all: start making more use of strings.Cut

Possibly the most underrated modern strings API.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Ifb803704773b19cac700b56d8ed4fd16c5ed6a55
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1210874
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>

Author: mvdan

cmd/cue/cmd/get_go.go

@@ -1477,9 +1477,7 @@ func getName(name string, tag string) string {
 	tags := reflect.StructTag(tag)
 	for _, s := range []string{"json", "yaml"} {
 		if tag, ok := tags.Lookup(s); ok {
-			if p := strings.Index(tag, ","); p >= 0 {
-				tag = tag[:p]
-			}
+			tag, _, _ = strings.Cut(tag, ",")
 			if tag != "" {
 				return tag
 			}

cue/decode.go

@@ -559,7 +559,7 @@ func typeFields(t reflect.Type) structFields {
 				if tag == "-" {
 					continue
 				}
-				name, opts := parseTag(tag)
+				name, opts, _ := strings.Cut(tag, ",")
 				if !isValidTag(name) {
 					name = ""
 				}
@@ -584,7 +584,7 @@ func typeFields(t reflect.Type) structFields {
 						tag:       tagged,
 						index:     index,
 						typ:       ft,
-						omitEmpty: opts.Contains("omitempty"),
+						omitEmpty: tagOptions(opts).Contains("omitempty"),
 					}
 					field.nameBytes = []byte(field.name)
 					field.equalFold = foldFunc(field.nameBytes)
@@ -698,15 +698,6 @@ func cachedTypeFields(t reflect.Type) structFields {
 // tag, or the empty string. It does not include the leading comma.
 type tagOptions string
 
-// parseTag splits a struct field's json tag into its name and
-// comma-separated options.
-func parseTag(tag string) (string, tagOptions) {
-	if idx := strings.Index(tag, ","); idx != -1 {
-		return tag[:idx], tagOptions(tag[idx+1:])
-	}
-	return tag, tagOptions("")
-}
-
 // Contains reports whether a comma-separated list of options
 // contains a particular substr flag. substr must be surrounded by a
 // string boundary or commas.
@@ -717,10 +708,7 @@ func (o tagOptions) Contains(optionName string) bool {
 	s := string(o)
 	for s != "" {
 		var next string
-		i := strings.Index(s, ",")
-		if i >= 0 {
-			s, next = s[:i], s[i+1:]
-		}
+		s, next, _ = strings.Cut(s, ",")
 		if s == optionName {
 			return true
 		}

cue/load/tags.go

@@ -291,19 +291,19 @@ func findTags(b *build.Instance) (tags []*tag, errs errors.Error) {
 func (tg *tagger) injectTags(tags []string) errors.Error {
 	// Parses command line args
 	for _, s := range tags {
-		p := strings.Index(s, "=")
+		name, val, ok := strings.Cut(s, "=")
 		found := tg.usedTags[s]
-		if p > 0 { // key-value
+		if ok { // key-value
 			for _, t := range tg.tags {
-				if t.key == s[:p] {
+				if t.key == name {
 					found = true
-					if err := t.inject(s[p+1:], tg); err != nil {
+					if err := t.inject(val, tg); err != nil {
 						return err
 					}
 				}
 			}
 			if !found {
-				return errors.Newf(token.NoPos, "no tag for %q", s[:p])
+				return errors.Newf(token.NoPos, "no tag for %q", name)
 			}
 		} else { // shorthand
 			for _, t := range tg.tags {

mod/module/module.go

@@ -254,15 +254,8 @@ func Sort(list []Version) {
 		// To help go.sum formatting, allow version/file.
 		// Compare semver prefix by semver rules,
 		// file by string order.
-		va := a.version
-		vb := b.version
-		var fa, fb string
-		if k := strings.Index(va, "/"); k >= 0 {
-			va, fa = va[:k], va[k:]
-		}
-		if k := strings.Index(vb, "/"); k >= 0 {
-			vb, fb = vb[:k], vb[k:]
-		}
+		va, fa, _ := strings.Cut(a.version, "/")
+		vb, fb, _ := strings.Cut(b.version, "/")
 		if c := semver.Compare(va, vb); c != 0 {
 			return c
 		}

mod/module/path.go

@@ -114,20 +114,17 @@ func CheckPathWithoutVersion(basePath string) (err error) {
 	if err := checkPath(basePath, modulePath); err != nil {
 		return err
 	}
-	i := strings.Index(basePath, "/")
-	if i < 0 {
-		i = len(basePath)
-	}
-	if i == 0 {
+	firstPath, _, _ := strings.Cut(basePath, "/")
+	if firstPath == "" {
 		return fmt.Errorf("leading slash")
 	}
-	if !strings.Contains(basePath[:i], ".") {
+	if !strings.Contains(firstPath, ".") {
 		return fmt.Errorf("missing dot in first path element")
 	}
 	if basePath[0] == '-' {
 		return fmt.Errorf("leading dash in first path element")
 	}
-	for _, r := range basePath[:i] {
+	for _, r := range firstPath {
 		if !firstPathOK(r) {
 			return fmt.Errorf("invalid char %q in first path element", r)
 		}
@@ -297,10 +294,7 @@ func checkElem(elem string, kind pathKind) error {
 	}
 	// Windows disallows a bunch of path elements, sadly.
 	// See https://docs.microsoft.com/en-us/windows/desktop/fileio/naming-a-file
-	short := elem
-	if i := strings.Index(short, "."); i >= 0 {
-		short = short[:i]
-	}
+	short, _, _ := strings.Cut(elem, ".")
 	for _, bad := range badWindowsNames {
 		if strings.EqualFold(bad, short) {
 			return fmt.Errorf("%q disallowed as path element component on Windows", short)