highlighter: Change the parsing approach to significantly improve performance

internal/buffer/buffer.go

@@ -148,11 +148,7 @@ func (b *SharedBuffer) MarkModified(start, end int) {
 	end = util.Clamp(end, 0, len(b.lines)-1)
 
 	if b.Settings["syntax"].(bool) && b.SyntaxDef != nil {
-		l := -1
-		for i := start; i <= end; i++ {
-			l = util.Max(b.Highlighter.ReHighlightStates(b, i), l)
-		}
-		b.Highlighter.HighlightMatches(b, start, l)
+		b.Highlighter.Highlight(b, start, end)
 	}
 
 	for i := start; i <= end; i++ {
@@ -961,8 +957,7 @@ func (b *Buffer) UpdateRules() {
 		b.Highlighter = highlight.NewHighlighter(b.SyntaxDef)
 		if b.Settings["syntax"].(bool) {
 			go func() {
-				b.Highlighter.HighlightStates(b)
-				b.Highlighter.HighlightMatches(b, 0, b.End().Y)
+				b.Highlighter.Highlight(b, 0, b.End().Y)
 				screen.Redraw()
 			}()
 		}

internal/util/util.go

@@ -133,6 +133,16 @@ func SliceStartStr(str string, index int) string {
 	return str[:totalSize]
 }
 
+// SliceStartEnd combines SliceStart and SliceEnd into one
+func SliceStartEnd(slc []byte, start int, end int) []byte {
+	return SliceEnd(SliceStart(slc, end), start)
+}
+
+// SliceStartEndStr is the same as SliceStartEnd but for strings
+func SliceStartEndStr(str string, start int, end int) string {
+	return SliceEndStr(SliceStartStr(str, end), start)
+}
+
 // SliceVisualEnd will take a byte slice and slice off the start
 // up to a given visual index. If the index is in the middle of a
 // rune the number of visual columns into the rune will be returned