cmd/go/internal: use strings.Cut

Change-Id: Icbe2af4f2abf22b6a8c9cec33f0f88018f3bd1c7
GitHub-Last-Rev: 81392a6e88d5297f958116031949b37f70271556
GitHub-Pull-Request: golang/go#55908
Reviewed-on: https://go-review.googlesource.com/c/go/+/435737
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>

12 files changed, 42 insertions, 62 deletions

diff --git a/src/cmd/go/internal/cmdflag/flag.go b/src/cmd/go/internal/cmdflag/flag.go
index a634bc1ab8..86e33ea111 100644
--- a/src/cmd/go/internal/cmdflag/flag.go
+++ b/src/cmd/go/internal/cmdflag/flag.go
@@ -70,14 +70,7 @@ func ParseOne(fs *flag.FlagSet, args []string) (f *flag.Flag, remainingArgs []st
 		return nil, args, NonFlagError{RawArg: raw}
 	}
 
-	name := arg[1:]
-	hasValue := false
-	value := ""
-	if i := strings.Index(name, "="); i >= 0 {
-		value = name[i+1:]
-		hasValue = true
-		name = name[0:i]
-	}
+	name, value, hasValue := strings.Cut(arg[1:], "=")
 
 	f = fs.Lookup(name)
 	if f == nil {
diff --git a/src/cmd/go/internal/envcmd/env.go b/src/cmd/go/internal/envcmd/env.go
index 2d8f7afd6b..f7f065529d 100644
--- a/src/cmd/go/internal/envcmd/env.go
+++ b/src/cmd/go/internal/envcmd/env.go
@@ -318,11 +318,10 @@ func runEnvW(args []string) {
 	}
 	add := make(map[string]string)
 	for _, arg := range args {
-		i := strings.Index(arg, "=")
-		if i < 0 {
+		key, val, found := strings.Cut(arg, "=")
+		if !found {
 			base.Fatalf("go: arguments must be KEY=VALUE: invalid argument: %s", arg)
 		}
-		key, val := arg[:i], arg[i+1:]
 		if err := checkEnvWrite(key, val); err != nil {
 			base.Fatalf("go: %v", err)
 		}
diff --git a/src/cmd/go/internal/modcmd/edit.go b/src/cmd/go/internal/modcmd/edit.go
index e5182a9590..edc1b19877 100644
--- a/src/cmd/go/internal/modcmd/edit.go
+++ b/src/cmd/go/internal/modcmd/edit.go
@@ -262,11 +262,11 @@ func runEdit(ctx context.Context, cmd *base.Command, args []string) {
 
 // parsePathVersion parses -flag=arg expecting arg to be path@version.
 func parsePathVersion(flag, arg string) (path, version string) {
-	i := strings.Index(arg, "@")
-	if i < 0 {
+	before, after, found := strings.Cut(arg, "@")
+	if !found {
 		base.Fatalf("go: -%s=%s: need path@version", flag, arg)
 	}
-	path, version = strings.TrimSpace(arg[:i]), strings.TrimSpace(arg[i+1:])
+	path, version = strings.TrimSpace(before), strings.TrimSpace(after)
 	if err := module.CheckImportPath(path); err != nil {
 		base.Fatalf("go: -%s=%s: invalid path: %v", flag, arg, err)
 	}
@@ -293,10 +293,11 @@ func parsePath(flag, arg string) (path string) {
 // parsePathVersionOptional parses path[@version], using adj to
 // describe any errors.
 func parsePathVersionOptional(adj, arg string, allowDirPath bool) (path, version string, err error) {
-	if i := strings.Index(arg, "@"); i < 0 {
+	before, after, found := strings.Cut(arg, "@")
+	if !found {
 		path = arg
 	} else {
-		path, version = strings.TrimSpace(arg[:i]), strings.TrimSpace(arg[i+1:])
+		path, version = strings.TrimSpace(before), strings.TrimSpace(after)
 	}
 	if err := module.CheckImportPath(path); err != nil {
 		if !allowDirPath || !modfile.IsDirectoryPath(path) {
@@ -324,12 +325,12 @@ func parseVersionInterval(arg string) (modfile.VersionInterval, error) {
 		return modfile.VersionInterval{}, fmt.Errorf("invalid version interval: %q", arg)
 	}
 	s := arg[1 : len(arg)-1]
-	i := strings.Index(s, ",")
-	if i < 0 {
+	before, after, found := strings.Cut(s, ",")
+	if !found {
 		return modfile.VersionInterval{}, fmt.Errorf("invalid version interval: %q", arg)
 	}
-	low := strings.TrimSpace(s[:i])
-	high := strings.TrimSpace(s[i+1:])
+	low := strings.TrimSpace(before)
+	high := strings.TrimSpace(after)
 	if !allowedVersionArg(low) || !allowedVersionArg(high) {
 		return modfile.VersionInterval{}, fmt.Errorf("invalid version interval: %q", arg)
 	}
@@ -387,11 +388,11 @@ func flagDropExclude(arg string) {
 
