Go-tools: False positive on U1000: "unused type" is actually used

[lupine]

Hi,

Our verify jobs started failing about an hour ago with this error: https://gitlab.com/nick.thomas/gitlab-workhorse/-/jobs/194368582 -> https://gitlab.com/gitlab-org/gitlab-workhorse/issues/217

internal/gitaly/gitaly.go:25:6: type connectionsCache is unused (U1000)

Here's a minimal reproducer:

package foo

type connectionsCache struct {
    foo string
}

var (
    cache = connectionsCache{
        foo: "Foo",
    }
)

func Foo() string {
    return cache.foo
}

And console output:

staticcheck foo.go
foo.go:4:6: type connectionsCache is unused (U1000)

I see https://github.com/dominikh/go-tools/issues/416 was closed just 4 hours ago - perhaps it's a regression caused by that fix?

[cierpuchaw]

I was just about to report this. In case it might be useful, here's a different reproducer (using type aliases):

package main

import "fmt"

type someStringer struct{}

func (someStringer) String() string {
    return "stuff"
}

type firstAlias = someStringer
type secondAlias = someStringer

func main() {
    stringers := []fmt.Stringer{&firstAlias{}, &secondAlias{}}
    for _, c := range stringers {
        fmt.Println(c)
    }
}

output:

u1000repro.go:11:6: type firstAlias is unused (U1000)
u1000repro.go:12:6: type secondAlias is unused (U1000)

[dominikh]

The first issue was fixed by bf9787c127f89e734632306cbd00b834786386ce – the second issue is a separate one I am currently working on.

[lupine]

Thanks for looking into this so quickly @dominikh !

Your new commit fixes my minimal repro above, but looking at the full pipeline, it now fails with something most unexpected: https://gitlab.com/nick.thomas/gitlab-workhorse/-/jobs/194403408

honnef.co/go/tools/unused/unused.go:1272:15: field.Embedded undefined (type *types.Var has no field or method Embedded)

Sorry to be such a pain! I've tried looking at the source, but I'm finding it quite difficult to jump straight into it.

[dominikh]

The second issue was fixed by 6da49aace82e94acd4695e7867d968dda0e456a6

[dominikh]

@lupine (*go/types.Var).Embedded was added in Go 1.11 – We, much like the rest of the Go ecosystem, support the last two versions of Go. Currently that is 1.11 and 1.12. You seem to be using an older version.

[dominikh]

Embedded seems to be a synonym for Anonymous, which has been around since Go 1.5, and we could switch to it. However, one of our crucial dependencies, go/packages, already dropped support for Go 1.10, so you'd be out of luck the moment you update that, anyway.

[lupine]

No problem, thanks for explaining. I was worried it was another regression introduced by the new commit, is all!

[cierpuchaw]

The second issue was fixed by 6da49aa

Thanks!

[lootek]

Hi, same here. And yet another reproduction case:

code:

package main

type AA interface {
    A()
}

type BB interface {
    AA
}

type CC interface {
    BB
    C()
}

func c(cc CC) {
    cc.A()
}

type z struct{}

func (z) A() {
    //
}

func (z) B() {
    //
}

func (z) C() {
    //
}

func main() {
    c(z{})
}

output:

$ staticcheck u1000repro.go 
u1000repro.go:7:6: type BB is unused (U1000)

[dominikh]

@lootek Fixed in 747de16c19d0445d584b301957201f6060367166