gofumpt -w foo.go
cmp foo.go foo.go.golden

gofumpt -d foo.go.golden
! stdout .

-- foo.go --
package p

var _ = []int{}

var _ = []int{
}

var _ = []int{1, 2,
	3, 4}

var _ = []int{
	1, 2, 3, 4}

var _ = [][]string{{
	"no need for more newlines",
	"if wrapping a single expression",
}}

var _ = []string{`
	no need for newlines
	`, `
	if no elements are surrounded by newlines
`}

var _ = []struct{ a int }{
	{ // consistent
		a: 1,
	},
	{
		a: 2,
	}, { // inconsistent
		a: 3,
	},
}

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

-- foo.go.golden --
package p

var _ = []int{}

var _ = []int{}

var _ = []int{
	1, 2,
	3, 4,
}

var _ = []int{
	1, 2, 3, 4,
}

var _ = [][]string{{
	"no need for more newlines",
	"if wrapping a single expression",
}}

var _ = []string{`
	no need for newlines
	`, `
	if no elements are surrounded by newlines
`}

var _ = []struct{ a int }{
	{ // consistent
		a: 1,
	},
	{
		a: 2,
	},
	{ // inconsistent
		a: 3,
	},
}

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