Optimize replaceAll (#931)

CHANGELOG.md

@@ -9,6 +9,7 @@ Change Log
 
 - Adjust the text baseline to draw characters vertically center in lines.
 - Adjust the invisible characters position in the vertical text orientation.
+- Optimize the performance of “Replace All” with a large number of matches.
 - Duplicate lines more intelligently.
 - Use mirrored pilcrow sign “⁋” for an invisible line ending symbol in RTL mode.
 - Improve drawing performance.

CotEditor/Sources/TextFind.swift

@@ -338,16 +338,16 @@ final class TextFind {
                 length = scopeRange.length
             } else {
                 // build replacementString
-                var replacedString = (self.string as NSString).substring(with: scopeRange) as NSString
+                let replacedString = NSMutableString(string: (self.string as NSString).substring(with: scopeRange))
                 for item in items.reversed() {
                     block(.replacementProgress, &ioStop)
                     if ioStop { return }
                     
                     // -> Do not convert to Range<Index>. It can fail when the range is smaller than String.Character.
                     let substringRange = item.range.shifted(offset: -scopeRange.location)
-                    replacedString = replacedString.replacingCharacters(in: substringRange, with: item.string) as NSString
+                    replacedString.replaceCharacters(in: substringRange, with: item.string)
                 }
-                replacementItems.append(ReplacementItem(string: replacedString as String, range: scopeRange))
+                replacementItems.append(ReplacementItem(string: replacedString.copy() as! String, range: scopeRange))
                 length = replacedString.length
             }