Upsert with custom Storer delivers inconsistent value type to index function

[justinfx]

When implementing a custom Storer on a type, I have found that during an Upsert, if the value already exists, the reflection logic ends up passing an **Item instead of *Item to the index function. This inconsistent type seems to be handled fine in the anonStorer reflection logic, but breaks a custom index function that expects to always get the same type. I'm currently working around this by type checking the value in each index function for **Item and dereferencing it once as needed to cope with the delete.

Here is a simple reproduction of the panic. Am I doing something wrong here?

type Item struct{ Name string }
func (i *Item) Type() string { return "Item" }
func (i *Item) Indexes() map[string]bh.Index {
    return map[string]bh.Index{
        "Name": func(_ string, value interface{}) ([]byte, error) {
            // If the upsert wants to delete an existing value first,
            // value could be a **Item instead of *Item
            // panic: interface conversion: interface {} is **Item, not *Item
            v := value.(*Item).Name
            return []byte(v), nil
        },
    }
}
func (i *Item) SliceIndexes() map[string]bh.SliceIndex {
    return map[string]bh.SliceIndex{}
}
func TestStorerUpsert(t *testing.T) {
    path := "/tmp/bolthold_upsert_test.db"
    os.Remove(path)
    db, err := bh.Open(path, 0666, nil)
    if err != nil {
        t.Fatal(err)
    }
    defer db.Close()
    item := &Item{"Name"}
    for i := 0; i < 2; i++ {
        err = db.Upsert("key", item)
        if err != nil {
            t.Fatal(err)
        }
    }
}

Originally mentioned in #64

[timshannon]

Let me know if you run into any more issues like this. There were a couple places where I was assuming none-pointers.

Thanks for reporting the issue.

[justinfx]

Very cool. Thanks for this fix! I will submit any other issues that I discover.