all: omit unnecessary 0 in slice expression

All changes are related to the code, except for the comments in src/regexp/syntax/parse.go and src/slices/slices.go.

Change-Id: I73c5d3c54099749b62210aa7f3182c5eb84bb6a6
GitHub-Last-Rev: 794aa9b053
GitHub-Pull-Request: golang/go#69170
Reviewed-on: https://go-review.googlesource.com/c/go/+/609678
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/bufio/bufio_test.go

@@ -636,7 +636,7 @@ func TestWriter(t *testing.T) {
 			for l := 0; l < len(written); l++ {
 				if written[l] != data[l] {
 					t.Errorf("wrong bytes written")
-					t.Errorf("want=%q", data[0:len(written)])
+					t.Errorf("want=%q", data[:len(written)])
 					t.Errorf("have=%q", written)
 				}
 			}

src/bytes/buffer_test.go

@@ -213,7 +213,7 @@ func TestLargeByteWrites(t *testing.T) {
 func TestLargeStringReads(t *testing.T) {
 	var buf Buffer
 	for i := 3; i < 30; i += 3 {
-		s := fillString(t, "TestLargeReads (1)", &buf, "", 5, testString[0:len(testString)/i])
+		s := fillString(t, "TestLargeReads (1)", &buf, "", 5, testString[:len(testString)/i])
 		empty(t, "TestLargeReads (2)", &buf, s, make([]byte, len(testString)))
 	}
 	check(t, "TestLargeStringReads (3)", &buf, "")
@@ -222,7 +222,7 @@ func TestLargeStringReads(t *testing.T) {
 func TestLargeByteReads(t *testing.T) {
 	var buf Buffer
 	for i := 3; i < 30; i += 3 {
-		s := fillBytes(t, "TestLargeReads (1)", &buf, "", 5, testBytes[0:len(testBytes)/i])
+		s := fillBytes(t, "TestLargeReads (1)", &buf, "", 5, testBytes[:len(testBytes)/i])
 		empty(t, "TestLargeReads (2)", &buf, s, make([]byte, len(testString)))
 	}
 	check(t, "TestLargeByteReads (3)", &buf, "")
@@ -274,7 +274,7 @@ func TestNil(t *testing.T) {
 func TestReadFrom(t *testing.T) {
 	var buf Buffer
 	for i := 3; i < 30; i += 3 {
-		s := fillBytes(t, "TestReadFrom (1)", &buf, "", 5, testBytes[0:len(testBytes)/i])
+		s := fillBytes(t, "TestReadFrom (1)", &buf, "", 5, testBytes[:len(testBytes)/i])
 		var b Buffer
 		b.ReadFrom(&buf)
 		empty(t, "TestReadFrom (2)", &b, s, make([]byte, len(testString)))
@@ -337,7 +337,7 @@ func TestReadFromNegativeReader(t *testing.T) {
 func TestWriteTo(t *testing.T) {
 	var buf Buffer
 	for i := 3; i < 30; i += 3 {
-		s := fillBytes(t, "TestWriteTo (1)", &buf, "", 5, testBytes[0:len(testBytes)/i])
+		s := fillBytes(t, "TestWriteTo (1)", &buf, "", 5, testBytes[:len(testBytes)/i])
 		var b Buffer
 		buf.WriteTo(&b)
 		empty(t, "TestWriteTo (2)", &b, s, make([]byte, len(testString)))

src/bytes/bytes.go

@@ -592,7 +592,7 @@ func Join(s [][]byte, sep []byte) []byte {
 
 // HasPrefix reports whether the byte slice s begins with prefix.
 func HasPrefix(s, prefix []byte) bool {
-	return len(s) >= len(prefix) && Equal(s[0:len(prefix)], prefix)
+	return len(s) >= len(prefix) && Equal(s[:len(prefix)], prefix)
 }
 
 // HasSuffix reports whether the byte slice s ends with suffix.

src/cmd/internal/notsha256/sha256_test.go

@@ -86,7 +86,7 @@ func TestGolden(t *testing.T) {
 			if j < 2 {
 				io.WriteString(c, g.in)
 			} else {
-				io.WriteString(c, g.in[0:len(g.in)/2])
+				io.WriteString(c, g.in[:len(g.in)/2])
 				c.Sum(nil)
 				io.WriteString(c, g.in[len(g.in)/2:])
 			}

src/crypto/cipher/ctr_aes_test.go

@@ -80,7 +80,7 @@ func TestCTR_AES(t *testing.T) {
 			ctr := cipher.NewCTR(c, tt.iv)
 			encrypted := make([]byte, len(in))
 			ctr.XORKeyStream(encrypted, in)
-			if out := tt.out[0:len(in)]; !bytes.Equal(out, encrypted) {
+			if out := tt.out[:len(in)]; !bytes.Equal(out, encrypted) {
 				t.Errorf("%s/%d: CTR\ninpt %x\nhave %x\nwant %x", test, len(in), in, encrypted, out)
 			}
 		}
@@ -90,7 +90,7 @@ func TestCTR_AES(t *testing.T) {
 			ctr := cipher.NewCTR(c, tt.iv)
 			plain := make([]byte, len(in))
 			ctr.XORKeyStream(plain, in)
-			if out := tt.in[0:len(in)]; !bytes.Equal(out, plain) {
+			if out := tt.in[:len(in)]; !bytes.Equal(out, plain) {
 				t.Errorf("%s/%d: CTRReader\nhave %x\nwant %x", test, len(out), plain, out)
 			}
 		}

src/crypto/internal/cryptotest/aead.go

@@ -204,8 +204,8 @@ func TestAEAD(t *testing.T, mAEAD MakeAEAD) {
 							out := sealMsg(t, aead, prefix, nonce, plaintext, addData)
 
