readline: move charLengthLeft() and charLengthAt()

This moves the charLengthLeft() and charLengthAt() into the internal
readline file. This allows sharing the functions internally with
other code.
PR-URL: #31112
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: BridgeAR

lib/internal/readline/utils.js

@@ -36,6 +36,29 @@ CSI.kClearToLineEnd = CSI`0K`;
 CSI.kClearLine=CSI`2K`;
 CSI.kClearScreenDown=CSI`0J`;
 
+// TODO(BridgeAR): Treat combined characters as single character, i.e,
+// 'a\u0301' and '\u0301a' (both have the same visual output).
+// Check Canonical_Combining_Class in
+// http://userguide.icu-project.org/strings/properties
+functioncharLengthLeft(str,i){
+if(i<=0)
+return0;
+if((i>1&&str.codePointAt(i-2)>=kUTF16SurrogateThreshold)||
+str.codePointAt(i-1)>=kUTF16SurrogateThreshold){
+return2;
+}
+return1;
+}
+
+functioncharLengthAt(str,i){
+if(str.length<=i){
+// Pretend to move to the right. This is necessary to autocomplete while
+// moving to the right.
+return1;
+}
+returnstr.codePointAt(i)>=kUTF16SurrogateThreshold ? 2 : 1;
+}
+
 if(internalBinding('config').hasIntl){
 consticu=internalBinding('icu');
 // icu.getStringWidth(string, ambiguousAsFullWidth, expandEmojiSequence)
@@ -452,6 +475,8 @@ function commonPrefix(strings) {
 }
 
 module.exports={
+ charLengthAt,
+ charLengthLeft,
  commonPrefix,
  emitKeys,
  getStringWidth,

lib/readline.js

@@ -49,6 +49,8 @@ const { validateString } = require('internal/validators');
 const{ inspect }=require('internal/util/inspect');
 constEventEmitter=require('events');
 const{
+ charLengthAt,
+ charLengthLeft,
  commonPrefix,
 CSI,
  emitKeys,
@@ -591,25 +593,6 @@ Interface.prototype._wordRight = function() {
 }
 };
 
-functioncharLengthLeft(str,i){
-if(i<=0)
-return0;
-if((i>1&&str.codePointAt(i-2)>=kUTF16SurrogateThreshold)||
-str.codePointAt(i-1)>=kUTF16SurrogateThreshold){
-return2;
-}
-return1;
-}
-
-functioncharLengthAt(str,i){
-if(str.length<=i){
-// Pretend to move to the right. This is necessary to autocomplete while
-// moving to the right.
-return1;
-}
-returnstr.codePointAt(i)>=kUTF16SurrogateThreshold ? 2 : 1;
-}
-
 Interface.prototype._deleteLeft=function(){
 if(this.cursor>0&&this.line.length>0){
 // The number of UTF-16 units comprising the character to the left