Should multi-line raw strings preserve line encoding?

[DartBot]

This issue was originally filed by [email protected]

---

Running:

main() {
  String s1 = 'foo\r\n';
  String s2 = r'''foo^M
''';
  print(s1.codeUnits);
  print(s2.codeUnits);
}

Will output:
[102, 111, 111, 13, 10]
[102, 111, 111, 10]

Before running, replace ^M by an actual carriage return. In Emacs insert a carriage return with C-q RET
Compiling with dart2js and running with d8 produces the expected output:
[102, 111, 111, 13, 10]
[102, 111, 111, 13, 10]

[mhausner]

That would mean that a raw string can change depending on which platform you save the source code. Save it on Windows and you get \r\n on every line ending. Save the same file on Linux and you'll get a string with \n at the end of every line. That seems less than ideal.

[mhausner]

Gilad, could you clarify whether raw strings have to preserve the platform-specific line ending encoding? The spec does not mention this issue other than stating that source is in UTF-8, which leaves line endings platform-dependent. For raw strings, the spec just says that escape sequences and interpolations are not processed.

Thank you.

[peter-ahe-google]

Would it be possible to get a resolution on this? The VM and dart2js disagrees, so it's hard for Fasta to produce the correct behavior. Currently, we've implemented that CRLF is translated to LF which I agree is the least surprising behavior.

[lrhn]

I have updated the specification in the repository (CL: https://codereview.chromium.org/2665613003).

Multi-line strings must not preserve the physical line ending. Any line terminating sequence (CR+LF, CR-not-followed-by-LF or LF-not-preceded-by-CR) represents a line-break in the multi-line string, and a line-break adds a single newline character to the resulting string (unless it's the first one and it's only preceded by whitespace characters - I haven't gotten rid of the "backslash" exception, but I still want to).

A CR+BACKSLASH+LF is not a CR+LF sequence. I'm not sure exactly what BACKLASH+CR or BACKSLASH+LF means, though (BACKSLASH+CR+LF for that matter). It might need looking into, especially if it's at the end of a first whitespace-only line. I'd be happy to make it a compile-time error to put a backslash before a CR or LF.
As written, it's not allowed, the only thing that is allowed is backslashes before whitespace before the line terminator.