all: replace strings.Split with strings.SplitSeq

In Go 1.25+, strings.SplitSeq offers better
performance. Here are the benchmark results comparing
strings.Split and strings.SplitSeq in a for-loop, with the
benchmark code located in src/strings/iter_test.go:

goos: darwin
goarch: amd64
pkg: cmd/go/internal/auth
cpu: Intel(R) Core(TM) i7-8569U CPU @ 2.80GHz
                         │   old.txt   │               new.txt                │
                         │   sec/op    │    sec/op     vs base                │
ParseGitAuth/standard-8    281.4n ± 1%   218.0n ± 11%  -22.54% (p=0.000 n=10)
ParseGitAuth/with_url-8    549.1n ± 1%   480.5n ± 13%  -12.48% (p=0.002 n=10)
ParseGitAuth/minimal-8     235.4n ± 1%   197.3n ±  7%  -16.20% (p=0.000 n=10)
ParseGitAuth/complex-8     797.6n ± 2%   805.2n ±  4%        ~ (p=0.481 n=10)
ParseGitAuth/empty-8       87.48n ± 3%   63.25n ±  6%  -27.71% (p=0.000 n=10)
ParseGitAuth/malformed-8   228.8n ± 1%   171.2n ±  3%  -25.17% (p=0.000 n=10)
geomean                    288.9n        237.7n        -17.72%

                         │   old.txt   │              new.txt               │
                         │    B/op     │    B/op     vs base                │
ParseGitAuth/standard-8    192.00 ± 0%   96.00 ± 0%  -50.00% (p=0.000 n=10)
ParseGitAuth/with_url-8     400.0 ± 0%   288.0 ± 0%  -28.00% (p=0.000 n=10)
ParseGitAuth/minimal-8     144.00 ± 0%   80.00 ± 0%  -44.44% (p=0.000 n=10)
ParseGitAuth/complex-8      528.0 ± 0%   400.0 ± 0%  -24.24% (p=0.000 n=10)
ParseGitAuth/empty-8        32.00 ± 0%   16.00 ± 0%  -50.00% (p=0.000 n=10)
ParseGitAuth/malformed-8   176.00 ± 0%   80.00 ± 0%  -54.55% (p=0.000 n=10)
geomean                     179.0        102.1       -42.96%

                         │  old.txt   │              new.txt               │
                         │ allocs/op  │ allocs/op   vs base                │
ParseGitAuth/standard-8    3.000 ± 0%   2.000 ± 0%  -33.33% (p=0.000 n=10)
ParseGitAuth/with_url-8    4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
ParseGitAuth/minimal-8     3.000 ± 0%   2.000 ± 0%  -33.33% (p=0.000 n=10)
ParseGitAuth/complex-8     4.000 ± 0%   3.000 ± 0%  -25.00% (p=0.000 n=10)
ParseGitAuth/empty-8       2.000 ± 0%   1.000 ± 0%  -50.00% (p=0.000 n=10)
ParseGitAuth/malformed-8   3.000 ± 0%   2.000 ± 0%  -33.33% (p=0.000 n=10)
geomean                    3.086        2.040       -33.91%

Updates #69315.

Change-Id: Id0219edea45d9658d527b863162ebe917e7821d9
GitHub-Last-Rev: 392b315e12
GitHub-Pull-Request: golang/go#75259
Reviewed-on: https://go-review.googlesource.com/c/go/+/701015
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Emmanuel Odeke <emmanuel@orijtech.com>

misc/ios/go_ios_exec.go

@@ -212,7 +212,7 @@ func copyLocalData(dstbase string) (pkgpath string, err error) {
 	// Copy all immediate files and testdata directories between
 	// the package being tested and the source root.
 	pkgpath = ""
-	for _, element := range strings.Split(finalPkgpath, string(filepath.Separator)) {
+	for element := range strings.SplitSeq(finalPkgpath, string(filepath.Separator)) {
 		if debug {
 			log.Printf("copying %s", pkgpath)
 		}

src/cmd/cgo/gcc.go

@@ -251,7 +251,7 @@ func (f *File) loadDefines(gccOptions []string) bool {
 	stdout := gccDefines(b.Bytes(), gccOptions)
 
