RootFS.layers entry added for operations that do not impact the filesystem

[komish]

Issue Description

I've noticed that buildah build and podman build --squash both produce a RootFS layer of sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef even if there are no RootFS-impacting instructions in the Containerfile. Observing an image with this layer, it contains no content but still ends in the RootFS.layers blob.

Steps to reproduce the issue

Steps to reproduce the issue

1. Build this image using buildah build <file>

from registry.fedoraproject.org/fedora@sha256:dd93b388ec7b1da2055d2234532499526cef6a799de80f95a923f293602dd462 as base

LABEL foo=bar

❯ podman image inspect <imageid> | jq '.[0].RootFS.Layers'
[
  "sha256:35fccc735c0f5e9fe7c672e3162d8ee5b515e21d0de850026752bb4c1806a51a",
  "sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef"
]

3. Optionally inspect the content associated with sha256:5f70b... and notice it's empty.

Describe the results you received

"sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef" shows up as the final layer in RootFS.Layers for the image.

Describe the results you expected

As it does not contain filesystem-impacting content, I would not expect this to be in the RootFS.Layers list.

buildah version output

VERSION: buildah version 1.43.1 (image-spec 1.1.1, runtime-spec 1.2.1)
RPM: buildah-1.43.1-1.fc43.x86_64

buildah info output

{
    "host": {
        "CgroupVersion": "v2",
        "Distribution": {
            "distribution": "fedora",
            "version": "43"
        },
        "MemFree": 1716559872,
        "MemTotal": 67100418048,
        "OCIRuntime": "crun",
        "SwapFree": 8310710272,
        "SwapTotal": 8589930496,
        "arch": "amd64",
        "cpus": 16,
        "hostname": "my-hostname",
        "kernel": "7.0.8-100.fc43.x86_64",
        "os": "linux",
        "rootless": true,
        "uptime": "73h 52m 44.22s (Approximately 3.04 days)",
        "variant": ""
    },
    "store": {
        "ContainerStore": {
            "number": 107
        },
        "GraphDriverName": "overlay",
        "GraphImageStore": "",
        "GraphOptions": null,
        "GraphRoot": "/home/username/.local/share/containers/storage",
        "GraphStatus": {
            "Backing Filesystem": "btrfs",
            "Native Overlay Diff": "true",
            "Supports d_type": "true",
            "Supports shifting": "false",
            "Supports volatile": "true",
            "Using metacopy": "false"
        },
        "GraphTransientStore": false,
        "ImageStore": {
            "number": 891
        },
        "RunRoot": "/run/user/107112/containers"
    }
}

Provide your storage.conf

n/a

Upstream Latest Release

Yes

Additional environment details

Additional environment details

Additional information

No response

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