swift 6 cannot open correctly a windowsCP1252 file in linux (worked on swift 5 and macos)

[Dracks]

Description

Opening a file that is an export of transactions from an spanish bank (Caixa enginyers) which is an xls (html+latin1252) it gives a bad format using swift 6 compiler in linux. In mac-os or using swift 5.10 compiler works fine

Reproduction

Download the sample file:
https://github.com/Dracks/mr-scrooge/blob/mr-scrooge-3.0.0/src/swift-server-tests/test_files/MovimientosCuenta.xls

	guard let fileData = FileManager.default.contents(atPath: filePath)
				else {
					return
				}
				guard let fileString = String(data: fileData, encoding: .windowsCP1252)
				else {
					return
				}

Expected behavior

get's the contents of the file in fileString variable. (Now the second ward execute the else case)

Environment

Swift version 6.0.2 (swift-6.0.2-RELEASE)
Target: x86_64-unknown-linux-gnu

Additional information

The link is a sample file exported from my bank, and anonymized, that I've got to run tests of my app. But today I expecuted it on my machine using the original file downloaded from the bank account and the same happened.

[TimBudarick]

I can agree with that. We also have this issue, by reading a file from Windows.

We read large TXT files line by line. We do this using a FileHandle. If we use the Swift windowsCP1252 encoding, we do not receive a single line.
However, if we copy the exact same file to a Mac and execute the exact same source code, the file will be read completely and correctly.

This situation exists not only under Linux but also under Windows.

We have implemented the WindowsCP-1252 encoding manually.
This implementation is really not clean, but it works for our purposes.

