goreduce

Reduce a program to its simplest form as long as it produces a compiler error or any output (such as a panic) matching a regular expression.

go get -u mvdan.cc/goreduce

Example

func main() {
        a := []int{1, 2, 3}
        if true {
                a = append(a, 4)
        }
        a[1] = -2
        println(a[10])
}

goreduce -match 'index out of range' .

func main() {
        a := []int{}
        println(a[0])
}

For more usage information, see goreduce -h.

Design

• The tool should be reproducible, giving the same output for an input program as long as external factors don't modify its behavior
• The rules should be as simple and composable as possible
• Rules should avoid generating changes that they can know won't compile

Rules

Removing

	Before	After
statement	a; b	a or b
index	a[1]	a
slice	a[:2]	a or a[:]
binary part	a + b, a && b	a or b
unary op	-a, !a	a
star	*a	a
parentheses	(a)	a
if/else	if a { b } else c	b or c
defer	defer f()	f()
go	go f()	f()
basic value	123, "foo"	0, ""
composite value	T{a, b}	T{}

Inlining

	Before	After
const	const c = 0; f(c)	f(0)
var	v := false; f(v)	f(false)
case	case x: a	a
block	{ a }	a
simple call	f()	{ body }

Resolving

	Before	After
integer op	2 * 3	6
string op	"foo" + "bar"	"foobar"
slice	"foo"[1:]	"oo"
index	"foo"[0]	'f'
builtin	len("foo")	3