nerdctl save dismisses multiple tags for same image

[MathiasRudolphSec]

Description

When using nerdctl save for multiple tags that reverence the same image, only a single tag will be retained in the saved dump.

Steps to reproduce the issue

1. nerdctl pull quay.io/kiwigrid/k8s-sidecar:1.28.0
2. nerdctl pull kiwigrid/k8s-sidecar:1.28.0
3. nerdctl save quay.io/kiwigrid/k8s-sidecar:1.28.0 kiwigrid/k8s-sidecar:1.28.0 | pigz > images.tar.gz

Describe the results you received and expected

Result

nerdctl load -i images.tar.gz produces:

unpacking quay.io/kiwigrid/k8s-sidecar:1.28.0 (sha256:4166a019eeafd1f0fef4d867dc5f224f18d84ec8681dbb31f3ca258ecf07bcf2)...
Loaded image: quay.io/kiwigrid/k8s-sidecar:1.28.0

Expected Result

When I use docker to do the same:
docker save quay.io/kiwigrid/k8s-sidecar:1.28.0 kiwigrid/k8s-sidecar:1.28.0 | gzip > docker-save.tar.gz
the same nerdctl load produces:

unpacking quay.io/kiwigrid/k8s-sidecar:1.28.0 (sha256:40a8c7a9ef0598a807b908dc458a8057698b1f92a3c0c2fe4929a0d3700e5dc8)...
Loaded image: quay.io/kiwigrid/k8s-sidecar:1.28.0
unpacking docker.io/kiwigrid/k8s-sidecar:1.28.0 (sha256:40a8c7a9ef0598a807b908dc458a8057698b1f92a3c0c2fe4929a0d3700e5dc8)...
Loaded image: kiwigrid/k8s-sidecar:1.28.0

which is the expected behavior.

What version of nerdctl are you using?

Manually installed from gitlab releases.

> sudo nerdctl version
Client:
 Version:       v2.0.2
 OS/Arch:       linux/amd64
 Git commit:    1220ce7ec2701d485a9b1beeea63dae3da134fb5
 buildctl:
  Version:      v0.15.2
  GitCommit:    9e14164a1099d3e41b58fc879cbdd6f2b2edb04e

Server:
 containerd:
  Version:      v2.0.1
  GitCommit:    88aa2f531d6c2922003cc7929e51daf1c14caa0a
 runc:
  Version:      1.2.4
  GitCommit:    v1.2.4-0-g6c52b3fc

Also tried it with nerdctl 1.7.7 and containerd 1.7.25

Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

Host information

> nerdctl info
Client:
 Namespace:     default
 Debug Mode:    false

Server:
 Server Version: v2.0.1
 Storage Driver: overlayfs
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Log:     fluentd journald json-file none syslog
  Storage: native overlayfs
 Security Options:
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version:   5.14.0-503.19.1.el9_5.x86_64
 Operating System: AlmaLinux 9.5 (Teal Serval)
 OSType:           linux
 Architecture:     x86_64
 CPUs:             8
 Total Memory:     15.37GiB
 Name:             bioserver-jenkins
 ID:               6b3ff2a7-9b41-4887-83b9-cf21f3d80c71

WARNING: IPv4 forwarding is disabled
WARNING: bridge-nf-call-iptables is disabled
WARNING: bridge-nf-call-ip6tables is disabled