import Foundation

String.Encoding {
    static let windowsCP1252Map : [UInt8 : String] = [
        0x0: "",  // NULL,
        0x1: "\u{0001}",  // START OF HEADING,
        0x2: "\u{0002}",  // START OF TEXT,
        0x3: "\u{0003}",  // END OF TEXT,
        0x4: "\u{0004}",  // END OF TRANSMISSION,
        0x5: "\u{0005}",  // ENQUIRY,
        0x6: "\u{0006}",  // ACKNOWLEDGE,
        0x7: "\u{0007}",  // BELL,
        0x8: "\u{0008}",  // BACKSPACE,
        0x9: "\u{0009}",  // HORIZONTAL TABULATION,
        0xa: "\u{000A}",  // LINE FEED,
        0xb: "\u{000B}",  // VERTICAL TABULATION,
        0xc: "\u{000C}",  // FORM FEED,
        0xd: "\u{000D}",  // CARRIAGE RETURN,
        0xe: "\u{000E}",  // SHIFT OUT,
        0xf: "\u{000F}",  // SHIFT IN,
        0x10: "\u{0010}",  // DATA LINK ESCAPE,
        0x11: "\u{0011}",  // DEVICE CONTROL ONE,
        0x12: "\u{0012}",  // DEVICE CONTROL TWO,
        0x13: "\u{0013}",  // DEVICE CONTROL THREE,
        0x14: "\u{0014}",  // DEVICE CONTROL FOUR,
        0x15: "\u{0015}",  // NEGATIVE ACKNOWLEDGE,
        0x16: "\u{0016}",  // SYNCHRONOUS IDLE,
        0x17: "\u{0017}",  // END OF TRANSMISSION BLOCK,
        0x18: "\u{0018}",  // CANCEL,
        0x19: "\u{0019}",  // END OF MEDIUM,
        0x1a: "\u{001A}",  // SUBSTITUTE,
        0x1b: "\u{001B}",  // ESCAPE,
        0x1c: "\u{001C}",  // FILE SEPARATOR,
        0x1d: "\u{001D}",  // GROUP SEPARATOR,
        0x1e: "\u{001E}",  // RECORD SEPARATOR,
        0x1f: "\u{001F}",  // UNIT SEPARATOR,
        0x20: "\u{0020}",  // SPACE,
        0x21: "\u{0021}",  // EXCLAMATION MARK,
        0x22: "\u{0022}",  // QUOTATION MARK,
        0x23: "\u{0023}",  // NUMBER SIGN,
        0x24: "\u{0024}",  // DOLLAR SIGN,
        0x25: "\u{0025}",  // PERCENT SIGN,
        0x26: "\u{0026}",  // AMPERSAND,
        0x27: "\u{0027}",  // APOSTROPHE,
        0x28: "\u{0028}",  // LEFT PARENTHESIS,
        0x29: "\u{0029}",  // RIGHT PARENTHESIS,
        0x2a: "\u{002A}",  // ASTERISK,
        0x2b: "\u{002B}",  // PLUS SIGN,
        0x2c: "\u{002C}",  // COMMA,
        0x2d: "\u{002D}",  // HYPHEN-MINUS,
        0x2e: "\u{002E}",  // FULL STOP,
        0x2f: "\u{002F}",  // SOLIDUS,
        0x30: "\u{0030}",  // DIGIT ZERO,
        0x31: "\u{0031}",  // DIGIT ONE,
        0x32: "\u{0032}",  // DIGIT TWO,
        0x33: "\u{0033}",  // DIGIT THREE,
        0x34: "\u{0034}",  // DIGIT FOUR,
        0x35: "\u{0035}",  // DIGIT FIVE,
        0x36: "\u{0036}",  // DIGIT SIX,
        0x37: "\u{0037}",  // DIGIT SEVEN,
        0x38: "\u{0038}",  // DIGIT EIGHT,
        0x39: "\u{0039}",  // DIGIT NINE,
        0x3a: "\u{003A}",  // COLON,
        0x3b: "\u{003B}",  // SEMICOLON,