 	var gccIsClang bool
-	for _, line := range strings.Split(stdout, "\n") {
+	for line := range strings.SplitSeq(stdout, "\n") {
 		if len(line) < 9 || line[0:7] != "#define" {
 			continue
 		}
@@ -428,7 +428,7 @@ func (p *Package) guessKinds(f *File) []*Name {
 		notDeclared
 	)
 	sawUnmatchedErrors := false
-	for _, line := range strings.Split(stderr, "\n") {
+	for line := range strings.SplitSeq(stderr, "\n") {
 		// Ignore warnings and random comments, with one
 		// exception: newer GCC versions will sometimes emit
 		// an error on a macro #define with a note referring

src/cmd/cgo/internal/test/testx.go

@@ -447,7 +447,7 @@ func issue7978check(t *testing.T, wantFunc string, badFunc string, depth int) {
 	runtime.GC()
 	buf := make([]byte, 65536)
 	trace := string(buf[:runtime.Stack(buf, true)])
-	for _, goroutine := range strings.Split(trace, "\n\n") {
+	for goroutine := range strings.SplitSeq(trace, "\n\n") {
 		if strings.Contains(goroutine, "test.issue7978go") {
 			trace := strings.Split(goroutine, "\n")
 			// look for the expected function in the stack

src/cmd/compile/internal/base/flag.go

@@ -570,7 +570,7 @@ func readEmbedCfg(file string) {
 
 // parseSpectre parses the spectre configuration from the string s.
 func parseSpectre(s string) {
-	for _, f := range strings.Split(s, ",") {
+	for f := range strings.SplitSeq(s, ",") {
 		f = strings.TrimSpace(f)
 		switch f {
 		default:

src/cmd/dist/build.go

@@ -380,7 +380,7 @@ func findgoversion() string {
 		if i := strings.Index(b, "\n"); i >= 0 {
 			rest := b[i+1:]
 			b = chomp(b[:i])
-			for _, line := range strings.Split(rest, "\n") {
+			for line := range strings.SplitSeq(rest, "\n") {
 				f := strings.Fields(line)
 				if len(f) == 0 {
 					continue
@@ -1137,7 +1137,7 @@ func shouldbuild(file, pkg string) bool {
 	}
 
 	// Check file contents for //go:build lines.
-	for _, p := range strings.Split(readfile(file), "\n") {
+	for p := range strings.SplitSeq(readfile(file), "\n") {
 		p = strings.TrimSpace(p)
 		if p == "" {
 			continue
@@ -2016,7 +2016,7 @@ func cmdlist() {
 }
 
 func setNoOpt() {
-	for _, gcflag := range strings.Split(gogcflags, " ") {
+	for gcflag := range strings.SplitSeq(gogcflags, " ") {
 		if gcflag == "-N" || gcflag == "-l" {
 			noOpt = true
 			break

src/cmd/distpack/pack.go

@@ -271,7 +271,7 @@ func readVERSION(goroot string) (version string, t time.Time) {
 		log.Fatal(err)
 	}
 	version, rest, _ := strings.Cut(string(data), "\n")
-	for _, line := range strings.Split(rest, "\n") {
+	for line := range strings.SplitSeq(rest, "\n") {
 		f := strings.Fields(line)
 		if len(f) == 0 {
 			continue

src/cmd/fix/main.go

@@ -84,14 +84,14 @@ func main() {
 
 	if *allowedRewrites != "" {
 		allowed = make(map[string]bool)
-		for _, f := range strings.Split(*allowedRewrites, ",") {
+		for f := range strings.SplitSeq(*allowedRewrites, ",") {
 			allowed[f] = true
 		}
 	}
 
 	if *forceRewrites != "" {
 		force = make(map[string]bool)
-		for _, f := range strings.Split(*forceRewrites, ",") {
+		for f := range strings.SplitSeq(*forceRewrites, ",") {
 			force[f] = true
 		}
 	}

src/cmd/go/internal/auth/gitauth.go

@@ -82,7 +82,7 @@ func runGitAuth(client *http.Client, dir, url string) (string, http.Header, erro
 // Any of these values may be empty if parsing fails.
 func parseGitAuth(data []byte) (parsedPrefix, username, password string) {
 	prefix := new(url.URL)
-	for _, line := range strings.Split(string(data), "\n") {
+	for line := range strings.SplitSeq(string(data), "\n") {
 		key, value, ok := strings.Cut(strings.TrimSpace(line), "=")
 		if !ok {
 			continue

src/cmd/go/internal/auth/gitauth_test.go

@@ -5,6 +5,7 @@
 package auth
 
 import (
+	"strings"
 	"testing"
 )
 
