Kirill Kolyshkin (Gerrit)

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Dec 17, 2025, 8:03:31 PM (2 days ago) Dec 17

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Kirill Kolyshkin has uploaded the change for review

Commit message

all: replace strings.Index etc. with strings.Cut

Replaces certain patterns of use of strings.Index and string slicing by
strings.Cut, added in Go 1.18.

Generated by

	go fix -stringscut ./...
using

	go version go1.26-devel_ad85395442 Wed Dec 17 15:56:48 2025 -0800 linux/amd64

Change-Id: Ibb02f7510b7576ead9a78b632cbc7ac1349419d3

Change diff

diff --git a/src/archive/tar/strconv.go b/src/archive/tar/strconv.go
index 217efe9..b0ac619 100644
--- a/src/archive/tar/strconv.go
+++ b/src/archive/tar/strconv.go
@@ -53,8 +53,8 @@
 // parseString parses bytes as a NUL-terminated C-style string.
 // If a NUL byte is not found then the whole slice is returned as a string.
 func (*parser) parseString(b []byte) string {
-	if i := bytes.IndexByte(b, 0); i >= 0 {
-		return string(b[:i])
+	if before, _, ok := bytes.Cut(b, []byte{0}); ok {
+		return string(before)
 	}
 	return string(b)
 }
diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index 0b26b8e..5c29f6b 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -127,11 +127,11 @@
 }
 
 func (u *unmarshalerText) UnmarshalText(b []byte) error {
-	pos := bytes.IndexByte(b, ':')
-	if pos == -1 {
+	before, after, ok := bytes.Cut(b, []byte{':'})
+	if !ok {
 		return errors.New("missing separator")
 	}
-	u.A, u.B = string(b[:pos]), string(b[pos+1:])
+	u.A, u.B = string(before), string(after)
 	return nil
 }
 
diff --git a/src/go/doc/comment/parse.go b/src/go/doc/comment/parse.go
index 4d5784a..5e03012 100644
--- a/src/go/doc/comment/parse.go
+++ b/src/go/doc/comment/parse.go
@@ -679,8 +679,8 @@
 
 	text := line[1:i]
 	url := strings.TrimSpace(line[i+3:])
-	j := strings.Index(url, "://")
-	if j < 0 || !isScheme(url[:j]) {
+	before, _, ok := strings.Cut(url, "://")
+	if !ok || !isScheme(before) {
 		return nil, false
 	}
 
diff --git a/src/go/doc/example.go b/src/go/doc/example.go
index 8c01bf0..9ba5460 100644
--- a/src/go/doc/example.go
+++ b/src/go/doc/example.go
@@ -689,8 +689,8 @@
 //
 // Adapted from debug/gosym/symtab.go:Sym.nameWithoutInst.
 func nameWithoutInst(name string) string {
-	start := strings.Index(name, "[")
-	if start < 0 {
+	before, _, ok := strings.Cut(name, "[")
+	if !ok {
 		return name
 	}
 	end := strings.LastIndex(name, "]")
@@ -698,7 +698,7 @@
 		// Malformed name, should contain closing bracket too.
 		return name
 	}
-	return name[0:start] + name[end+1:]
+	return before + name[end+1:]
 }
 
 // splitExampleName attempts to split example name s at index i,
diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
index a7e041e..ee31012 100644
--- a/src/go/types/api_test.go
+++ b/src/go/types/api_test.go
@@ -62,8 +62,8 @@
 // pkgName extracts the package name from src, which must contain a package header.
 func pkgName(src string) string {
 	const kw = "package "
-	if i := strings.Index(src, kw); i >= 0 {
-		after := src[i+len(kw):]
+	if _, after, ok := strings.Cut(src, kw); ok {
+		after := after
 		n := len(after)
 		if i := strings.IndexAny(after, "\n\t ;/"); i >= 0 {
 			n = i
diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 44e4fd0..e83cfdc 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -109,7 +109,7 @@
 		return nil // first line is not a line comment
 	}
 	src = src[len(prefix):]
-	if i := bytes.Index(src, []byte("-")); i < 0 || len(bytes.TrimSpace(src[:i])) != 0 {
+	if before, _, ok := bytes.Cut(src, []byte("-")); !ok || len(bytes.TrimSpace(before)) != 0 {
 		return nil // comment doesn't start with a "-"
 	}
 	end := bytes.Index(src, []byte("\n"))
diff --git a/src/html/template/css.go b/src/html/template/css.go
index f650d8b..79789c7 100644
--- a/src/html/template/css.go
+++ b/src/html/template/css.go
@@ -56,8 +56,8 @@
 // backed by a new array.
 // https://www.w3.org/TR/css3-syntax/#SUBTOK-stringchar defines stringchar.
 func decodeCSS(s []byte) []byte {
-	i := bytes.IndexByte(s, '\\')
-	if i == -1 {
+	found := bytes.Contains(s, []byte{'\\'})
+	if !found {
 		return s
 	}
 	// The UTF-8 sequence for a codepoint is never longer than 1 + the
diff --git a/src/math/big/ratconv.go b/src/math/big/ratconv.go
index 229f31b..1d7f2d5 100644
--- a/src/math/big/ratconv.go
+++ b/src/math/big/ratconv.go
@@ -62,11 +62,11 @@
 	// len(s) > 0
 