        0x3c: "\u{003C}",  // LESS-THAN SIGN,
        0x3d: "\u{003D}",  // EQUALS SIGN,
        0x3e: "\u{003E}",  // GREATER-THAN SIGN,
        0x3f: "\u{003F}",  // QUESTION MARK,
        0x40: "\u{0040}",  // COMMERCIAL AT,
        0x41: "\u{0041}",  // LATIN CAPITAL LETTER A,
        0x42: "\u{0042}",  // LATIN CAPITAL LETTER B,
        0x43: "\u{0043}",  // LATIN CAPITAL LETTER C,
        0x44: "\u{0044}",  // LATIN CAPITAL LETTER D,
        0x45: "\u{0045}",  // LATIN CAPITAL LETTER E,
        0x46: "\u{0046}",  // LATIN CAPITAL LETTER F,
        0x47: "\u{0047}",  // LATIN CAPITAL LETTER G,
        0x48: "\u{0048}",  // LATIN CAPITAL LETTER H,
        0x49: "\u{0049}",  // LATIN CAPITAL LETTER I,
        0x4a: "\u{004A}",  // LATIN CAPITAL LETTER J,
        0x4b: "\u{004B}",  // LATIN CAPITAL LETTER K,
        0x4c: "\u{004C}",  // LATIN CAPITAL LETTER L,
        0x4d: "\u{004D}",  // LATIN CAPITAL LETTER M,
        0x4e: "\u{004E}",  // LATIN CAPITAL LETTER N,
        0x4f: "\u{004F}",  // LATIN CAPITAL LETTER O,
        0x50: "\u{0050}",  // LATIN CAPITAL LETTER P,
        0x51: "\u{0051}",  // LATIN CAPITAL LETTER Q,
        0x52: "\u{0052}",  // LATIN CAPITAL LETTER R,
        0x53: "\u{0053}",  // LATIN CAPITAL LETTER S,
        0x54: "\u{0054}",  // LATIN CAPITAL LETTER T,
        0x55: "\u{0055}",  // LATIN CAPITAL LETTER U,
        0x56: "\u{0056}",  // LATIN CAPITAL LETTER V,
        0x57: "\u{0057}",  // LATIN CAPITAL LETTER W,
        0x58: "\u{0058}",  // LATIN CAPITAL LETTER X,
        0x59: "\u{0059}",  // LATIN CAPITAL LETTER Y,
        0x5a: "\u{005A}",  // LATIN CAPITAL LETTER Z,
        0x5b: "\u{005B}",  // LEFT SQUARE BRACKET,
        0x5c: "\u{005C}",  // REVERSE SOLIDUS,
        0x5d: "\u{005D}",  // RIGHT SQUARE BRACKET,
        0x5e: "\u{005E}",  // CIRCUMFLEX ACCENT,
        0x5f: "\u{005F}",  // LOW LINE,
        0x60: "\u{0060}",  // GRAVE ACCENT,
        0x61: "\u{0061}",  // LATIN SMALL LETTER A,
        0x62: "\u{0062}",  // LATIN SMALL LETTER B,
        0x63: "\u{0063}",  // LATIN SMALL LETTER C,
        0x64: "\u{0064}",  // LATIN SMALL LETTER D,
        0x65: "\u{0065}",  // LATIN SMALL LETTER E,
        0x66: "\u{0066}",  // LATIN SMALL LETTER F,
        0x67: "\u{0067}",  // LATIN SMALL LETTER G,
        0x68: "\u{0068}",  // LATIN SMALL LETTER H,
        0x69: "\u{0069}",  // LATIN SMALL LETTER I,
        0x6a: "\u{006A}",  // LATIN SMALL LETTER J,
        0x6b: "\u{006B}",  // LATIN SMALL LETTER K,
        0x6c: "\u{006C}",  // LATIN SMALL LETTER L,
        0x6d: "\u{006D}",  // LATIN SMALL LETTER M,
        0x6e: "\u{006E}",  // LATIN SMALL LETTER N,
        0x6f: "\u{006F}",  // LATIN SMALL LETTER O,
        0x70: "\u{0070}",  // LATIN SMALL LETTER P,
