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What's the rule for lists? Which of these are acceptable/advisable?

var a = [1, 2, 3];
var b = [
  1,
  2,
  3
];
var c = [1, 2,
    3];
var d = [1, 2,
  3];

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a and b are acceptable, and I think it's up to the user to choose which one they want. c and d are always wrong.

I would probably have the formatter:

1. Control formatting after the "[".
2. Control indentation of every line in the list.
3. Control the formatting before the "]".
4. Preserve the users newlines after ",".

What about?

var pairs = [
  1, 2,
  3, 4,
  5, 6
];

As a user I'd be frustrated if this got flattened.

On the other hand, what should happen if I add another pair?

var pairs = [
  1, 2,
  3, 4,
  5, 6, 7, 8
]
  
Obviously we can't get into the business of trying to divine the semantic meaning of user-introduced whitespace.

And what about long lists? Is there an acceptable version that does not have one item per line?

This comment was originally written by @Fox32

I have a list defining a coordiantes for a cube with normals a texture coordinates. I want to use the formatter but the formatter will never be able to output it in the way I want it. Maybe it is better if the formatter don't touch the contents of the list. Then the user needs to do it on his own.

Here is the example for my list. I added additional whitespaces to make it easier to read (every number is lining up, even if it negativ) and to seperate the position from the normals and texture coordinates.

[
  [-0.5, -0.5, 0.5, 0.0, 0.0, -1.0, 0.0, 0.0,
    0.5, -0.5, 0.5, 0.0, 0.0, -1.0, 1.0, 0.0,
    0.5, 0.5, 0.5, 0.0, 0.0, -1.0, 1.0, 1.0,
   -0.5, 0.5, 0.5, 0.0, 0.0, -1.0, 0.0, 1.0],
  [-0.5, -0.5, 0.5, 1.0, 0.0, 0.0, 1.0, 1.0,
   -0.5, 0.5, 0.5, 1.0, 0.0, 0.0, 0.0, 1.0,
   -0.5, 0.5, -0.5, 1.0, 0.0, 0.0, 0.0, 0.0,
   -0.5, -0.5, -0.5, 1.0, 0.0, 0.0, 1.0, 0.0],
  [-0.5, 0.5, 0.5, 0.0, -1.0, 0.0, 1.0, 1.0,
    0.5, 0.5, 0.5, 0.0, -1.0, 0.0, 0.0, 1.0,
    0.5, 0.5, -0.5, 0.0, -1.0, 0.0, 0.0, 0.0,
   -0.5, 0.5, -0.5, 0.0, -1.0, 0.0, 1.0, 0.0],
  [ 0.5, 0.5, 0.5, -1.0, 0.0, 0.0, 1.0, 1.0,
    0.5, -0.5, 0.5, -1.0, 0.0, 0.0, 0.0, 1.0,
    0.5, -0.5, -0.5, -1.0, 0.0, 0.0, 0.0, 0.0,
    0.5, 0.5, -0.5, -1.0, 0.0, 0.0, 1.0, 0.0],
  [ 0.5, -0.5, 0.5, 0.0, 1.0, 0.0, 1.0, 1.0,
   -0.5, -0.5, 0.5, 0.0, 1.0, 0.0, 0.0, 1.0,
   -0.5, -0.5, -0.5, 0.0, 1.0, 0.0, 0.0, 0.0,
    0.5, -0.5, -0.5, 0.0, 1.0, 0.0, 1.0, 0.0]
],

Great example. Thanks for chiming in!

This is exactly why I'm leery of the formatter being too aggressive with lists.

A couple of off the cuff thoughts:

a) The formatter could ignore lists of this format:

l = [
 <contents here -- possibly on multiple lines>
];

assuming that if the author put contents on a separate newline they know what they're doing.

b) we could condition authors to use a doc convention to ensure their structure is left intact:

l = [
  [-0.5, -0.5, 0.5, 0.0, 0.0, -1.0, 0.0, 0.0,
     0.5, -0.5, 0.5, 0.0, 0.0, -1.0, 1.0, 0.0,
     0.5, 0.5, 0.5, 0.0, 0.0, -1.0, 1.0, 1.0,
   -0.5, 0.5, 0.5, 0.0, 0.0, -1.0, 0.0, 1.0],
...

(This will look familiar to eclipse Java users.)

I'm not in love with (b) but I'm curious what your gut reaction is...

This comment was originally written by @Fox32

I don't like version b), I think the assumption that the user knows what he does, if he adds spaces, is a good way.

I first liked the idea 3. from comment #­3, but this wouldn't work with the minus sign formatting thing in my example.

What about?

var pairs = [
1, 2,
3, 4,
5, 6
];

As a user I'd be frustrated if this got flattened.

Me too. Hence rule 4 above.

On the other hand, what should happen if I add another pair?

I'd preserve that formatting too, unless it goes over 80 columns.
 

And what about long lists? Is there an acceptable version that does not have one item per line?

Sure, you can have long inline lists if you want, as long as the fit 80 columns. Once they go over, you need a newline after the "[" and before the "]".

Sure, you can have long inline lists if you want, as long as the fit 80 columns. Once they go over, you need a
newline after the "[" and before the "]".

Cool. Am I right that this list:

var primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 87];

would be reformatted to:

(A)

var primes = [
  2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71,
  73, 79, 83, 87
];

?

On would it rather be:

(B)

var primes = [
  2,
  3,
  5,
  ...
];

?

I'd guess (A) based on the principle that that makes the fewest changes to the original code.

Good deal. (And phew!) [A] it is.

I'll make it be!

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This issue has been moved to dart-lang/dart_style#307.