@@ -82,3 +83,77 @@ password:secr3t
 		}
 	}
 }
+
+func BenchmarkParseGitAuth(b *testing.B) {
+	// Define different test scenarios to benchmark
+	testCases := []struct {
+		name string
+		data []byte
+	}{{
+		// Standard scenario with all basic fields present
+		name: "standard",
+		data: []byte(`
+protocol=https
+host=example.com
+username=bob
+password=secr3t
+`),
+	}, {
+		// Scenario with URL field included
+		name: "with_url",
+		data: []byte(`
+protocol=https
+host=example.com
+username=bob
+password=secr3t
+url=https://example.com/repo
+`),
+	}, {
+		// Minimal scenario with only required fields
+		name: "minimal",
+		data: []byte(`
+protocol=https
+host=example.com
+`),
+	}, {
+		// Complex scenario with longer values and extra fields
+		name: "complex",
+		data: func() []byte {
+			var builder strings.Builder
+			builder.WriteString("protocol=https\n")
+			builder.WriteString("host=example.com\n")
+			builder.WriteString("username=longusernamenamename\n")
+			builder.WriteString("password=longpasswordwithmanycharacters123456789\n")
+			builder.WriteString("url=https://example.com/very/long/path/to/repository\n")
+			builder.WriteString("extra1=value1\n")
+			builder.WriteString("extra2=value2\n")
+			return []byte(builder.String())
+		}(),
+	}, {
+		// Scenario with empty input
+		name: "empty",
+		data: []byte(``),
+	}, {
+		// Scenario with malformed input (using colon instead of equals)
+		name: "malformed",
+		data: []byte(`
+protocol:https
+host:example.com
+username:bob
+password:secr3t
+`),
+	}}
+
+	for _, tc := range testCases {
+		b.Run(tc.name, func(b *testing.B) {
+			b.ResetTimer()
+			for b.Loop() {
+				prefix, username, password := parseGitAuth(tc.data)
+
+				_ = prefix
+				_ = username
+				_ = password
+			}
+		})
+	}
+}

src/cmd/go/internal/auth/netrc.go

@@ -24,7 +24,7 @@ func parseNetrc(data string) []netrcLine {
 	var nrc []netrcLine
 	var l netrcLine
 	inMacro := false
-	for _, line := range strings.Split(data, "\n") {
+	for line := range strings.SplitSeq(data, "\n") {
 		if inMacro {
 			if line == "" {
 				inMacro = false

src/cmd/go/internal/doc/dirs.go

@@ -241,7 +241,7 @@ func findCodeRoots() []Dir {
 	cmd := exec.Command(goCmd(), "list", "-m", "-f={{.Path}}\t{{.Dir}}", "all")
 	cmd.Stderr = os.Stderr
 	out, _ := cmd.Output()
-	for _, line := range strings.Split(string(out), "\n") {
+	for line := range strings.SplitSeq(string(out), "\n") {
 		path, dir, _ := strings.Cut(line, "\t")
 		if dir != "" {
 			list = append(list, Dir{importPath: path, dir: dir, inModule: true})

src/cmd/go/internal/doc/pkg.go

@@ -920,7 +920,7 @@ func trimUnexportedFields(fields *ast.FieldList, isInterface bool) *ast.FieldLis
 
 			start := doc.List[0].Slash
 			doc.List = doc.List[:0]
-			for _, line := range strings.Split(text, "\n") {
+			for line := range strings.SplitSeq(text, "\n") {
 				prefix := "// "
 				if len(line) > 0 && line[0] == '\t' {
 					prefix = "//"

src/cmd/go/internal/list/list.go

@@ -381,7 +381,7 @@ func (v *jsonFlag) Set(s string) error {
 	if *v == nil {
 		*v = make(map[string]bool)
 	}
-	for _, f := range strings.Split(s, ",") {
+	for f := range strings.SplitSeq(s, ",") {
 		(*v)[f] = true
 	}
 	return nil

src/cmd/go/internal/modfetch/codehost/git.go

@@ -173,7 +173,7 @@ func (r *gitRepo) loadLocalTags(ctx context.Context) {
 		return
 	}
 