        0x71: "\u{0071}",  // LATIN SMALL LETTER Q,
        0x72: "\u{0072}",  // LATIN SMALL LETTER R,
        0x73: "\u{0073}",  // LATIN SMALL LETTER S,
        0x74: "\u{0074}",  // LATIN SMALL LETTER T,
        0x75: "\u{0075}",  // LATIN SMALL LETTER U,
        0x76: "\u{0076}",  // LATIN SMALL LETTER V,
        0x77: "\u{0077}",  // LATIN SMALL LETTER W,
        0x78: "\u{0078}",  // LATIN SMALL LETTER X,
        0x79: "\u{0079}",  // LATIN SMALL LETTER Y,
        0x7a: "\u{007A}",  // LATIN SMALL LETTER Z,
        0x7b: "\u{007B}",  // LEFT CURLY BRACKET,
        0x7c: "\u{007C}",  // VERTICAL LINE,
        0x7d: "\u{007D}",  // RIGHT CURLY BRACKET,
        0x7e: "\u{007E}",  // TILDE,
        0x7f: "\u{007F}",  // DELETE,
        0x80: "\u{20AC}",  // EURO SIGN,
        0x81: "\u{FFFD}",  // UNDEFINED,
        0x82: "\u{201A}",  // SINGLE LOW-9 QUOTATION MARK,
        0x83: "\u{0192}",  // LATIN SMALL LETTER F WITH HOOK,
        0x84: "\u{201E}",  // DOUBLE LOW-9 QUOTATION MARK,
        0x85: "\u{2026}",  // HORIZONTAL ELLIPSIS,
        0x86: "\u{2020}",  // DAGGER,
        0x87: "\u{2021}",  // DOUBLE DAGGER,
        0x88: "\u{02C6}",  // MODIFIER LETTER CIRCUMFLEX ACCENT,
        0x89: "\u{2030}",  // PER MILLE SIGN,
        0x8a: "\u{0160}",  // LATIN CAPITAL LETTER S WITH CARON,
        0x8b: "\u{2039}",  // SINGLE LEFT-POINTING ANGLE QUOTATION MARK,
        0x8c: "\u{0152}",  // LATIN CAPITAL LIGATURE OE,
        0x8d: "\u{FFFD}",  // UNDEFINED,
        0x8e: "\u{017D}",  // LATIN CAPITAL LETTER Z WITH CARON,
        0x8f: "\u{FFFD}",  // UNDEFINED,
        0x90: "\u{FFFD}",  // UNDEFINED,
        0x91: "\u{2018}",  // LEFT SINGLE QUOTATION MARK,
        0x92: "\u{2019}",  // RIGHT SINGLE QUOTATION MARK,
        0x93: "\u{201C}",  // LEFT DOUBLE QUOTATION MARK,
        0x94: "\u{201D}",  // RIGHT DOUBLE QUOTATION MARK,
        0x95: "\u{2022}",  // BULLET,
        0x96: "\u{2013}",  // EN DASH,
        0x97: "\u{2014}",  // EM DASH,
        0x98: "\u{02DC}",  // SMALL TILDE,
        0x99: "\u{2122}",  // TRADE MARK SIGN,
        0x9a: "\u{0161}",  // LATIN SMALL LETTER S WITH CARON,
        0x9b: "\u{203A}",  // SINGLE RIGHT-POINTING ANGLE QUOTATION MARK,
        0x9c: "\u{0153}",  // LATIN SMALL LIGATURE OE,
        0x9d: "\u{FFFD}",  // UNDEFINED,
        0x9e: "\u{017E}",  // LATIN SMALL LETTER Z WITH CARON,
        0x9f: "\u{0178}",  // LATIN CAPITAL LETTER Y WITH DIAERESIS,
        0xa0: "\u{00A0}",  // NO-BREAK SPACE,
        0xa1: "\u{00A1}",  // INVERTED EXCLAMATION MARK,
        0xa2: "\u{00A2}",  // CENT SIGN,
        0xa3: "\u{00A3}",  // POUND SIGN,
        0xa4: "\u{00A4}",  // CURRENCY SIGN,
        0xa5: "\u{00A5}",  // YEN SIGN,
