An analyzer that finds exporting pointers for loop variables. Pin them all!
As of Go 1.22, this problem no longer occurs and fixed by Go team, see here
Sample problem code from: https://github.com/kyoh86/exportloopref/blob/main/testdata/src/simple/simple.go
package main
func main() {
var intArray [4]*int
var intSlice []*int
var intRef *int
var intStr struct{ x *int }
println("loop expecting 10, 11, 12, 13")
for i, p := range []int{10, 11, 12, 13} {
printp(&p) // not a diagnostic
intSlice = append(intSlice, &p) // want "exporting a pointer for the loop variable p"
intArray[i] = &p // want "exporting a pointer for the loop variable p"
if i%2 == 0 {
intRef = &p // want "exporting a pointer for the loop variable p"
intStr.x = &p // want "exporting a pointer for the loop variable p"
}
var vStr struct{ x *int }
var vArray [4]*int
var v *int
if i%2 == 0 {
v = &p // not a diagnostic (x is local variable)
vArray[1] = &p // not a diagnostic (x is local variable)
vStr.x = &p
}
_ = v
}
println(`slice expecting "10, 11, 12, 13" but "13, 13, 13, 13"`)
for _, p := range intSlice {
printp(p)
}
println(`array expecting "10, 11, 12, 13" but "13, 13, 13, 13"`)
for _, p := range intArray {
printp(p)
}
println(`captured value expecting "12" but "13"`)
printp(intRef)
}
func printp(p *int) {
println(*p)
}
In Go, the p
variable in the above loops is actually a single variable.
So in many case (like the above), using it makes for us annoying bugs.
You can find them with exportloopref
, and fix it.
package main
func main() {
var intArray [4]*int
var intSlice []*int
var intRef *int
var intStr struct{ x *int }
println("loop expecting 10, 11, 12, 13")
for i, p := range []int{10, 11, 12, 13} {
p := p // FIX variable into the local variable
printp(&p)
intSlice = append(intSlice, &p)
intArray[i] = &p
if i%2 == 0 {
intRef = &p
intStr.x = &p
}
var vStr struct{ x *int }
var vArray [4]*int
var v *int
if i%2 == 0 {
v = &p
vArray[1] = &p
vStr.x = &p
}
_ = v
}
println(`slice expecting "10, 11, 12, 13"`)
for _, p := range intSlice {
printp(p)
}
println(`array expecting "10, 11, 12, 13"`)
for _, p := range intArray {
printp(p)
}
println(`captured value expecting "12"`)
printp(intRef)
}
func printp(p *int) {
println(*p)
}
ref: https://github.com/kyoh86/exportloopref/blob/main/testdata/src/fixed/fixed.go
I want to make exportloopref as accurately as possible. So some cases of lints will be false-negative.
e.g.
var s Foo
for _, p := range []int{10, 11, 12, 13} {
s.Bar(&p) // If s stores the pointer, it will be bug.
}
If you want to report all of lints (with some false-positives), you should use looppointer.
Case 1: pass the pointer to function to export.
Case 2: pass the pointer to local variable, and export it.
package main
type List []*int
func (l *List) AppendP(p *int) {
*l = append(*l, p)
}
func main() {
var slice []*int
list := List{}
println("loop expect exporting 10, 11, 12, 13")
for _, v := range []int{10, 11, 12, 13} {
list.AppendP(&v) // Case 1: wanted "exporting a pointer for the loop variable v", but cannot be found
p := &v // p is the local variable
slice = append(slice, p) // Case 2: wanted "exporting a pointer for the loop variable v", but cannot be found
}
println(`slice expecting "10, 11, 12, 13" but "13, 13, 13, 13"`)
for _, p := range slice {
printp(p)
}
println(`array expecting "10, 11, 12, 13" but "13, 13, 13, 13"`)
for _, p := range ([]*int)(list) {
printp(p)
}
}
func printp(p *int) {
println(*p)
}
go:
$ go install github.com/kyoh86/exportloopref/cmd/exportloopref@latest
$ brew install kyoh86/tap/exportloopref
$ gordon install kyoh86/exportloopref
exportloopref [-flag] [package]
Flag | Description |
---|---|
-V | print version and exit |
-all | no effect (deprecated) |
-c int | display offending line with this many lines of context (default -1) |
-cpuprofile string | write CPU profile to this file |
-debug string | debug flags, any subset of "fpstv" |
-fix | apply all suggested fixes |
-flags | print analyzer flags in JSON |
-json | emit JSON output |
-memprofile string | write memory profile to this file |
-source | no effect (deprecated) |
-tags string | no effect (deprecated) |
-trace string | write trace log to this file |
-v | no effect (deprecated) |
This is distributed under the MIT License.