 // flagReplace implements the -replace flag.
 func flagReplace(arg string) {
-	var i int
-	if i = strings.Index(arg, "="); i < 0 {
+	before, after, found := strings.Cut(arg, "=")
+	if !found {
 		base.Fatalf("go: -replace=%s: need old[@v]=new[@w] (missing =)", arg)
 	}
-	old, new := strings.TrimSpace(arg[:i]), strings.TrimSpace(arg[i+1:])
+	old, new := strings.TrimSpace(before), strings.TrimSpace(after)
 	if strings.HasPrefix(new, ">") {
 		base.Fatalf("go: -replace=%s: separator between old and new is =, not =>", arg)
 	}
diff --git a/src/cmd/go/internal/modconv/dep.go b/src/cmd/go/internal/modconv/dep.go
index 2e673c3ab9..9bea761b49 100644
--- a/src/cmd/go/internal/modconv/dep.go
+++ b/src/cmd/go/internal/modconv/dep.go
@@ -44,12 +44,12 @@ func ParseGopkgLock(file string, data []byte) (*modfile.File, error) {
 		if r == nil {
 			continue
 		}
-		i := strings.Index(line, "=")
-		if i < 0 {
+		before, after, found := strings.Cut(line, "=")
+		if !found {
 			continue
 		}
-		key := strings.TrimSpace(line[:i])
-		val := strings.TrimSpace(line[i+1:])
+		key := strings.TrimSpace(before)
+		val := strings.TrimSpace(after)
 		if len(val) >= 2 && val[0] == '"' && val[len(val)-1] == '"' {
 			q, err := strconv.Unquote(val) // Go unquoting, but close enough for now
 			if err != nil {
diff --git a/src/cmd/go/internal/modfetch/codehost/vcs.go b/src/cmd/go/internal/modfetch/codehost/vcs.go
index 99be8646a4..300a23c6ac 100644
--- a/src/cmd/go/internal/modfetch/codehost/vcs.go
+++ b/src/cmd/go/internal/modfetch/codehost/vcs.go
@@ -539,12 +539,12 @@ func bzrParseStat(rev, out string) (*RevInfo, error) {
 		if line[0] == '-' {
 			continue
 		}
-		i := strings.Index(line, ":")
-		if i < 0 {
+		before, after, found := strings.Cut(line, ":")
+		if !found {
 			// End of header, start of commit message.
 			break
 		}
-		key, val := line[:i], strings.TrimSpace(line[i+1:])
+		key, val := before, strings.TrimSpace(after)
 		switch key {
 		case "revno":
 			if j := strings.Index(val, " "); j >= 0 {
diff --git a/src/cmd/go/internal/modget/query.go b/src/cmd/go/internal/modget/query.go
index 8fffb3354c..d18770e889 100644
--- a/src/cmd/go/internal/modget/query.go
+++ b/src/cmd/go/internal/modget/query.go
@@ -138,13 +138,9 @@ func errSet(err error) pathSet { return pathSet{err: err} }
 // newQuery returns a new query parsed from the raw argument,
 // which must be either path or path@version.
 func newQuery(raw string) (*query, error) {
-	pattern := raw
-	rawVers := ""
-	if i := strings.Index(raw, "@"); i >= 0 {
-		pattern, rawVers = raw[:i], raw[i+1:]
-		if strings.Contains(rawVers, "@") || rawVers == "" {
-			return nil, fmt.Errorf("invalid module version syntax %q", raw)
-		}
+	pattern, rawVers, found := strings.Cut(raw, "@")
+	if found && (strings.Contains(rawVers, "@") || rawVers == "") {
+		return nil, fmt.Errorf("invalid module version syntax %q", raw)
 	}
 
 	// If no version suffix is specified, assume @upgrade.
diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index f5e16e2a92..14ba83c9c9 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -89,8 +89,8 @@ func ModuleInfo(ctx context.Context, path string) *modinfo.ModulePublic {
 		return nil
 	}
 
-	if i := strings.Index(path, "@"); i >= 0 {
-		m := module.Version{Path: path[:i], Version: path[i+1:]}
+	if path, vers, found := strings.Cut(path, "@"); found {
+		m := module.Version{Path: path, Version: vers}
 		return moduleInfo(ctx, nil, m, 0, nil)
 	}
 
diff --git a/src/cmd/go/internal/modload/list.go b/src/cmd/go/internal/modload/list.go
index 6586309291..f77901fa21 100644
--- a/src/cmd/go/internal/modload/list.go
+++ b/src/cmd/go/internal/modload/list.go
@@ -140,9 +140,7 @@ func listModules(ctx context.Context, rs *Requirements, args []string, mode List
 			}
 			continue
 		}
-		if i := strings.Index(arg, "@"); i >= 0 {
-			path := arg[:i]
-			vers := arg[i+1:]
+		if path, vers, found := strings.Cut(arg, "@"); found {
 			if vers == "upgrade" || vers == "patch" {
 				if _, ok := rs.rootSelected(path); !ok || rs.pruning == unpruned {
 					needFullGraph = true
@@ -168,10 +166,7 @@ func listModules(ctx context.Context, rs *Requirements, args []string, mode List
 
