all: minor wins with strings.Cut and utf8.AppendRune

Both of these APIs were added in Go 1.18.
Note that utf8.AppendRune already has a fast path for ASCII.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Icab92b3f194e8395eaafaeb3a35398e3258ced11
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/557324
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Paul Jolly <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

cmd/cue/cmd/common.go

@@ -77,7 +77,7 @@ func getLang() language.Tag {
 	if loc == "" {
 		loc = os.Getenv("LANG")
 	}
-	loc = strings.Split(loc, ".")[0]
+	loc, _, _ = strings.Cut(loc, ".")
 	return language.Make(loc)
 }
 

cue/literal/quote.go

@@ -223,7 +223,6 @@ func (f Form) appendEscaped(buf []byte, s string) []byte {
 }
 
 func (f *Form) appendEscapedRune(buf []byte, r rune) []byte {
-	var runeTmp [utf8.UTFMax]byte
 	if (!f.multiline && r == rune(f.quote)) || r == '\\' { // always backslashed
 		buf = f.appendEscape(buf)
 		buf = append(buf, byte(r))
@@ -235,8 +234,7 @@ func (f *Form) appendEscapedRune(buf []byte, r rune) []byte {
 			return buf
 		}
 	} else if strconv.IsPrint(r) || f.graphicOnly && isInGraphicList(r) {
-		n := utf8.EncodeRune(runeTmp[:], r)
-		buf = append(buf, runeTmp[:n]...)
+		buf = utf8.AppendRune(buf, r)
 		return buf
 	}
 	buf = f.appendEscape(buf)

cue/literal/string.go

@@ -154,7 +154,6 @@ func (q QuoteInfo) Unquote(s string) (string, error) {
 		}
 	}
 
-	var runeTmp [utf8.UTFMax]byte
 	buf := make([]byte, 0, 3*len(s)/2) // Try to avoid more allocations.
 	stripNL := false
 	wasEscapedNewline := false
@@ -220,11 +219,10 @@ func (q QuoteInfo) Unquote(s string) (string, error) {
 		}
 		stripNL = false
 		wasEscapedNewline = false
-		if c < utf8.RuneSelf || !multibyte {
+		if !multibyte {
 			buf = append(buf, byte(c))
 		} else {
-			n := utf8.EncodeRune(runeTmp[:], c)
-			buf = append(buf, runeTmp[:n]...)
+			buf = utf8.AppendRune(buf, c)
 		}
 	}
 	// allow unmatched quotes if already checked.

internal/value/value.go

@@ -51,8 +51,7 @@ func Make(ctx *adt.OpContext, v adt.Value) cue.Value {
 
 // UnifyBuiltin returns the given Value unified with the given builtin template.
 func UnifyBuiltin(v cue.Value, kind string) cue.Value {
-	p := strings.Split(kind, ".")
-	pkg, name := p[0], p[1]
+	pkg, name, _ := strings.Cut(kind, ".")
 	s := runtime.SharedRuntime.LoadImport(pkg)
 	if s == nil {
 		return v

pkg/tool/os/env.go

@@ -98,11 +98,7 @@ func (c *environCmd) Run(ctx *task.Context) (res interface{}, err error) {
 	update := map[string]interface{}{}
 
 	for _, kv := range os.Environ() {
-		a := strings.SplitN(kv, "=", 2)
-
-		name := a[0]
-		str := a[1]
-
+		name, str, _ := strings.Cut(kv, "=")
 		if v := ctx.Obj.Lookup(name); v.Exists() {
 			update[name], err = fromString(name, str, v)
 			if err != nil {