exportloopref
An analyzer that finds exporting pointers for loop variables.
Pin them all!
What's this?
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
Sensing policy
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.
Known false negatives
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)
}Install
go:
$ go get github.com/kyoh86/exportloopref/cmd/exportloopref$ brew install kyoh86/tap/exportloopref$ gordon install kyoh86/exportlooprefUsage
exportloopref [-flag] [package]
Flags
| 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) |
LICENSE
This is distributed under the MIT License.