIndexAny, "LastIndexAny", lastIndexAnyTests)
+}
+
 func TestIndexByte(t *testing.T) {
 	for _, tt := range indexTests {
 		if len(tt.b) != 1 {

src/pkg/strings/strings.go

@@ -142,6 +142,24 @@ func IndexAny(s, chars string) int {
 	return -1
 }
 
+// LastIndexAny returns the index of the last instance of any Unicode code
+// point from chars in s, or -1 if no Unicode code point from chars is
+// present in s.
+func LastIndexAny(s, chars string) int {
+	if len(chars) > 0 {
+		for i := len(s); i > 0; {
+			rune, size := utf8.DecodeLastRuneInString(s[0:i])
+			i -= size
+			for _, m := range chars {
+				if rune == m {
+					return i
+				}
+			}
+		}
+	}
+	return -1
+}
+
 // Generic split: splits after each instance of sep,
 // including sepSave bytes of sep in the subarrays.
 func genSplit(s, sep string, sepSave, n int) []string {

src/pkg/strings/strings_test.go

@@ -86,6 +86,19 @@ var indexAnyTests = []IndexTest{
 	{"aRegExp*", ".(|)*+?^$[]", 7},
 	{dots + dots + dots, " ", -1},
 }
+var lastIndexAnyTests = []IndexTest{
+	{"", "", -1},
+	{"", "a", -1},
+	{"", "abc", -1},
+	{"a", "", -1},
+	{"a", "a", 0},
+	{"aaa", "a", 2},
+	{"abc", "xyz", -1},
+	{"abc", "ab", 1},
+	{"a☺b☻c☹d", "uvw☻xyz", 2 + len("☺")},
+	{"a.RegExp*", ".(|)*+?^$[]", 8},
+	{dots + dots + dots, " ", -1},
+}
 
 // Execute f on each test case.  funcName should be the name of f; it's used
 // in failure reports.
@@ -101,6 +114,7 @@ func runIndexTests(t *testing.T, f func(s, sep string) int, funcName string, tes
 func TestIndex(t *testing.T)        { runIndexTests(t, Index, "Index", indexTests) }
 func TestLastIndex(t *testing.T)    { runIndexTests(t, LastIndex, "LastIndex", lastIndexTests) }
 func TestIndexAny(t *testing.T)     { runIndexTests(t, IndexAny, "IndexAny", indexAnyTests) }
+func TestLastIndexAny(t *testing.T) { runIndexTests(t, LastIndexAny, "LastIndexAny", lastIndexAnyTests) }
 
 type ExplodeTest struct {
 	s string