v2.30.0 - Multiple variables per Dart declaration

Dart: multiple variables per declaration

A declaration could only introduce one variable, so the ordinary Dart form of declaring several at once was a syntax error:

void main() {
  num nr = 0.96, ng = 0.24, nb = 0.56;  // was: [SyntaxError] ";" expected

  print(nr);
  print(ng);
  print(nb);
}

Every declarator is now accepted, in a function body and at the top level, sharing the declared type and the final / const / late modifier of the first one. A declarator may omit its initializer (int a, b = 5;) and may read the ones before it (int p = 1, q = p + 1;), matching Dart's left-to-right initialization.

The declarators are expanded into one declaration each as the code is parsed, so translation emits the form every target already supports:

num nr = 0.96;
num ng = 0.24;
num nb = 0.56;

nr: float = 0.96
ng: float = 0.24
nb: float = 0.56

A for initializer still takes a single declarator: a for header has no place for the extra declarations the expansion produces, and the comma-separated form does not exist in every target language.

Full changelog: v2.29.0...v2.30.0