StringConversionSink.asStringSink() and asUtf8Sink() don't invalidate this

[sgrekhov]

Please see StringConversionSink.asStringSink() documentation at https://api.dartlang.org/stable/1.22.1/dart-convert/StringConversionSink/asStringSink.html

ClosableStringSink asStringSink()
Returns this as a ClosableStringSink.

If used, this method must be the first and only call to this. It invalidates this. All further operations must be performed on the result.

Now look at the following code.

import "dart:convert";
main() {
  var outSink = new ByteConversionSink.withCallback((accumulated) {
    print(accumulated);
  });

  StringConversionSink inSink = UTF8.encoder.startChunkedConversion(outSink);
  inSink.add("1");

  ClosableStringSink css = inSink.asStringSink();
  css.write("2");
  inSink.add("3");
  css.close(); // prints [49, 50, 51]. It's encoded string "123"
  inSink.add("4");
  inSink.close(); // prints [49, 50, 51, 52]. It's encoded string "1234"
  inSink.add("5");
  inSink.close(); // prints [49, 50, 51, 52, 53]. It's encoded string "12345"
}

I don't see that asStringSink() invalidates anything.

The same is true for StringConversionSink.asUtf8Sink()

import "dart:convert";
main() {
  var outSink = new ByteConversionSink.withCallback((accumulated) {
    print(accumulated);
  });

  StringConversionSink inSink = UTF8.encoder.startChunkedConversion(outSink);
  inSink.add("1");

  ByteConversionSink bcs = inSink.asUtf8Sink(false);
  bcs.add([50]); // [50] is utf-8 encoding of 2
  inSink.add("3");
  bcs.close(); // prints [49, 50, 51]. It's encoded string "123"
  inSink.add("4");
  inSink.close(); // prints [49, 50, 51, 52]. It's encoded string "1234"
  inSink.add("5");
  inSink.close(); // prints [49, 50, 51, 52, 53]. It's encoded string "12345"
}