Replace manual utf8.DecodeRune with range string loops

ui/buffer/rope.go

@@ -36,17 +36,12 @@ func (b *RopeBuffer) LineColToPos(line, col int) int {
 
 		l.EachLeaf(func(n *ropes.Node) bool {
 			data := n.Value() // Reference; not a copy.
-			var i int
-			for i < len(data) {
-				if col == 0 || data[i] == '\n' {
+			for _, r := range string(data) {
+				if col == 0 || r == '\n' {
 					return true // Found the position of the column
 				}
 				pos++
 				col--
-
-				// Respect Utf-8 codepoint boundaries
-				_, size := utf8.DecodeRune(data[i:])
-				i += size
 			}
 			return false // Have not gotten to the appropriate position, yet
 		})
@@ -68,11 +63,11 @@ func (b *RopeBuffer) Line(line int) []byte {
 	var isCRLF bool // true if the last byte was '\r'
 	l.EachLeaf(func(n *ropes.Node) bool {
 		data := n.Value() // Reference; not a copy.
-		var i int
-		for i < len(data) {
-			if data[i] == '\r' {
+		for i, r := range string(data) {
+			if r == '\r' {
 				isCRLF = true
-			} else if data[i] == '\n' {
+			} else if r == '\n' {
+				bytes += i // Add bytes before i
 				if isCRLF {
 					bytes += 2 // Add the CRLF bytes
 				} else {
@@ -82,12 +77,8 @@ func (b *RopeBuffer) Line(line int) []byte {
 			} else {
 				isCRLF = false
 			}
-
-			// Respect Utf-8 codepoint boundaries
-			_, size := utf8.DecodeRune(data[i:])
-			bytes += size
-			i += size
 		}
+		bytes += len(data)
 		return false // Have not read the whole line, yet
 	})
 
@@ -198,27 +189,14 @@ func (b *RopeBuffer) RunesInLineWithDelim(line int) int {
 	_, r := b.rope.SplitAt(linePos)
 	l, _ := r.SplitAt(ropeLen - linePos)
 
-	var isCRLF bool
 	l.EachLeaf(func(n *ropes.Node) bool {
 		data := n.Value() // Reference; not a copy.
-		var i int
-		for i < len(data) {
+		for _, r := range string(data) {
 			count++ // Before: we count the line delimiter
-			if data[i] == '\r' {
-				isCRLF = true
-			} else if data[i] == '\n' {
+			if r == '\n' {
 				return true // Read (past-tense) the whole line
-			} else {
-				if isCRLF {
-					isCRLF = false
-					count++ // Add the '\r' we previously thought was part of the delim.
 			}
 		}
-
-			// Respect Utf-8 codepoint boundaries
-			_, size := utf8.DecodeRune(data[i:])
-			i += size
-		}
 		return false // Have not read the whole line, yet
 	})
 
@@ -244,11 +222,10 @@ func (b *RopeBuffer) RunesInLine(line int) int {
 	var isCRLF bool
 	l.EachLeaf(func(n *ropes.Node) bool {
 		data := n.Value() // Reference; not a copy.
-		var i int
-		for i < len(data) {
-			if data[i] == '\r' {
+		for _, r := range string(data) {
+			if r == '\r' {
 				isCRLF = true
-			} else if data[i] == '\n' {
+			} else if r == '\n' {
 				return true // Read (past-tense) the whole line
 			} else {
 				if isCRLF {
@@ -257,10 +234,6 @@ func (b *RopeBuffer) RunesInLine(line int) int {
 				}
 			}
 			count++
-
-			// Respect Utf-8 codepoint boundaries
-			_, size := utf8.DecodeRune(data[i:])
-			i += size
 		}
 		return false // Have not read the whole line, yet
 	})

ui/drawfunctions.go

@@ -1,9 +1,8 @@
 package ui
 
 import (
-	"unicode/utf8"
-
 	"github.com/gdamore/tcell/v2"
+	"github.com/mattn/go-runewidth"
 )
 
 // DrawRect renders a filled box at `x` and `y`, of size `width` and `height`.
@@ -16,22 +15,20 @@ func DrawRect(s tcell.Screen, x, y, width, height int, char rune, style tcell.St
 	}
 }
 
-// DrawStr will render each character of a string at `x` and `y`.
-func DrawStr(s tcell.Screen, x, y int, str string, style tcell.Style) {
+// DrawStr will render each character of a string at `x` and `y`. Returned is
+// the number of columns that were drawn to the screen.
+func DrawStr(s tcell.Screen, x, y int, str string, style tcell.Style) int {
 	var col int
-	bytes := []byte(str)
-	var i int
-	for i < len(bytes) {
-		r, size := utf8.DecodeRune(bytes[i:])
+	for _, r := range str {
 		if r == '\n' {
 			col = 0
 			y++
 		} else {
 			s.SetContent(x+col, y, r, nil, style)
 		}
-		i += size
-		col++
+		col += runewidth.RuneWidth(r)
 	}
+	return col
 }
 
 // DrawQuickCharStr renders a string very similar to how DrawStr works, but stylizes the
@@ -41,20 +38,17 @@ func DrawQuickCharStr(s tcell.Screen, x, y int, str string, quickCharIdx int, st
 	var col int
 	var runeIdx int
 
-	bytes := []byte(str)
-	for i := 0; i < len(bytes); runeIdx++ { // i is a byte index
-		r, size := utf8.DecodeRune(bytes[i:])
-
+	for _, r := range str {
 		sty := style
 		if runeIdx == quickCharIdx {
 			sty = style.Underline(true)
 		}
 		s.SetContent(x+col, y, r, nil, sty)
 
-		i += size
-		col++
+		runeIdx++
+		col += runewidth.RuneWidth(r)
 	}
-	return col // TODO: use mattn/runewidth
+	return col
 }
 
 // DrawRectOutline draws only the outline of a rectangle, using `ul`, `ur`, `bl`, and `br`

ui/textedit.go

@@ -476,7 +476,6 @@ func (t *TextEdit) Draw(s tcell.Screen) {
 
 				col += runewidth.RuneWidth(r)
 
-				// Understanding the tab simulation is unnecessary; just know that it works.
 				byteIdx += size
 				runeIdx++
 			}