40 columns                              |
>>> indentation
extension A on B {
z() => 0;
inc(int x) => ++x;
foo(int x) {
if (x == 0) {
return true;
}}}
<<<
extension A on B {
  z() => 0;
  inc(int x) => ++x;
  foo(int x) {
    if (x == 0) {
      return true;
    }
  }
}
>>> trailing space inside body
extension A on B {
  }
<<<
extension A on B {}
>>> leading space before "extension"
  extension A on B {
}
<<<
extension A on B {}
>>>
extension A on B  { int meaningOfLife() => 42; }
<<<
extension A on B {
  int meaningOfLife() => 42;
}
>>>
extension     A      on      B    {
  }
<<<
extension A on B {}
>>>
extension A on B{z() => 0;inc(int x) => ++x;}
<<<
extension A on B {
  z() => 0;
  inc(int x) => ++x;
}
>>> eats newlines
extension

A


on


B


{}
<<<
extension A on B {}
>>> require blank line after non-empty block-bodied members
extension A on B {
b() {;} c() => null; get d {;} get e => null; set f(value) {;
} set g(value) => null;}
<<<
extension A on B {
  b() {
    ;
  }

  c() => null;
  get d {
    ;
  }

  get e => null;
  set f(value) {
    ;
  }

  set g(value) => null;
}
>>> no required blank line after empty block-bodied members
extension A on B {
b() {} c() => null; get d {} get e => null; set f(value) {
} set g(value) => null;}
<<<
extension A on B {
  b() {}
  c() => null;
  get d {}
  get e => null;
  set f(value) {}
  set g(value) => null;
}
>>> blank line before and after extension
var x = 1;
extension A on B {}
var y = 2;
<<<
var x = 1;

extension A on B {}

var y = 2;
>>> generic extension
extension   A    <  T  ,  S > on B{}
<<<
extension A<T, S> on B {}
>>> unnamed extension
extension    on   B{}
<<<
extension on B {}
>>> unnamed generic extension
extension   <  T  ,  S  >    on   B{}
<<<
extension<T, S> on B {}