use containerd/reference/docker instead of docker/distribution

[thaJeztah]

splitting this off from #40961

similar PR can be found in moby/buildkit#2666, which removes the dependency on this package from BuildKit (only remaining use in the code now)

containerd now maintains a copy of the docker/distribution code under the
github.com/containerd/containerd/reference/docker package.

Let's switch to using that package, to remove the (direct) dependency on
github.com/docker/distribution.

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Ah, some fixes needed in a mock;

distribution/push_v2_test.go:404:4: cannot use repo (type *mockRepo) as type distribution.Repository in field value:
    *mockRepo does not implement distribution.Repository (wrong type for Named method)
        have Named() docker.Named
        want Named() "github.com/docker/docker/vendor/github.com/docker/distribution/reference".Named
distribution/push_v2_test.go:607:3: cannot use repo (type *mockRepoWithBlob) as type distribution.Repository in field value:
    *mockRepoWithBlob does not implement distribution.Repository (wrong type for Named method)
        have Named() docker.Named
        want Named() "github.com/docker/docker/vendor/github.com/docker/distribution/reference".Named
distribution/push_v2_test.go:638:5: cannot use &mockRepo{} (type *mockRepo) as type distribution.Repository in assignment:
    *mockRepo does not implement distribution.Repository (wrong type for Named method)
        have Named() docker.Named
        want Named() "github.com/docker/docker/vendor/github.com/docker/distribution/reference".Named

[thaJeztah]

So, the error is because the mockRepos do not implement this interface;

moby/vendor/github.com/docker/distribution/registry.go

Lines 96 to 99 in 7b9275c

	// Repository is a named collection of manifests and layers.
	type Repository interface {
	// Named returns the name of the repository.
	Named() reference.Named

But I feel silly now; not sure I understand; so the failure is because I swapped the imports. Now, that makes perfect sense if the returned type was a "type", but it's an interface, so this line:

moby/distribution/push_v2_test.go

Lines 640 to 643 in 7b9275c

	func (m *mockRepo) Named() reference.Named {
	m.t.Fatalf("Named() not implemented")
	return nil
	}

• Previously returned github.com/docker/distribution/reference.Named
• But now returns github.com/containerd/containerd/reference/docker.Named

So.. how do they differ? Well.. they don't. The containerd reference/docker package is a copy of distribution's reference package;

Here's the docker/distribution definition:

moby/vendor/github.com/docker/distribution/reference/reference.go

Lines 63 to 68 in 7b9275c

	// Reference is an opaque object reference identifier that may include
	// modifiers such as a hostname, name, tag, and digest.
	type Reference interface {
	// String returns the full reference
	String() string
	}

moby/vendor/github.com/docker/distribution/reference/reference.go

Lines 108 to 112 in 7b9275c

	// Named is an object with a full name
	type Named interface {
	Reference
	Name() string
	}

And here's the containerd definition:

moby/vendor/github.com/containerd/containerd/reference/docker/reference.go

Lines 81 to 86 in 7b9275c

	// Reference is an opaque object reference identifier that may include
	// modifiers such as a hostname, name, tag, and digest.
	type Reference interface {
	// String returns the full reference
	String() string
	}

moby/vendor/github.com/containerd/containerd/reference/docker/reference.go

Lines 126 to 130 in 7b9275c

	// Named is an object with a full name
	type Named interface {
	Reference
	Name() string
	}

So, I would expect things to fail if those definitions depended on some type, but they're defining an interface that returns a generic (string) type.

A smaller example; https://go.dev/play/p/cRwQGtWCZi9

package main

import "fmt"

type Named interface {
	Name() string
}

type NamedTwo interface {
	Name() string
}

type Registry interface {
	Named() Named
}

// implementNamed implements Named, NamedTwo interface.
type implementNamed struct{ name string }

func (n *implementNamed) Name() string {
	return n.name
}

type oneRegistry struct{}

func (r *oneRegistry) Named() Named {
	return &implementNamed{"one"}
}

type twoRegistry struct{}

func (r *twoRegistry) Named() NamedTwo {
	return &implementNamed{"two"}
}

func main() {
	oneReg := oneRegistry{}
	twoReg := twoRegistry{}

	expectNamed(oneReg.Named())
	expectNamed(twoReg.Named())
	expectNamedTwo(oneReg.Named())
	expectNamedTwo(twoReg.Named())

	type thingWithNamed struct {
		named Named
	}

	// This works; even though twoReg.Named() returns a NamedTwo
	foo := thingWithNamed{}
	foo.named = oneReg.Named()
	fmt.Println(foo.named.Name())

	foo.named = twoReg.Named()
	fmt.Println(foo.named.Name())

	type thingWithRegistry struct {
		registry Registry
	}

	bar := thingWithRegistry{}
	bar.registry = &oneReg

	// But this doesn't work:
	// ./main.go:60:15: cannot use &twoReg (type *twoRegistry) as type Registry in assignment:
	// *twoRegistry does not implement Registry (wrong type for Named method)
	// have Named() NamedTwo
	// want Named() Named

	// bar.registry = &twoReg
}

func expectNamed(in Named) {
	fmt.Println("expectNamed:    " + in.Name())
}

func expectNamedTwo(in NamedTwo) {
	fmt.Println("expectNamedTwo: " + in.Name())
}

[thaJeztah]

As it looks like the "interface" issues really only affects this Mock, I decided to import the "old" package here. "production" code doesn't need the old interface

Not sure if there's a better solution for this; perhaps we should replace the distribution.Repository interface with something local if possible (haven't dug too deeply into that yet)

[tianon]

Relevant to what we discussed in the maintainers meeting, it appears this was copied into containerd specifically for containerd/containerd#3554 (via containerd/containerd#3728).

Was there ever any communication with either party about maintaining it in a separate (smaller) place? Now there are two copies that have diverged slightly and it'd be neat if we could help get them back in sync. 🙈

[thaJeztah]

• superseded by migrate to new github.com/distribution/reference module #46376