[New rule] Always put a newline between statements

[dagba]

This rule requires or disallows blank lines between the given 2 kinds of statements. Properly blank lines help developers to understand the code.

For example, the following configuration requires a blank line between a variable declaration and a return statement.

Bad:

class MyClass {
  static const _defaultVariable1 = 0.0;
  static const _defaultVariable2 = 0.0;
  final String variable1;
  final String variable2;
  const MyClass({
    required this.variable1,
    required this.variable2,
  });
  void doSomething() {
    // doSomething
  }
}

int foo() {
  var a = 1;
  return a;
}

void foo() {
  const a = 0;
  const b = 0;
  bar();
}

var greet = "hello,",
var name = "world";
log(greet, name);
var greet = "hello,",
var name = "world";
log(greet, name);
var greet = "hello,";
var name = "world";
log(greet, NAME);
var greet = "hello,";
var name = "world";
log(greet, name);

Good:

class MyClass {
  static const _defaultVariable1 = 0.0;
  static const _defaultVariable2 = 0.0;

  final String variable1;
  final String variable2;

  const MyClass({
    required this.variable1,
    required this.variable2,
  });

  void doSomething() {
    // doSomething
  }
}

int foo() {
  var a = 1;

  return a;
}

void foo() {
  const a = 0;
  const b = 0;

  bar();
}

var greet = "hello,",
var name = "world";
log(greet, name);

var greet = "hello,",
var name = "world";
log(greet, name);

var greet = "hello,";
var name = "world";
log(greet, NAME);

var greet = "hello,";
var name = "world";
log(greet, name);