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

gofumpt -d foo.go.golden
! stdout .

-- foo.go --
// +build tag

package p

//go:generate some command

//go:unknowndirective

//lint:disablefoo

//nolint

//nolint // explanation

//nolint:somelinter // explanation

//not actually: a directive

//TODO: do something

//export CgoFunc

//extern open
func c_open(name *byte, mode int, perm int) int

//line 123

//sys   Unlink(path string) (err error)

//sysnb	Getpid() (pid int)

//foo is foo.
type foo int

//	comment with a tab.

//  comment with many spaces

//comment group
//123 numbers too

// comment group
//123 numbers too

//{
//this is probably code
//}

////////////
// ascii art
//----------

//
-- foo.go.golden --
// +build tag

package p

//go:generate some command

//go:unknowndirective

//lint:disablefoo

//nolint

//nolint // explanation

//nolint:somelinter // explanation

// not actually: a directive

// TODO: do something

//export CgoFunc

//extern open
func c_open(name *byte, mode int, perm int) int

//line 123

//sys   Unlink(path string) (err error)

//sysnb	Getpid() (pid int)

// foo is foo.
type foo int

//	comment with a tab.

//  comment with many spaces

// comment group
// 123 numbers too

// comment group
// 123 numbers too

//{
//this is probably code
//}

////////////
// ascii art
//----------

//