Add IndexFunc and LastIndexFunc.

Change TrimRight and TrimLeft to use these functions.
Incidentally fix minor bug in TrimRight.
Add some test cases for this.
YMMV whether it's worth saving the closure allocation.

R=r, r2
CC=golang-dev, hoisie, rsc
https://golang.org/cl/1198044

src/pkg/strings/strings_test.go

@@ -283,8 +283,14 @@ var trimSpaceTests = []StringTest{
 	StringTest{" \t\r\n x\t\t\r\r\n\n ", "x"},
 	StringTest{" \u2000\t\r\n x\t\t\r\r\ny\n \u3000", "x\t\t\r\r\ny"},
 	StringTest{"1 \t\r\n2", "1 \t\r\n2"},
-	StringTest{" x\x80", "x\x80"}, // invalid UTF-8 on end
-	StringTest{" x\xc0", "x\xc0"}, // invalid UTF-8 on end
+	StringTest{" x\x80", "x\x80"},
+	StringTest{" x\xc0", "x\xc0"},
+	StringTest{"x \xc0\xc0 ", "x \xc0\xc0"},
+	StringTest{"x \xc0", "x \xc0"},
+	StringTest{"x \xc0 ", "x \xc0"},
+	StringTest{"x \xc0\xc0 ", "x \xc0\xc0"},
+	StringTest{"x ☺\xc0\xc0 ", "x ☺\xc0\xc0"},
+	StringTest{"x ☺ ", "x ☺"},
 }
 
 func tenRunes(rune int) string {
@@ -407,8 +413,28 @@ var trimTests = []TrimTest{
 	TrimTest{TrimRight, "abba", "", "abba"},
 	TrimTest{TrimRight, "", "123", ""},
 	TrimTest{TrimRight, "", "", ""},
+	TrimTest{TrimRight, "☺\xc0", "☺", "☺\xc0"},
 }
 
+// naiveTrimRight implements a version of TrimRight
+// by scanning forwards from the start of s.
+func naiveTrimRight(s string, cutset string) string {
+	i := -1
+	for j, r := range s {
+		if IndexRune(cutset, r) == -1 {
+			i = j
+		}
+	}
+	if i >= 0 && s[i] >= utf8.RuneSelf {
+		_, wid := utf8.DecodeRuneInString(s[i:])
+		i += wid
+	} else {
+		i++
+	}
+	return s[0:i]
+}
+
+
 func TestTrim(t *testing.T) {
 	for _, tc := range trimTests {
 		actual := tc.f(tc.in, tc.cutset)
@@ -426,25 +452,100 @@ func TestTrim(t *testing.T) {
 		if actual != tc.out {
 			t.Errorf("%s(%q, %q) = %q; want %q", name, tc.in, tc.cutset, actual, tc.out)
 		}
+		// test equivalence of TrimRight to naive version
+		if tc.f == TrimRight {
+			naive := naiveTrimRight(tc.in, tc.cutset)
+			if naive != actual {
+				t.Errorf("TrimRight(%q, %q) = %q, want %q", tc.in, tc.cutset, actual, naive)
+			}
+		}
 	}
 }
 
+var isSpace = predicate{unicode.IsSpace, "IsSpace"}
+var isDigit = predicate{unicode.IsDigit, "IsDigit"}
+var isUpper = predicate{unicode.IsUpper, "IsUpper"}
+var isValidRune = predicate{
+	func(r int) bool {
+		return r != utf8.RuneError
+	},
+	"IsValidRune",
+}
+
+type predicate struct {
+	f    func(r int) bool
+	name string
+}
+
 type TrimFuncTest struct {
-	f             func(r int) bool
-	name, in, out string
+	f       predicate
+	in, out string
+}
+
+func not(p predicate) predicate {
+	return predicate{
+		func(r int) bool {
+			return !p.f(r)
+		},
+		"not " + p.name,
+	}
 }
 
