Go vet is telling me I'm copying a lock, when I don't think I am

Question

You can find the code I'm working on at: https://github.com/bigblind/marvin

gometalinter is giving me the following error from go vet:

accounts/interactors/accounts_test.go:16::error: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex (vet)

If you're not familiar with gometalinter, that shouldn't matter, it just runs other tools, including go vet.

So here's the code from accounts/interactors/accounts_test.go:16 with surrounding lines for context:

ma := accounts.NewMockAccountStore()
ma.On("SaveAccount", mock.AnythingOfType("Account")).Return(nil)
ca := CreateAccount{ma}

Line 16 is the last line of the snippet above. We're taking the result of accounts.NewMockAccountStore() and putting it in the first field of a newCreateAccount` struct.

Here's what MockAccountStore looks like:

type MockAccountStore struct {
    *mock.Mock
}

func NewMockAccountStore() *MockAccountStore {
    mo := mock.Mock{}
    ma := MockAccountStore{&mo}
    return &ma
}

As you can see here, I'm using pointers a lot. NewMockAccountStore returns a pointer to MockAccountStore, and the MockAccountStore contains a pointer to a mock.Mock.

So when I put this newly created MockAccountStore in my CreateAccount sturct, I'd expect that to basically just assign the pointer to that field, without copying anything.

Finally, let's have a look at the CreateAccount struct:

type CreateAccount struct {
    AccountStore domain.AccountStore
}

So CreateAccount has just one field for storing a domain.AccountStore. domain.AccountStore is an interface, which MockAccountStore implements.

The only explanation I can come up with is that assigning to a field that has an interface type somehow causes copying, but I'm not sure why, since as far as I'm aware, an interface value is just a pointer to the underlying type.

Can anyone explain to me why go vet is complaining?

---

Looks like I'm not actually copying.

I've changed my code as follows:

ma := accounts.NewMockAccountStore()
ma.On("SaveAccount", mock.AnythingOfType("Account")).Return(nil)
s := fmt.Sprintf("Initial %#v\n", ma)
ca := CreateAccount{ma}
panic(s + fmt.Sprintf("assigned: %#v", ca.AccountStore))

When the test containing this code runs, I get the following panic message:

Initial &accounts.MockAccountStore{Mock:(*mock.Mock)(0xc420019780)} assigned: &accounts.MockAccountStore{Mock:(*mock.Mock)(0xc420019780)}

As you can see, both values point to the same mock.Mock pointer (0xc420019780).

So how do I tell go vet that?

---

At @putu's request, here's the command output of accounts/interactors:

vet: accounts/interactors/accounts_test.go:8:2: could not import github.com/stretchr/testify/require (can't find import: github.com/bigblind/marvin/vendor/github.com/stretchr/testify/require)
Checking file accounts/interactors/accounts.go
Checking file accounts/interactors/login.go
Checking file accounts/interactors/accounts_test.go
accounts/interactors/accounts_test.go:15: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
accounts/interactors/accounts_test.go:28: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
accounts/interactors/accounts_test.go:35: github.com/bigblind/marvin/accounts/domain.Account composite literal uses unkeyed fields
accounts/interactors/accounts_test.go:40: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
Checking file accounts/interactors/login_test.go
accounts/interactors/login_test.go:22: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
accounts/interactors/login_test.go:36: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
accounts/interactors/login_test.go:47: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
accounts/interactors/login_test.go:58: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
accounts/interactors/login_test.go:70: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex
accounts/interactors/login_test.go:80: literal copies lock value from ma: github.com/bigblind/marvin/accounts.MockAccountStore contains github.com/bigblind/marvin/vendor/github.com/stretchr/testify/mock.Mock contains sync.Mutex