regitry.Repository does not implement content.ReadOnlyGraphStorage

[JefeDavis]

currently remote.NewRepository("myreg/myrepo") returns a remote.Repository object
but i use reg, err := remote.NewRegistry("myreg") and then call reg.Repository("myrepo") it returns a registry.Repository interface.

Unfortunately this interface is missing the Predecessors() method which means that it does not implement the content.ReadOnlyGraphStorage

this means that while i can use content.CopyGraph, i cannot use content.ExtendedCopyGraph

[shizhMSFT]

Thank @JefeDavis for mentioning this.
It is a breaking change to introduce content.PredecessorFinder in the Repository interface. Therefore, the change cannot be introduced to oras-go v2.
As a workaround, you can do type casting like

reg, err := remote.NewRegistry("myreg")
if err != nil {
    // handle error
}
repo, err := reg.Repository("myrepo")
if err != nil {
    // handle error
}
target, ok := repo.(content.GraphTarget)
if !ok {
    // handle exception
    // note that *remote.Repository implements oras.GraphTarget
}
// use target with Copy or ExtendedCopy