        0xa6: "\u{00A6}",  // BROKEN BAR,
        0xa7: "\u{00A7}",  // SECTION SIGN,
        0xa8: "\u{00A8}",  // DIAERESIS,
        0xa9: "\u{00A9}",  // COPYRIGHT SIGN,
        0xaa: "\u{00AA}",  // FEMININE ORDINAL INDICATOR,
        0xab: "\u{00AB}",  // LEFT-POINTING DOUBLE ANGLE QUOTATION MARK,
        0xac: "\u{00AC}",  // NOT SIGN,
        0xad: "\u{00AD}",  // SOFT HYPHEN,
        0xae: "\u{00AE}",  // REGISTERED SIGN,
        0xaf: "\u{00AF}",  // MACRON,
        0xb0: "\u{00B0}",  // DEGREE SIGN,
        0xb1: "\u{00B1}",  // PLUS-MINUS SIGN,
        0xb2: "\u{00B2}",  // SUPERSCRIPT TWO,
        0xb3: "\u{00B3}",  // SUPERSCRIPT THREE,
        0xb4: "\u{00B4}",  // ACUTE ACCENT,
        0xb5: "\u{00B5}",  // MICRO SIGN,
        0xb6: "\u{00B6}",  // PILCROW SIGN,
        0xb7: "\u{00B7}",  // MIDDLE DOT,
        0xb8: "\u{00B8}",  // CEDILLA,
        0xb9: "\u{00B9}",  // SUPERSCRIPT ONE,
        0xba: "\u{00BA}",  // MASCULINE ORDINAL INDICATOR,
        0xbb: "\u{00BB}",  // RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK,
        0xbc: "\u{00BC}",  // VULGAR FRACTION ONE QUARTER,
        0xbd: "\u{00BD}",  // VULGAR FRACTION ONE HALF,
        0xbe: "\u{00BE}",  // VULGAR FRACTION THREE QUARTERS,
        0xbf: "\u{00BF}",  // INVERTED QUESTION MARK,
        0xc0: "\u{00C0}",  // LATIN CAPITAL LETTER A WITH GRAVE,
        0xc1: "\u{00C1}",  // LATIN CAPITAL LETTER A WITH ACUTE,
        0xc2: "\u{00C2}",  // LATIN CAPITAL LETTER A WITH CIRCUMFLEX,
        0xc3: "\u{00C3}",  // LATIN CAPITAL LETTER A WITH TILDE,
        0xc4: "\u{00C4}",  // LATIN CAPITAL LETTER A WITH DIAERESIS,
        0xc5: "\u{00C5}",  // LATIN CAPITAL LETTER A WITH RING ABOVE,
        0xc6: "\u{00C6}",  // LATIN CAPITAL LETTER AE,
        0xc7: "\u{00C7}",  // LATIN CAPITAL LETTER C WITH CEDILLA,
        0xc8: "\u{00C8}",  // LATIN CAPITAL LETTER E WITH GRAVE,
        0xc9: "\u{00C9}",  // LATIN CAPITAL LETTER E WITH ACUTE,
        0xca: "\u{00CA}",  // LATIN CAPITAL LETTER E WITH CIRCUMFLEX,
        0xcb: "\u{00CB}",  // LATIN CAPITAL LETTER E WITH DIAERESIS,
        0xcc: "\u{00CC}",  // LATIN CAPITAL LETTER I WITH GRAVE,
        0xcd: "\u{00CD}",  // LATIN CAPITAL LETTER I WITH ACUTE,
        0xce: "\u{00CE}",  // LATIN CAPITAL LETTER I WITH CIRCUMFLEX,
        0xcf: "\u{00CF}",  // LATIN CAPITAL LETTER I WITH DIAERESIS,
        0xd0: "\u{00D0}",  // LATIN CAPITAL LETTER ETH,
        0xd1: "\u{00D1}",  // LATIN CAPITAL LETTER N WITH TILDE,
        0xd2: "\u{00D2}",  // LATIN CAPITAL LETTER O WITH GRAVE,
        0xd3: "\u{00D3}",  // LATIN CAPITAL LETTER O WITH ACUTE,
        0xd4: "\u{00D4}",  // LATIN CAPITAL LETTER O WITH CIRCUMFLEX,