-	for _, line := range strings.Split(string(out), "\n") {
+	for line := range strings.SplitSeq(string(out), "\n") {
 		if line != "" {
 			r.localTags.Store(line, true)
 		}
@@ -273,7 +273,7 @@ func (r *gitRepo) loadRefs(ctx context.Context) (map[string]string, error) {
 		}
 
 		refs := make(map[string]string)
-		for _, line := range strings.Split(string(out), "\n") {
+		for line := range strings.SplitSeq(string(out), "\n") {
 			f := strings.Fields(line)
 			if len(f) != 2 {
 				continue
@@ -745,7 +745,7 @@ func (r *gitRepo) RecentTag(ctx context.Context, rev, prefix string, allowed fun
 
 		// prefixed tags aren't valid semver tags so compare without prefix, but only tags with correct prefix
 		var highest string
-		for _, line := range strings.Split(string(out), "\n") {
+		for line := range strings.SplitSeq(string(out), "\n") {
 			line = strings.TrimSpace(line)
 			// git do support lstrip in for-each-ref format, but it was added in v2.13.0. Stripping here
 			// instead gives support for git v2.7.0.

src/cmd/go/internal/modfetch/codehost/vcs.go

@@ -561,7 +561,7 @@ func bzrParseStat(rev, out string) (*RevInfo, error) {
 	var revno int64
 	var tm time.Time
 	var tags []string
-	for _, line := range strings.Split(out, "\n") {
+	for line := range strings.SplitSeq(out, "\n") {
 		if line == "" || line[0] == ' ' || line[0] == '\t' {
 			// End of header, start of commit message.
 			break
@@ -614,7 +614,7 @@ func bzrParseStat(rev, out string) (*RevInfo, error) {
 }
 
 func fossilParseStat(rev, out string) (*RevInfo, error) {
-	for _, line := range strings.Split(out, "\n") {
+	for line := range strings.SplitSeq(out, "\n") {
 		if strings.HasPrefix(line, "uuid:") || strings.HasPrefix(line, "hash:") {
 			f := strings.Fields(line)
 			if len(f) != 5 || len(f[1]) != 40 || f[4] != "UTC" {

src/cmd/go/internal/modindex/build.go

@@ -426,7 +426,7 @@ Lines:
 // These lines set CFLAGS, CPPFLAGS, CXXFLAGS and LDFLAGS and pkg-config directives
 // that affect the way cgo's C code is built.
 func (ctxt *Context) saveCgo(filename string, di *build.Package, text string) error {
-	for _, line := range strings.Split(text, "\n") {
+	for line := range strings.SplitSeq(text, "\n") {
 		orig := line
 
 		// Line is

src/cmd/go/internal/modindex/scan.go

@@ -275,7 +275,7 @@ func importRaw(modroot, reldir string) *rawPackage {
 // which is the comment on import "C".
 func extractCgoDirectives(doc string) []string {
 	var out []string
-	for _, line := range strings.Split(doc, "\n") {
+	for line := range strings.SplitSeq(doc, "\n") {
 		// Line is
 		//	#cgo [GOOS/GOARCH...] LDFLAGS: stuff
 		//

src/cmd/go/internal/modload/buildlist.go

@@ -329,7 +329,7 @@ func readModGraph(ctx context.Context, pruning modPruning, roots []module.Versio
 		// so it wouldn't be useful to log when that occurs (because it happens in
 		// normal operation all the time).
 		readModGraphDebugOnce.Do(func() {
-			for _, f := range strings.Split(os.Getenv("GODEBUG"), ",") {
+			for f := range strings.SplitSeq(os.Getenv("GODEBUG"), ",") {
 				switch f {
 				case "lazymod=log":
 					debug.PrintStack()

