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

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.

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)?