        0xd5: "\u{00D5}",  // LATIN CAPITAL LETTER O WITH TILDE,
        0xd6: "\u{00D6}",  // LATIN CAPITAL LETTER O WITH DIAERESIS,
        0xd7: "\u{00D7}",  // MULTIPLICATION SIGN,
        0xd8: "\u{00D8}",  // LATIN CAPITAL LETTER O WITH STROKE,
        0xd9: "\u{00D9}",  // LATIN CAPITAL LETTER U WITH GRAVE,
        0xda: "\u{00DA}",  // LATIN CAPITAL LETTER U WITH ACUTE,
        0xdb: "\u{00DB}",  // LATIN CAPITAL LETTER U WITH CIRCUMFLEX,
        0xdc: "\u{00DC}",  // LATIN CAPITAL LETTER U WITH DIAERESIS,
        0xdd: "\u{00DD}",  // LATIN CAPITAL LETTER Y WITH ACUTE,
        0xde: "\u{00DE}",  // LATIN CAPITAL LETTER THORN,
        0xdf: "\u{00DF}",  // LATIN SMALL LETTER SHARP S,
        0xe0: "\u{00E0}",  // LATIN SMALL LETTER A WITH GRAVE,
        0xe1: "\u{00E1}",  // LATIN SMALL LETTER A WITH ACUTE,
        0xe2: "\u{00E2}",  // LATIN SMALL LETTER A WITH CIRCUMFLEX,
        0xe3: "\u{00E3}",  // LATIN SMALL LETTER A WITH TILDE,
        0xe4: "\u{00E4}",  // LATIN SMALL LETTER A WITH DIAERESIS,
        0xe5: "\u{00E5}",  // LATIN SMALL LETTER A WITH RING ABOVE,
        0xe6: "\u{00E6}",  // LATIN SMALL LETTER AE,
        0xe7: "\u{00E7}",  // LATIN SMALL LETTER C WITH CEDILLA,
        0xe8: "\u{00E8}",  // LATIN SMALL LETTER E WITH GRAVE,
        0xe9: "\u{00E9}",  // LATIN SMALL LETTER E WITH ACUTE,
        0xea: "\u{00EA}",  // LATIN SMALL LETTER E WITH CIRCUMFLEX,
        0xeb: "\u{00EB}",  // LATIN SMALL LETTER E WITH DIAERESIS,
        0xec: "\u{00EC}",  // LATIN SMALL LETTER I WITH GRAVE,
        0xed: "\u{00ED}",  // LATIN SMALL LETTER I WITH ACUTE,
        0xee: "\u{00EE}",  // LATIN SMALL LETTER I WITH CIRCUMFLEX,
        0xef: "\u{00EF}",  // LATIN SMALL LETTER I WITH DIAERESIS,
        0xf0: "\u{00F0}",  // LATIN SMALL LETTER ETH,
        0xf1: "\u{00F1}",  // LATIN SMALL LETTER N WITH TILDE,
        0xf2: "\u{00F2}",  // LATIN SMALL LETTER O WITH GRAVE,
        0xf3: "\u{00F3}",  // LATIN SMALL LETTER O WITH ACUTE,
        0xf4: "\u{00F4}",  // LATIN SMALL LETTER O WITH CIRCUMFLEX,
        0xf5: "\u{00F5}",  // LATIN SMALL LETTER O WITH TILDE,
        0xf6: "\u{00F6}",  // LATIN SMALL LETTER O WITH DIAERESIS,
        0xf7: "\u{00F7}",  // DIVISION SIGN,
        0xf8: "\u{00F8}",  // LATIN SMALL LETTER O WITH STROKE,
        0xf9: "\u{00F9}",  // LATIN SMALL LETTER U WITH GRAVE,
        0xfa: "\u{00FA}",  // LATIN SMALL LETTER U WITH ACUTE,
        0xfb: "\u{00FB}",  // LATIN SMALL LETTER U WITH CIRCUMFLEX,
        0xfc: "\u{00FC}",  // LATIN SMALL LETTER U WITH DIAERESIS,
        0xfd: "\u{00FD}",  // LATIN SMALL LETTER Y WITH ACUTE,
        0xfe: "\u{00FE}",  // LATIN SMALL LETTER THORN,
        0xff: "\u{00FF}",  // LATIN SMALL LETTER Y WITH DIAERESIS
    ]