src/cmd/go/internal/modload/init.go

@@ -1597,7 +1597,7 @@ func modulesTextIsForWorkspace(vendorDir string) (bool, error) {
 	}
 	line, _, _ := strings.Cut(string(buf[:n]), "\n")
 	if annotations, ok := strings.CutPrefix(line, "## "); ok {
-		for _, entry := range strings.Split(annotations, ";") {
+		for entry := range strings.SplitSeq(annotations, ";") {
 			entry = strings.TrimSpace(entry)
 			if entry == "workspace" {
 				return true, nil

src/cmd/go/internal/modload/vendor.go

@@ -53,7 +53,7 @@ func readVendorList(vendorDir string) {
 		}
 
 		var mod module.Version
-		for _, line := range strings.Split(string(data), "\n") {
+		for line := range strings.SplitSeq(string(data), "\n") {
 			if strings.HasPrefix(line, "# ") {
 				f := strings.Fields(line)
 
@@ -103,7 +103,7 @@ func readVendorList(vendorDir string) {
 			if annotations, ok := strings.CutPrefix(line, "## "); ok {
 				// Metadata. Take the union of annotations across multiple lines, if present.
 				meta := vendorMeta[mod]
-				for _, entry := range strings.Split(annotations, ";") {
+				for entry := range strings.SplitSeq(annotations, ";") {
 					entry = strings.TrimSpace(entry)
 					if entry == "explicit" {
 						meta.Explicit = true

src/cmd/go/internal/test/testflag.go

@@ -149,7 +149,7 @@ func (f *vetFlag) Set(value string) error {
 
 	*f = vetFlag{explicit: true}
 	var single string
-	for _, arg := range strings.Split(value, ",") {
+	for arg := range strings.SplitSeq(value, ",") {
 		switch arg {
 		case "":
 			return fmt.Errorf("-vet argument contains empty list element")

src/cmd/go/internal/toolchain/path_windows.go

@@ -21,7 +21,7 @@ var pathExts = sync.OnceValue(func() []string {
 	}
 
 	var exts []string
-	for _, e := range strings.Split(strings.ToLower(x), `;`) {
+	for e := range strings.SplitSeq(strings.ToLower(x), `;`) {
 		if e == "" {
 			continue
 		}

src/cmd/go/internal/vcs/vcs.go

@@ -110,7 +110,7 @@ func (v *Cmd) isSecureScheme(scheme string) bool {
 		// colon-separated list of schemes that are allowed to be used with git
 		// fetch/clone. Any scheme not mentioned will be considered insecure.
 		if allow := os.Getenv("GIT_ALLOW_PROTOCOL"); allow != "" {
-			for _, s := range strings.Split(allow, ":") {
+			for s := range strings.SplitSeq(allow, ":") {
 				if s == scheme {
 					return true
 				}
@@ -440,7 +440,7 @@ func bzrStatus(vcsBzr *Cmd, rootDir string) (Status, error) {
 	var rev string
 	var commitTime time.Time
 
-	for _, line := range strings.Split(out, "\n") {
+	for line := range strings.SplitSeq(out, "\n") {
 		i := strings.IndexByte(line, ':')
 		if i < 0 {
 			continue
@@ -974,7 +974,7 @@ func parseGOVCS(s string) (govcsConfig, error) {
 	}
 	var cfg govcsConfig
 	have := make(map[string]string)
-	for _, item := range strings.Split(s, ",") {
+	for item := range strings.SplitSeq(s, ",") {
 		item = strings.TrimSpace(item)
 		if item == "" {
 			return nil, fmt.Errorf("empty entry in GOVCS")

src/cmd/go/internal/vcweb/vcweb.go

@@ -224,7 +224,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	// uniqueness: if a path exists as a directory, then it cannot exist as a
 	// ".txt" script (because the search would ignore that file).
 	scriptPath := "."
-	for _, part := range strings.Split(clean, "/") {
+	for part := range strings.SplitSeq(clean, "/") {
 		scriptPath = filepath.Join(scriptPath, part)
 		dir := filepath.Join(s.scriptDir, scriptPath)
 		if _, err := os.Stat(dir); err != nil {

src/cmd/go/internal/work/build.go

@@ -384,7 +384,7 @@ func (v *tagsFlag) Set(s string) error {
 
 	// Split on commas, ignore empty strings.
 	*v = []string{}
-	for _, s := range strings.Split(s, ",") {
+	for s := range strings.SplitSeq(s, ",") {
 		if s != "" {
 			*v = append(*v, s)
 		}

