Upgraded rivo/uniseg to latest version, switched StringWidth/Truncate to speedier version

.github/workflows/test.yaml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, macos-latest, ubuntu-latest]
-        go: ["1.15", "1.16"]
+        go: ["1.15.x", "1.16.x"]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2

benchmark_test.go

@@ -113,21 +113,19 @@ func benchString1Width(b *testing.B, eastAsianWidth bool, start, stop rune, want
 	return n
 }
 func BenchmarkString1WidthAll(b *testing.B) {
-	benchSink = benchString1Width(b, false, 0, utf8.MaxRune+1, 1295990)
+	benchSink = benchString1Width(b, false, 0, utf8.MaxRune+1, 1298422)
 }
 func BenchmarkString1Width768(b *testing.B) {
 	benchSink = benchString1Width(b, false, 0, 0x300, 702)
 }
 func BenchmarkString1WidthAllEastAsian(b *testing.B) {
-	benchSink = benchString1Width(b, true, 0, utf8.MaxRune+1, 1436664)
+	benchSink = benchString1Width(b, true, 0, utf8.MaxRune+1, 1439014)
 }
 func BenchmarkString1Width768EastAsian(b *testing.B) {
 	benchSink = benchString1Width(b, true, 0, 0x300, 794)
 }
 
-//
 // tables
-//
 func benchTable(b *testing.B, tbl table) int {
 	n := 0
 	for i := 0; i < b.N; i++ {

go.mod

@@ -1,5 +1,5 @@
 module github.com/mattn/go-runewidth
 
-go 1.9
+go 1.16
 
 require github.com/rivo/uniseg v0.2.0

runewidth.go → runewidth_go117.go

@@ -1,7 +1,11 @@
+//go:build !go1.18
+// +build !go1.18
+
 package runewidth
 
 import (
 	"os"
+	"strings"
 
 	"github.com/rivo/uniseg"
 )
@@ -177,11 +181,12 @@ func (c *Condition) StringWidth(s string) (width int) {
 	g := uniseg.NewGraphemes(s)
 	for g.Next() {
 		var chWidth int
-		for _, r := range g.Runes() {
-			chWidth = c.RuneWidth(r)
-			if chWidth > 0 {
-				break // Our best guess at this point is to use the width of the first non-zero-width rune.
+		for index, r := range g.Str() {
+			if index == 0 && inTable(r, emoji) {
+				chWidth = 2 // Not the optimal solution but it will work in most cases.
+				break
 			}
+			chWidth += c.RuneWidth(r)
 		}
 		width += chWidth
 	}
@@ -194,24 +199,63 @@ func (c *Condition) Truncate(s string, w int, tail string) string {
 		return s
 	}
 	w -= c.StringWidth(tail)
+	var width, pos int
+	g := uniseg.NewGraphemes(s)
+	for g.Next() {
+		var chWidth int
+		ch := g.Str()
+		for index, r := range ch {
+			if index == 0 && inTable(r, emoji) {
+				chWidth = 2 // Not the optimal solution but it will work in most cases.
+				break
+			}
+			chWidth += c.RuneWidth(r)
+		}
+		if width+chWidth > w {
+			break
+		}
+		width += chWidth
+		pos += len(ch)
+	}
+	return s[:pos] + tail
+}
+
+// TruncateLeft cuts w cells from the beginning of the `s`.
+func (c *Condition) TruncateLeft(s string, w int, prefix string) string {
+	if c.StringWidth(s) <= w {
+		return prefix
+	}
+
 	var width int
 	pos := len(s)
+
 	g := uniseg.NewGraphemes(s)
 	for g.Next() {
 		var chWidth int
-		for _, r := range g.Runes() {
-			chWidth = c.RuneWidth(r)
-			if chWidth > 0 {
-				break // See StringWidth() for details.
+		ch := g.Str()
+		for index, r := range ch {
+			if index == 0 && inTable(r, emoji) {
+				chWidth = 2 // Not the optimal solution but it will work in most cases.
+				break
 			}
+			chWidth += c.RuneWidth(r)
 		}
+
 		if width+chWidth > w {
-			pos, _ = g.Positions()
+			if width < w {
+				_, pos = g.Positions()
+				prefix += strings.Repeat(" ", width+chWidth-w)
+			} else {
+				pos, _ = g.Positions()
+			}
+
 			break
 		}
+
 		width += chWidth
 	}
-	return s[:pos] + tail
+
+	return prefix + s[pos:]
 }
 
 // Wrap return string wrapped with w cells
@@ -291,6 +335,11 @@ func Truncate(s string, w int, tail string) string {
 	return DefaultCondition.Truncate(s, w, tail)
 }
 
+// TruncateLeft cuts w cells from the beginning of the `s`.
+func TruncateLeft(s string, w int, prefix string) string {
+	return DefaultCondition.TruncateLeft(s, w, prefix)
+}
+
 // Wrap return string wrapped with w cells
 func Wrap(s string, w int) string {
 	return DefaultCondition.Wrap(s, w)