}

extension String {
    
    /// Converts a `Data` object containing Windows CP-1252 encoded bytes into a `String`.
    ///
    /// - Parameters:
    ///   - data: The `Data` object containing the Windows CP-1252 encoded bytes.
    /// - Returns: A `String` object initialized with the decoded characters from the provided data, or `nil` if an invalid byte is encountered.
    static func fromWindowsCP1252(_ data: Data) -> String? {
        var decodedString = ""
        
        for byte in data {
            if let character = String.Encoding.windowsCP1252Map[byte] {
                decodedString.append(character)
            } else {
                return nil
            }
        }
        
        return decodedString
    }
    
    /// Converts a `String` into a `Data` object using Windows CP-1252 encoding.
    ///
    /// - Returns: A `Data` object containing the Windows CP-1252 encoded bytes of the string, or `nil` if any character in the string cannot be represented in Windows CP-1252.
    func toWindowsCP1252() -> Data? {
        var data = Data()
        
        var map = [String: UInt8]()
        for (key, value) in String.Encoding.windowsCP1252Map {
            map[value] = key
        }
        
        for char in self {
            if let byte = map[String(char)] {
                data.append(byte)
            } else {
                return nil
            }
        }
        
        return data
    }
}

Just for the sake of completeness, we compiled our application with the latest Swift SDK for Windows at the time. (Swift 6.0.1)

[TimBudarick]

You can simply use the Default Swift Encoding mechanism when you running the App on macOS. This can be archived by the following change:

static func fromWindowsCP1252(_ data : Data) -> String? {
      #if os(macOS)
      return String(data: data, encoding: .windowsCP1252)
      #else
      var decodedString = ""
      
      for byte in data {
          if let character = String.Encoding.windowsCP1252Map[byte] {
              decodedString.append(character)
          } else {
              return nil
          }
      }
      
      return decodedString
      #endif
  }

[TimBudarick]

My minimal example indicates that the native WindowsCP1252 encoding has failed. I have tested this under Windows Server 2022.

Swift version 6.0.3 (swift-6.0.3-RELEASE)
Target: x86_64-unknown-windows-msvc

import Foundation

// Define an array of CP1252 encoded bytes representing "Hallo " followed by the Euro sign
let cp1252Bytes: [UInt8] = [72, 97, 108, 108, 111, 32, 0x80]
let cp1252Data = Data(cp1252Bytes)

// Try to decode the data using the native CP1252 encoding provided by the system
if let nativeString = String(data: cp1252Data, encoding: .windowsCP1252) {
    print("Native decoding: \(nativeString)")
} else {
    print("Native decoding failed.")
}

// Mapping for special CP1252 characters that are outside the standard ASCII range
let cp1252Mapping: [UInt8: String] = [
    0x80: "€"  // Euro sign
]

// A function to manually decode CP1252 encoded data
func manualCP1252Decode(data: Data) -> String {
    var result = ""
    for byte in data {
        // Check if the byte is in the standard ASCII range (0x20 to 0x7F)
        if byte >= 0x20 && byte <= 0x7F {
            // The byte value directly corresponds to a Unicode scalar
            let scalar = UnicodeScalar(byte)
            result.append(Character(scalar))
        } else if let mapped = cp1252Mapping[byte] {
            // Use the mapped value for special CP1252 characters
            result.append(mapped)
        } else {
            // For unmapped byte values, use a placeholder character
            result.append("?")
        }
    }
    return result
}

let manualString = manualCP1252Decode(data: cp1252Data)
print("Manual decoding: \(manualString)")

macOS Output:

Native decoding: Hallo €
Manual decoding: Hallo €

Windows Output:

Native decoding failed.
Manual decoding: Hallo €

[stefanspringer1]

There are more problems regarding encoding: The following code prints an empty array. Take out the line break, and it prints the correct result.

let str =
"""
a
b
"""
let data = str.data(using: .isoLatin1) ?? Data()
print(Array(data))

[stefanspringer1]

...Also tested with Swift 6.1 (dev, downloaded today), the problems persist.

[parkera]

The cause of the bug is that when data(using:) dropped from swift-corelibs-foundation into swift-foundation, we lost the ability to decode all of the encodings that only CoreFoundation has built-in converters for. We will need to add an upcall into swift-corelibs-foundation when it is present here.

[parkera]

isoLatin1 is implemented, however. That sounds like a different bug, which we should open a separate issue for.

[parkera]

See swiftlang/swift-corelibs-foundation#5193 which will finish the full resolution of this bug by providing the swift-corelibs-foundation upcall for windowsCP1252 (or other) encodings.