src/cmd/go/internal/work/exec.go

@@ -1122,7 +1122,7 @@ func (b *Builder) loadCachedVet(a *Action) error {
 		return fmt.Errorf("reading srcfiles list: %w", err)
 	}
 	var srcfiles []string
-	for _, name := range strings.Split(string(list), "\n") {
+	for name := range strings.SplitSeq(string(list), "\n") {
 		if name == "" { // end of list
 			continue
 		}
@@ -1146,7 +1146,7 @@ func (b *Builder) loadCachedCompiledGoFiles(a *Action) error {
 		return fmt.Errorf("reading srcfiles list: %w", err)
 	}
 	var gofiles []string
-	for _, name := range strings.Split(string(list), "\n") {
+	for name := range strings.SplitSeq(string(list), "\n") {
 		if name == "" { // end of list
 			continue
 		} else if !strings.HasSuffix(name, ".go") {

src/cmd/go/internal/work/gccgo.go

@@ -278,7 +278,7 @@ func (tools gccgoToolchain) link(b *Builder, root *Action, out, importcfg string
 			return err
 		}
 		const ldflagsPrefix = "_CGO_LDFLAGS="
-		for _, line := range strings.Split(string(flags), "\n") {
+		for line := range strings.SplitSeq(string(flags), "\n") {
 			if strings.HasPrefix(line, ldflagsPrefix) {
 				flag := line[len(ldflagsPrefix):]
 				// Every _cgo_flags file has -g and -O2 in _CGO_LDFLAGS

src/cmd/internal/objabi/flag.go

@@ -277,7 +277,7 @@ func (f *DebugFlag) Set(debugstr string) error {
 	if debugstr == "" {
 		return nil
 	}
-	for _, name := range strings.Split(debugstr, ",") {
+	for name := range strings.SplitSeq(debugstr, ",") {
 		if name == "" {
 			continue
 		}

src/cmd/internal/script/cmds.go

@@ -513,7 +513,7 @@ func lookPath(s *State, command string) (string, error) {
 	}
 
 	pathEnv, _ := s.LookupEnv(pathEnvName())
-	for _, dir := range strings.Split(pathEnv, string(filepath.ListSeparator)) {
+	for dir := range strings.SplitSeq(pathEnv, string(filepath.ListSeparator)) {
 		if dir == "" {
 			continue
 		}

src/cmd/internal/script/scripttest/conditions.go

@@ -88,7 +88,7 @@ func pieLinkExt(s *script.State) (bool, error) {
 
 func hasGodebug(s *script.State, value string) (bool, error) {
 	godebug, _ := s.LookupEnv("GODEBUG")
-	for _, p := range strings.Split(godebug, ",") {
+	for p := range strings.SplitSeq(godebug, ",") {
 		if strings.TrimSpace(p) == value {
 			return true, nil
 		}

src/go/ast/ast.go

@@ -1123,7 +1123,7 @@ func generator(file *File) (string, bool) {
 			// opt: check Contains first to avoid unnecessary array allocation in Split.
 			const prefix = "// Code generated "
 			if strings.Contains(comment.Text, prefix) {
-				for _, line := range strings.Split(comment.Text, "\n") {
+				for line := range strings.SplitSeq(comment.Text, "\n") {
 					if rest, ok := strings.CutPrefix(line, prefix); ok {
 						if gen, ok := strings.CutSuffix(rest, " DO NOT EDIT."); ok {
 							return gen, true

src/go/build/build.go

@@ -1708,7 +1708,7 @@ Lines:
 // that affect the way cgo's C code is built.
 func (ctxt *Context) saveCgo(filename string, di *Package, cg *ast.CommentGroup) error {
 	text := cg.Text()
-	for _, line := range strings.Split(text, "\n") {
+	for line := range strings.SplitSeq(text, "\n") {
 		orig := line
 
