cmd/vet: error when returning `nil` inside an `if err != nil` clause

[cgrushko]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

version 1.10

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

amd64, linux

What did you do?

I mistakenly return nil inside a if err != nil clause, which hid a bug in my code. Since it almost never makes sense to return nil in such a case, I thought it'd be a nice go vet error.

func f() error {
err := ....
if err != nil {
return nil
}
return nil
}

[mvdan]

This seems like it will bring quite a few false positives. Have you prototyped such a change, and seen what it finds in the Go tree?

[dgryski]

Seems like the title should be "returning nil inside if err != nil" instead of "returning err inside if err != nil".

[adamdecaf]

Here's a valid return nil from the stdlib. I agree this will bring a lot of false positives.

https://github.com/golang/go/blob/release-branch.go1.10/src/crypto/x509/root_darwin.go#L213-L225

[cgrushko]

This example is not what I suggest catching, because the if clause contains things other than return nil.

[mvdan]

Other reasonable scenarios come to mind, for example:

• Getting io.EOF but returning nil, because it was expected
• Funcs whose return type isn't error (perhaps obvious, but this issue does not clarify that)
• Expecting an operation to fail, thus returning a nil error when an obtained error is non-nil

And there's also the can of worms that is errors that are always nil. This kind of check probably belongs in a tool that gives a human suggestions, and not a linter that gives warnings that must be accurate.

[josharian]

cc @robpike for a final decision, but I think the likely false positives from this make it not a good fit for vet.

cc also @dominikh in general for all things that don’t make it into vet. :)

[robpike]

Fails the precision criterion of cmd/vet/README.