 var trimFuncTests = []TrimFuncTest{
-	TrimFuncTest{unicode.IsSpace, "IsSpace", space + " hello " + space, "hello"},
-	TrimFuncTest{unicode.IsDigit, "IsDigit", "\u0e50\u0e5212hello34\u0e50\u0e51", "hello"},
-	TrimFuncTest{unicode.IsUpper, "IsUpper", "\u2C6F\u2C6F\u2C6F\u2C6FABCDhelloEF\u2C6F\u2C6FGH\u2C6F\u2C6F", "hello"},
+	TrimFuncTest{isSpace, space + " hello " + space, "hello"},
+	TrimFuncTest{isDigit, "\u0e50\u0e5212hello34\u0e50\u0e51", "hello"},
+	TrimFuncTest{isUpper, "\u2C6F\u2C6F\u2C6F\u2C6FABCDhelloEF\u2C6F\u2C6FGH\u2C6F\u2C6F", "hello"},
+	TrimFuncTest{not(isSpace), "hello" + space + "hello", space},
+	TrimFuncTest{not(isDigit), "hello\u0e50\u0e521234\u0e50\u0e51helo", "\u0e50\u0e521234\u0e50\u0e51"},
+	TrimFuncTest{isValidRune, "ab\xc0a\xc0cd", "\xc0a\xc0"},
+	TrimFuncTest{not(isValidRune), "\xc0a\xc0", "a"},
 }
 
 func TestTrimFunc(t *testing.T) {
 	for _, tc := range trimFuncTests {
-		actual := TrimFunc(tc.in, tc.f)
+		actual := TrimFunc(tc.in, tc.f.f)
 		if actual != tc.out {
-			t.Errorf("TrimFunc(%q, %q) = %q; want %q", tc.in, tc.name, actual, tc.out)
+			t.Errorf("TrimFunc(%q, %q) = %q; want %q", tc.in, tc.f.name, actual, tc.out)
+		}
+	}
+}
+
+type IndexFuncTest struct {
+	in          string
+	f           predicate
+	first, last int
+}
+
+var indexFuncTests = []IndexFuncTest{
+	IndexFuncTest{"", isValidRune, -1, -1},
+	IndexFuncTest{"abc", isDigit, -1, -1},
+	IndexFuncTest{"0123", isDigit, 0, 3},
+	IndexFuncTest{"a1b", isDigit, 1, 1},
+	IndexFuncTest{space, isSpace, 0, len(space) - 3}, // last rune in space is 3 bytes
+	IndexFuncTest{"\u0e50\u0e5212hello34\u0e50\u0e51", isDigit, 0, 18},
+	IndexFuncTest{"\u2C6F\u2C6F\u2C6F\u2C6FABCDhelloEF\u2C6F\u2C6FGH\u2C6F\u2C6F", isUpper, 0, 34},
+	IndexFuncTest{"12\u0e50\u0e52hello34\u0e50\u0e51", not(isDigit), 8, 12},
+
+	// broken unicode tests
+	IndexFuncTest{"\x801", isDigit, 1, 1},
+	IndexFuncTest{"\x80abc", isDigit, -1, -1},
+	IndexFuncTest{"\xc0a\xc0", isValidRune, 1, 1},
+	IndexFuncTest{"\xc0a\xc0", not(isValidRune), 0, 2},
+	IndexFuncTest{"\xc0☺\xc0", not(isValidRune), 0, 4},
+	IndexFuncTest{"\xc0☺\xc0\xc0", not(isValidRune), 0, 5},
+	IndexFuncTest{"ab\xc0a\xc0cd", not(isValidRune), 2, 4},
+	IndexFuncTest{"a\xe0\x80cd", not(isValidRune), 1, 2},
+}
+
+func TestIndexFunc(t *testing.T) {
+	for _, tc := range indexFuncTests {
+		first := IndexFunc(tc.in, tc.f.f)
+		if first != tc.first {
+			t.Errorf("IndexFunc(%q, %s) = %d; want %d", tc.in, tc.f.name, first, tc.first)
+		}
+		last := LastIndexFunc(tc.in, tc.f.f)
+		if last != tc.last {
+			t.Errorf("LastIndexFunc(%q, %s) = %d; want %d", tc.in, tc.f.name, last, tc.last)
 		}
 	}
 }