 		// Line is

src/go/build/constraint/expr.go

@@ -406,9 +406,9 @@ func parsePlusBuildExpr(text string) (Expr, error) {
 	size := 0
 
 	var x Expr
-	for _, clause := range strings.Fields(text) {
+	for clause := range strings.FieldsSeq(text) {
 		var y Expr
-		for _, lit := range strings.Split(clause, ",") {
+		for lit := range strings.SplitSeq(clause, ",") {
 			var z Expr
 			var neg bool
 			if strings.HasPrefix(lit, "!!") || lit == "!" {

src/internal/buildcfg/cfg.go

@@ -336,7 +336,7 @@ func (f gowasmFeatures) String() string {
 }
 
 func gowasm() (f gowasmFeatures) {
-	for _, opt := range strings.Split(envOr("GOWASM", ""), ",") {
+	for opt := range strings.SplitSeq(envOr("GOWASM", ""), ",") {
 		switch opt {
 		case "satconv":
 			f.SatConv = true

src/internal/buildcfg/exp.go

@@ -113,7 +113,7 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
 		}
 
 		// Parse names.
-		for _, f := range strings.Split(goexp, ",") {
+		for f := range strings.SplitSeq(goexp, ",") {
 			if f == "" {
 				continue
 			}

src/internal/testenv/testenv.go

@@ -489,7 +489,7 @@ func WriteImportcfg(t testing.TB, dstPath string, packageFiles map[string]string
 			t.Fatalf("%v: %v\n%s", cmd, err, cmd.Stderr)
 		}
 
-		for _, line := range strings.Split(string(out), "\n") {
+		for line := range strings.SplitSeq(string(out), "\n") {
 			if line == "" {
 				continue
 			}

src/internal/trace/traceviewer/mmu.go

@@ -69,7 +69,7 @@ var utilFlagNames = map[string]trace.UtilFlags{
 
 func requestUtilFlags(r *http.Request) trace.UtilFlags {
 	var flags trace.UtilFlags
-	for _, flagStr := range strings.Split(r.FormValue("flags"), "|") {
+	for flagStr := range strings.SplitSeq(r.FormValue("flags"), "|") {
 		flags |= utilFlagNames[flagStr]
 	}
 	return flags
@@ -119,7 +119,7 @@ func (m *mmu) HandlePlot(w http.ResponseWriter, r *http.Request) {
 	}
 
 	var quantiles []float64
-	for _, flagStr := range strings.Split(r.FormValue("flags"), "|") {
+	for flagStr := range strings.SplitSeq(r.FormValue("flags"), "|") {
 		if flagStr == "mut" {
 			quantiles = []float64{0, 1 - .999, 1 - .99, 1 - .95}
 			break

src/os/exec/lp_windows.go

@@ -123,7 +123,7 @@ func pathExt() []string {
 	var exts []string
 	x := os.Getenv(`PATHEXT`)
 	if x != "" {
-		for _, e := range strings.Split(strings.ToLower(x), `;`) {
+		for e := range strings.SplitSeq(strings.ToLower(x), `;`) {
 			if e == "" {
 				continue
 			}

src/strings/iter_test.go

@@ -50,3 +50,56 @@ func BenchmarkSplitAfterSeqMultiByteSeparator(b *testing.B) {
 		}
 	}
 }
+
+func findKvBySplit(s string, k string) string {
+	for _, kv := range Split(s, ",") {
+		if HasPrefix(kv, k) {
+			return kv
+		}
+	}
+	return ""
+}
+
+func findKvBySplitSeq(s string, k string) string {
+	for kv := range SplitSeq(s, ",") {
+		if HasPrefix(kv, k) {
+			return kv
+		}
+	}
+	return ""
+}
+
+func BenchmarkSplitAndSplitSeq(b *testing.B) {
+	testSplitString := "k1=v1,k2=v2,k3=v3,k4=v4"
+	testCases := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "Key found",
+			input: "k3",
+		},
+		{
+			name:  "Key not found",
+			input: "k100",
+		},
+	}
+
+	for _, testCase := range testCases {
+		b.Run("bySplit "+testCase.name, func(b *testing.B) {
+			b.ResetTimer()
+			b.ReportAllocs()
+			for b.Loop() {
+				findKvBySplit(testSplitString, testCase.input)
+			}
+		})
+
+		b.Run("bySplitSeq "+testCase.name, func(b *testing.B) {
+			b.ResetTimer()
+			b.ReportAllocs()
+			for b.Loop() {
+				findKvBySplitSeq(testSplitString, testCase.input)
+			}
+		})
+	}
+}