 							// Check that Seal didn't alter the prefix
-							if !bytes.Equal(out[0:len(prefix)], prefix) {
-								t.Errorf("Seal alters dst instead of appending; got %s, want %s", truncateHex(out[0:len(prefix)]), truncateHex(prefix))
+							if !bytes.Equal(out[:len(prefix)], prefix) {
+								t.Errorf("Seal alters dst instead of appending; got %s, want %s", truncateHex(out[:len(prefix)]), truncateHex(prefix))
 							}
 
 							ciphertext := out[len(prefix):]
@@ -237,8 +237,8 @@ func TestAEAD(t *testing.T, mAEAD MakeAEAD) {
 							out := openWithoutError(t, aead, prefix, nonce, ciphertext, addData)
 
 							// Check that Open didn't alter the prefix
-							if !bytes.Equal(out[0:len(prefix)], prefix) {
-								t.Errorf("Open alters dst instead of appending; got %s, want %s", truncateHex(out[0:len(prefix)]), truncateHex(prefix))
+							if !bytes.Equal(out[:len(prefix)], prefix) {
+								t.Errorf("Open alters dst instead of appending; got %s, want %s", truncateHex(out[:len(prefix)]), truncateHex(prefix))
 							}
 
 							after := out[len(prefix):]

src/crypto/internal/cryptotest/hash.go

@@ -39,8 +39,8 @@ func TestHash(t *testing.T, mh MakeHash) {
 			sum := getSum(t, h, prefix) // Append new digest to prefix
 
 			// Check that Sum didn't alter the prefix
-			if !bytes.Equal(sum[0:len(prefix)], prefix) {
-				t.Errorf("Sum alters passed buffer instead of appending; got %x, want %x", sum[0:len(prefix)], prefix)
+			if !bytes.Equal(sum[:len(prefix)], prefix) {
+				t.Errorf("Sum alters passed buffer instead of appending; got %x, want %x", sum[:len(prefix)], prefix)
 			}
 
 			// Check that the appended sum wasn't affected by the prefix

src/crypto/md5/md5_test.go

@@ -69,7 +69,7 @@ func TestGolden(t *testing.T) {
 			if j < 2 {
 				io.WriteString(c, g.in)
 			} else if j == 2 {
-				io.WriteString(c, g.in[0:len(g.in)/2])
+				io.WriteString(c, g.in[:len(g.in)/2])
 				c.Sum(nil)
 				io.WriteString(c, g.in[len(g.in)/2:])
 			} else if j > 2 {

src/crypto/sha1/sha1_test.go

@@ -74,7 +74,7 @@ func TestGolden(t *testing.T) {
 				io.WriteString(c, g.in)
 				sum = c.Sum(nil)
 			case 2:
-				io.WriteString(c, g.in[0:len(g.in)/2])
+				io.WriteString(c, g.in[:len(g.in)/2])
 				c.Sum(nil)
 				io.WriteString(c, g.in[len(g.in)/2:])
 				sum = c.Sum(nil)
@@ -82,7 +82,7 @@ func TestGolden(t *testing.T) {
 				if boring.Enabled {
 					continue
 				}
-				io.WriteString(c, g.in[0:len(g.in)/2])
+				io.WriteString(c, g.in[:len(g.in)/2])
 				c.(*digest).ConstantTimeSum(nil)
 				io.WriteString(c, g.in[len(g.in)/2:])
 				sum = c.(*digest).ConstantTimeSum(nil)

src/crypto/sha256/sha256_test.go

@@ -104,7 +104,7 @@ func TestGolden(t *testing.T) {
 			if j < 2 {
 				io.WriteString(c, g.in)
 			} else {
-				io.WriteString(c, g.in[0:len(g.in)/2])
+				io.WriteString(c, g.in[:len(g.in)/2])
 				c.Sum(nil)
 				io.WriteString(c, g.in[len(g.in)/2:])
 			}
@@ -126,7 +126,7 @@ func TestGolden(t *testing.T) {
 			if j < 2 {
 				io.WriteString(c, g.in)
 			} else {
-				io.WriteString(c, g.in[0:len(g.in)/2])
+				io.WriteString(c, g.in[:len(g.in)/2])
 				c.Sum(nil)
 				io.WriteString(c, g.in[len(g.in)/2:])
 			}

