c8d: inconsistent presentation of ARM64 images (linux/arm64 vs linux/arm64/v8)

Description

From https://github.com/moby/moby/issues/48604 by @thaJeztah

Description

I noticed that there's some inconsistency in presentation of arm64 platforms; one of my images was built with linux/arm64 (no variant), and it looks like we present this as-is.

docker image ls --tree
WARNING: This is an experimental feature. The output may change and shouldn't be depended on.

IMAGE                      ID             DISK USAGE   CONTENT SIZE   USED
alpine:latest              beefdbd8a1da       13.6MB         4.09MB
├─ linux/arm64/v8          9cee2b382fe2       13.6MB         4.09MB
├─ linux/amd64             33735bd63cf8           0B             0B
├─ linux/arm/v6            50f635c8b04d           0B             0B
├─ linux/arm/v7            f2f82d424957           0B             0B
├─ linux/386               b3e87f642f5c           0B             0B
├─ linux/ppc64le           c7a6800e3dc5           0B             0B
├─ linux/riscv64           80cde017a105           0B             0B
└─ linux/s390x             2b5b26e09ca2           0B             0B

thajeztah/ddshell:latest   e332ae952d63       23.8MB         7.88MB    ✔
├─ linux/arm64             1b9c0c672878       23.8MB         7.88MB    ✔
└─ linux/amd64             65b8d31def37           0B             0B

AFAIK, linux/arm64 is always equivalent to linux/arm64/v8

docker pull --platform=linux/arm64 thajeztah/ddshell:latest
latest: Pulling from thajeztah/ddshell
8f5adf85e8b9: Download complete
9b3977197b4f: Download complete
414aa140181c: Download complete
b8a650d25df2: Download complete
Digest: sha256:e332ae952d6326b017e64cbb66f2514906e8d9cad56dc5d554e7cd6474f1cd45
Status: Downloaded newer image for thajeztah/ddshell:latest
docker.io/thajeztah/ddshell:latest

docker pull --platform=linux/arm64/v8 thajeztah/ddshell:latest
latest: Pulling from thajeztah/ddshell
Digest: sha256:e332ae952d6326b017e64cbb66f2514906e8d9cad56dc5d554e7cd6474f1cd45
Status: Image is up to date for thajeztah/ddshell:latest
docker.io/thajeztah/ddshell:latest

I wonder if

• we should present it in its canonical / fully-qualified format, or if we should continue presenting as-is
• ❓ would there ever be ambiguity once a v9 becomes available (and in that case, would linux/arm64 be equal to linux/arm64/v9 ?)
• ❓ if we do want to present in canonical form, should we consider that presentation (i.e., handle this on the CLI side), or should this be done on the API side (API doing normalizing)?

Start with the docker image ls --tree entry point and trace how platform names are selected for display. The issue names no files or tests and leaves canonicalization, API behavior, and future ARM64 variants unresolved; a decision on the desired representation would be needed before implementation and validation.