 	// parse fraction a/b, if any
-	if sep := strings.Index(s, "/"); sep >= 0 {
-		if _, ok := z.a.SetString(s[:sep], 0); !ok {
+	if before, after, ok := strings.Cut(s, "/"); ok {
+		if _, ok := z.a.SetString(before, 0); !ok {
 			return nil, false
 		}
-		r := strings.NewReader(s[sep+1:])
+		r := strings.NewReader(after)
 		var err error
 		if z.b.abs, _, _, err = z.b.abs.scan(r, 0, false); err != nil {
 			return nil, false
diff --git a/src/testing/fstest/mapfs.go b/src/testing/fstest/mapfs.go
index 5ce0398..637a024 100644
--- a/src/testing/fstest/mapfs.go
+++ b/src/testing/fstest/mapfs.go
@@ -68,13 +68,13 @@
 	var need = make(map[string]bool)
 	if realName == "." {
 		for fname, f := range fsys {
-			i := strings.Index(fname, "/")
-			if i < 0 {
+			before, _, ok0 := strings.Cut(fname, "/")
+			if !ok0 {
 				if fname != "." {
 					list = append(list, mapFileInfo{fname, f})
 				}
 			} else {
-				need[fname[:i]] = true
+				need[before] = true
 			}
 		}
 	} else {
diff --git a/src/testing/fstest/testfs.go b/src/testing/fstest/testfs.go
index 72830a0..5efb027 100644
--- a/src/testing/fstest/testfs.go
+++ b/src/testing/fstest/testfs.go
@@ -615,12 +615,12 @@
 	if file == "." {
 		bad = append(bad, "/")
 	}
-	if i := strings.Index(file, "/"); i >= 0 {
+	if before, after, ok := strings.Cut(file, "/"); ok {
 		bad = append(bad,
-			file[:i]+"//"+file[i+1:],
-			file[:i]+"/./"+file[i+1:],
-			file[:i]+`\`+file[i+1:],
-			file[:i]+"/../"+file,
+			before+"//"+after,
+			before+"/./"+after,
+			before+`\`+after,
+			before+"/../"+file,
 		)
 	}
 	if i := strings.LastIndex(file, "/"); i >= 0 {

Change information

Files:

M src/archive/tar/strconv.go
M src/encoding/json/decode_test.go
M src/go/doc/comment/parse.go
M src/go/doc/example.go
M src/go/types/api_test.go
M src/go/types/check_test.go
M src/html/template/css.go
M src/math/big/ratconv.go
M src/testing/fstest/mapfs.go
M src/testing/fstest/testfs.go

Change size: M

Delta: 10 files changed, 26 insertions(+), 26 deletions(-)

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Kirill Kolyshkin (Gerrit)

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Dec 17, 2025, 8:08:37 PM (2 days ago) Dec 17

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Kirill Kolyshkin voted Commit-Queue+1

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Dec 18, 2025, 2:19:53 PM (20 hours ago) Dec 18

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Dec 18, 2025, 4:41:14 PM (18 hours ago) Dec 18

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Alan Donovan . resolved

Again, thanks for this CL and for the bug it discovered in rangeint, but I have to place it on hold until after the freeze (at which point it might be simplest to regenerate it).

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[go] all: replace strings.Index etc. with strings.Cut

Kirill Kolyshkin (Gerrit)

Kirill Kolyshkin has uploaded the change for review

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Change diff

Change information

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Kirill Kolyshkin (Gerrit)

Kirill Kolyshkin voted Commit-Queue+1

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Kirill Kolyshkin (Gerrit)

Kirill Kolyshkin voted Commit-Queue+1

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Alan Donovan (Gerrit)

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