src/crypto/subtle/constant_time_test.go

@@ -78,9 +78,9 @@ func TestConstantTimeEq(t *testing.T) {
 
 func makeCopy(v int, x, y []byte) []byte {
 	if len(x) > len(y) {
-		x = x[0:len(y)]
+		x = x[:len(y)]
 	} else {
-		y = y[0:len(x)]
+		y = y[:len(x)]
 	}
 	if v == 1 {
 		copy(x, y)
@@ -90,9 +90,9 @@ func makeCopy(v int, x, y []byte) []byte {
 
 func constantTimeCopyWrapper(v int, x, y []byte) []byte {
 	if len(x) > len(y) {
-		x = x[0:len(y)]
+		x = x[:len(y)]
 	} else {
-		y = y[0:len(x)]
+		y = y[:len(x)]
 	}
 	v &= 1
 	ConstantTimeCopy(v, x, y)

src/go/internal/gccgoimporter/parser.go

@@ -176,7 +176,7 @@ func (p *parser) parseQualifiedNameStr(unquotedName string) (pkgpath, name strin
 		name = parts[0]
 	default:
 		// qualified name, which may contain periods
-		pkgpath = strings.Join(parts[0:len(parts)-1], ".")
+		pkgpath = strings.Join(parts[:len(parts)-1], ".")
 		name = parts[len(parts)-1]
 	}
 

src/internal/stringslite/strings.go

@@ -14,7 +14,7 @@ import (
 )
 
 func HasPrefix(s, prefix string) bool {
-	return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
+	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
 }
 
 func HasSuffix(s, suffix string) bool {

src/math/big/natdiv.go

@@ -602,7 +602,7 @@ func (z nat) divLarge(u, uIn, vIn nat) (q, r nat) {
 	v := *vp
 	shlVU(v, vIn, shift)
 	u = u.make(len(uIn) + 1)
-	u[len(uIn)] = shlVU(u[0:len(uIn)], uIn, shift)
+	u[len(uIn)] = shlVU(u[:len(uIn)], uIn, shift)
 
 	// The caller should not pass aliased z and u, since those are
 	// the two different outputs, but correct just in case.
@@ -884,7 +884,7 @@ func (z nat) divRecursiveStep(u, v nat, depth int, tmp *nat, temps []*nat) {
 	if qhatv.cmp(u.norm()) > 0 {
 		panic("impossible")
 	}
-	c := subVV(u[0:len(qhatv)], u[0:len(qhatv)], qhatv)
+	c := subVV(u[:len(qhatv)], u[:len(qhatv)], qhatv)
 	if c > 0 {
 		c = subVW(u[len(qhatv):], u[len(qhatv):], c)
 	}

src/net/http/client_test.go

@@ -751,7 +751,7 @@ func testStreamingGet(t *testing.T, mode testMode) {
 	var buf [10]byte
 	for _, str := range []string{"i", "am", "also", "known", "as", "comet"} {
 		say <- str
-		n, err := io.ReadFull(res.Body, buf[0:len(str)])
+		n, err := io.ReadFull(res.Body, buf[:len(str)])
 		if err != nil {
 			t.Fatalf("ReadFull on %q: %v", str, err)
 		}

src/regexp/syntax/parse.go

@@ -621,7 +621,7 @@ func (p *parser) factor(sub []*Regexp) []*Regexp {
 		}
 
 		// Found end of a run with common leading literal string:
-		// sub[start:i] all begin with str[0:len(str)], but sub[i]
+		// sub[start:i] all begin with str[:len(str)], but sub[i]
 		// does not even begin with str[0].
 		//
 		// Factor out common string and append factored expression to out.

src/slices/slices.go

@@ -434,7 +434,7 @@ func rotateRight[E any](s []E, r int) {
 	rotateLeft(s, len(s)-r)
 }
 
-// overlaps reports whether the memory ranges a[0:len(a)] and b[0:len(b)] overlap.
+// overlaps reports whether the memory ranges a[:len(a)] and b[:len(b)] overlap.
 func overlaps[E any](a, b []E) bool {
 	if len(a) == 0 || len(b) == 0 {
 		return false

src/time/format.go

@@ -405,7 +405,7 @@ func match(s1, s2 string) bool {
 
 func lookup(tab []string, val string) (int, string, error) {
 	for i, v := range tab {
-		if len(val) >= len(v) && match(val[0:len(v)], v) {
+		if len(val) >= len(v) && match(val[:len(v)], v) {
 			return i, val[len(v):], nil
 		}
 	}

src/unicode/utf8/utf8_test.go

@@ -170,7 +170,7 @@ func TestDecodeRune(t *testing.T) {
 		}
 		r, size = DecodeRune(b[0 : len(b)-1])
 		if r != RuneError || size != wantsize {
-			t.Errorf("DecodeRune(%q) = %#04x, %d want %#04x, %d", b[0:len(b)-1], r, size, RuneError, wantsize)
+			t.Errorf("DecodeRune(%q) = %#04x, %d want %#04x, %d", b[:len(b)-1], r, size, RuneError, wantsize)
 		}
 		s = m.str[0 : len(m.str)-1]
 		r, size = DecodeRuneInString(s)