exportloopref

exportloopref

An analyzer that finds exporting pointers for loop variables.

What's this?

Sample problem code from: https://github.com/kyoh86/exportloopref/blob/master/testdata/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 inner variable)
			vArray[1] = &p // not a diagnostic (x is inner 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 inner 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/master/testdata/fixed/fixed.go

Sensing policy

I want to make exportloopref as accurately as possible. So some cases of lints will be ignored.

e.g.

var s Foo
for _, p := []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.

Install

go get github.com/kyoh86/exportloopref

Usage

exportloopref [-flag] [package]

Flags

LICENSE

This is distributed under the MIT License.