 	matchedModule := map[module.Version]bool{}
 	for _, arg := range args {
-		if i := strings.Index(arg, "@"); i >= 0 {
-			path := arg[:i]
-			vers := arg[i+1:]
-
+		if path, vers, found := strings.Cut(arg, "@"); found {
 			var current string
 			if mg == nil {
 				current, _ = rs.rootSelected(path)
diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index 2b59763211..dac13e9a4b 100644
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -1507,15 +1507,13 @@ func computeTestInputsID(a *work.Action, testlog []byte) (cache.ActionID, error)
 			continue
 		}
 		s := string(line)
-		i := strings.Index(s, " ")
-		if i < 0 {
+		op, name, found := strings.Cut(s, " ")
+		if !found {
 			if cache.DebugTest {
 				fmt.Fprintf(os.Stderr, "testcache: %s: input list malformed (%q)\n", a.Package.ImportPath, line)
 			}
 			return cache.ActionID{}, errBadTestInputs
 		}
-		op := s[:i]
-		name := s[i+1:]
 		switch op {
 		default:
 			if cache.DebugTest {
diff --git a/src/cmd/go/internal/vcs/vcs.go b/src/cmd/go/internal/vcs/vcs.go
index baa0876742..d2004579c4 100644
--- a/src/cmd/go/internal/vcs/vcs.go
+++ b/src/cmd/go/internal/vcs/vcs.go
@@ -880,11 +880,11 @@ func parseGOVCS(s string) (govcsConfig, error) {
 		if item == "" {
 			return nil, fmt.Errorf("empty entry in GOVCS")
 		}
-		i := strings.Index(item, ":")
-		if i < 0 {
+		pattern, list, found := strings.Cut(item, ":")
+		if !found {
 			return nil, fmt.Errorf("malformed entry in GOVCS (missing colon): %q", item)
 		}
-		pattern, list := strings.TrimSpace(item[:i]), strings.TrimSpace(item[i+1:])
+		pattern, list = strings.TrimSpace(pattern), strings.TrimSpace(list)
 		if pattern == "" {
 			return nil, fmt.Errorf("empty pattern in GOVCS: %q", item)
 		}
diff --git a/src/cmd/go/internal/work/gccgo.go b/src/cmd/go/internal/work/gccgo.go
index d37b8df07b..a65c61ffd5 100644
--- a/src/cmd/go/internal/work/gccgo.go
+++ b/src/cmd/go/internal/work/gccgo.go
@@ -157,10 +157,7 @@ func buildImportcfgSymlinks(b *Builder, root string, importcfg []byte) error {
 		} else {
 			verb, args = line[:i], strings.TrimSpace(line[i+1:])
 		}
-		var before, after string
-		if i := strings.Index(args, "="); i >= 0 {
-			before, after = args[:i], args[i+1:]
-		}
+		before, after, _ := strings.Cut(args, "=")
 		switch verb {
 		default:
 			base.Fatalf("importcfg:%d: unknown directive %q", lineNum, verb)
diff --git a/src/cmd/go/internal/workcmd/edit.go b/src/cmd/go/internal/workcmd/edit.go
index a0b96cd730..8d1d38318b 100644
--- a/src/cmd/go/internal/workcmd/edit.go
+++ b/src/cmd/go/internal/workcmd/edit.go
@@ -219,10 +219,11 @@ func allowedVersionArg(arg string) bool {
 // parsePathVersionOptional parses path[@version], using adj to
 // describe any errors.
 func parsePathVersionOptional(adj, arg string, allowDirPath bool) (path, version string, err error) {
-	if i := strings.Index(arg, "@"); i < 0 {
+	before, after, found := strings.Cut(arg, "@")
+	if !found {
 		path = arg
 	} else {
-		path, version = strings.TrimSpace(arg[:i]), strings.TrimSpace(arg[i+1:])
+		path, version = strings.TrimSpace(before), strings.TrimSpace(after)
 	}
 	if err := module.CheckImportPath(path); err != nil {
 		if !allowDirPath || !modfile.IsDirectoryPath(path) {
@@ -237,11 +238,11 @@ func parsePathVersionOptional(adj, arg string, allowDirPath bool) (path, version
 
 // flagEditworkReplace implements the -replace flag.
 func flagEditworkReplace(arg string) {
-	var i int
-	if i = strings.Index(arg, "="); i < 0 {
+	before, after, found := strings.Cut(arg, "=")
+	if !found {
 		base.Fatalf("go: -replace=%s: need old[@v]=new[@w] (missing =)", arg)
 	}
-	old, new := strings.TrimSpace(arg[:i]), strings.TrimSpace(arg[i+1:])
+	old, new := strings.TrimSpace(before), strings.TrimSpace(after)
 	if strings.HasPrefix(new, ">") {
 		base.Fatalf("go: -replace=%s: separator between old and new is =, not =>", arg)
 	}