cmd/gofmt: slice of structs not consistently formatted

[smasher164]

See https://play.golang.org/p/uwG_GFPiU13.
I expected the literal to be reformatted like this:

package main

func main() {
	_ = []struct{ a int }{
		{
			a: 1,
		},
		{
			a: 2,
		},
		{
			a: 3,
		},
	}
}

instead, it preserves the previous formatting.

package main

func main() {
	_ = []struct{ a int }{
		{
			a: 1,
		},
		{
			a: 2,
		}, {
			a: 3,
		},
	}
}

Is this intentional? Or does it make sense to keep the formatting of structs in the slice the same?

[mdempsky]

/cc @griesemer

[agnivade]

Both

},
{

and }, { are allowed.

To make different styles fall to a single one in a single declaration, we would have to keep track of braces and their positions and then possibly go backwards and change token positions.

Up to Robert to decide to do it or not.

[mvdan]

I personally think this would be nice to have, if it doesn't add a lot of complexity to gofmt.

[griesemer]

Nice to have, but complicated to get right, I suspect. In general, where multiple formats are accepted, we defer to the user.

[mvdan]

I've implemented a prototype at mvdan/gofumpt@5d37481 if anyone wants to play with it. The solution is pretty straightforward there, but I already had some logic to determine if a composite literal had any newlines between its elements.

[smasher164]

Thank you for working on this!
I tried out mvdan/gofumpt@5d37481, but it enforces that

},
{

is applied in all cases. For example,

_ = []struct{ a int }{
    {a: 1}, {
        a: 2,
    }, {
        a: 3,
    },
}

It is not obvious to me that the above literal gets reformatted into

_ = []struct{ a int }{
    {a: 1},
    {
        a: 2,
    },
    {
        a: 3,
    },
}

What gets determined to be the consistent style? The only one I can think of is the style of the first element in the list gets applied to the subsequent elements.

[mvdan]

Thanks for the report, @smasher164. Let's take this to mvdan/gofumpt#36, since the bug doesn't concern gofmt.