Special-case decorator-style methods

[nex3]

I use the following pattern occasionally to simulate decorators; that is, to wrap the body of a method in some block or another to modify its behavior. It avoids extra indentation and looks nice, without being too complex:

Future doThing() => pool.withResource(() {
  // ...
});

Currently, the formatter formats this like so:

Future doThing() => pool.withResource(() {
      // ...
    });

It would be nice if it recognized the specific pattern of a => method with a block-format body and indented it like a normal method body.

[seaneagan]

per the style guide

[munificent]

You're right, @seaneagan, though we also need to tweak the style guide a bit in light of the formatter's more complex handling of nested function arguments. The original style guide rules just produce really nasty output in some cases.

Relevant style guide bug: dart-archive/www.dartlang.org#1397

[munificent]

The forthcoming tall style supports exactly this. You get:

Future doThing() => pool.withResource(() {
  // ...
});