looppointer
An analyzer that finds pointers for loop variables.
What's this?
Sample problem code from: https://github.com/kyoh86/looppointer/blob/main/testdata/simple/simple.go
package main
func main() {
var intSlice []*int
println("loop expecting 10, 11, 12, 13")
for _, p := range []int{10, 11, 12, 13} {
intSlice = append(intSlice, &p) // want "taking a pointer for the loop variable p"
}
println(`slice expecting "10, 11, 12, 13" but "13, 13, 13, 13"`)
for _, p := range intSlice {
printp(p)
}
}
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 looppointer, and fix it.
package main
func main() {
var intSlice []*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
intSlice = append(intSlice, &p)
}
println(`slice expecting "10, 11, 12, 13"`)
for _, p := range intSlice {
printp(p)
}
}
func printp(p *int) {
println(*p)
}ref: https://github.com/kyoh86/looppointer/blob/main/testdata/fixed/fixed.go
Sensing policy
I want to make looppointer as nervous as possible. So some false-positves will be reported.
e.g.
func TestSample(t *testing.T) {
for _, p := []int{10, 11, 12, 13} {
t.Run(func(t *testing.T) {
s = &p // t.Run always called instantly, so it will not be bug.
...
})
}
}They can be escaped with pining-variable:
func TestSample(t *testing.T) {
for _, p := []int{10, 11, 12, 13} {
p := p // pin a variable to local in the loop
t.Run(func(t *testing.T) {
s = &p
...
})
}
}If you want to ignore false-positives (with some lints ignored), you should use exportloopref.
Nolint
Diagnostics by looppointer can be suppress with the line comment // nolint:looppointer.
func TestSample(t *testing.T) {
for _, p := []int{10, 11, 12, 13} {
t.Run(func(t *testing.T) {
s = &p // nolint
...
})
}
}Install
go:
$ go get github.com/kyoh86/looppointer/cmd/looppointer$ brew install kyoh86/tap/looppointer$ gordon install kyoh86/looppointerUsage
looppointer [-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.