GitLab

It's a lie! We:

1. Assume that our datastores are thread-safe all over the place, not bothering
   to check for this interface.
2. Implement this interface for, e.g., the mount datastore that _may not_ be
   thread-safe (depending on the sub-datastores).

Basically, there's no sane way to to do something like this in go. What we
_want_ is:

```rust
pub trait ThreadSafe {}

struct MyWrapper<D: Datastore> { ... }

impl<D: Datastore> ThreadSafe for MyWrapper<D> where D: ThreadSafe {}
```

Actually, we don't even need this because rust has already done all the hard
work with the `Sync` trait.

....

But we're using go which barely has types.

---

For completeness, it's actually possible to do this in go:

```go
type threadSafeMixin struct{}
func (threadSafeMixin) ThreadSafe() {}

func NewWrapper(d Datastore) Datastore {
  if _, ok := d.(ThreadSafe) {
    return &struct{myWrapper, threadSafeMixin}{myWrapper{d}, threadSafeMixin{}}
  }
  return &myWrapper{d}
}
```

Let's not.