False negative with named return error

[maratori]

The following test fails

func TestFails() (err error) {
	err2 := func() error { return nil }()
	if err2 != nil {
		return // want `return a nil value error after check error`
	}
	return
}

I think that is a false negative because almost the same test passes

nilnesserr/testdata/src/nilnesserr/positive.go

Lines 83 to 93 in ef87e2e

	func Call12() (err error) {
	err = Do()
	if err != nil {
	return err
	}
	err2 := Do2()
	if err2 != nil {
	return // want `return a nil value error after check error`
	}
	return
	}

[alingse]

In this case, I don't think it is a false-positive.

if the user really want return a nil error, they may write code like this

func TestFails() (err error) {
	err2 := func() error { return nil }()
	if err2 != nil {
                // if they really want ignore some other err, they can return it directly
		return nil
	}
	return
}

[maratori]

It is a false negative, not a false positive.

[alingse]

My, My, I will look into it.

[alingse]

@maratori this case is hard to be solved in SSA

func Call18() (err error) {
	a := 1
	err2 := Do()
	if err2 != nil {
		if a > 0 {
			return // 1, should report `return a nil value error after check error`
		}
		return nil // 2
	}
	return nil // 3
}

the return branch 1/2/3 is all the same kind &ssa.Const{typ:(*types.Named)(0xc0001541c0), Value:constant.Value(nil)}

if the branch 1 is a false-negative, the branch 2 is the false-positive

you can see the report #1 here, the comment with a 👎point-down flag is the false-positive case.

• https://github.com/go-dev-frame/sponge/blob/main/pkg/encoding/json_encoding.go#L79
• https://github.com/go-gitea/gitea/blob/main/modules/activitypub/client.go#L95

( maybe we can combine the ssa and ast 🤔, but i don't think it's necessary