yaml: deprecate non-strict YAML

[AkihiroSuda]

Having duplicated keys is now prohibited, but having unsupported keys is still allowed (with deprecation warning)

Fix #1044

$ cat correct.yaml 
images:
- location: "https://cloud-images.ubuntu.com/releases/22.04/release/ubuntu-22.04-server-cloudimg-amd64.img"

networks:
- lima: shared
- lima: bridged

$ limactl validate correct.yaml 
INFO[0000] "correct.yaml": OK 

$ cat duplicated-key.yaml 
images:
- location: "https://cloud-images.ubuntu.com/releases/22.04/release/ubuntu-22.04-server-cloudimg-amd64.img"

networks:
- lima: shared
  lima: bridged

$ limactl validate duplicated-key.yaml 
FATA[0000] failed to load YAML file "duplicated-key.yaml": failed to unmarshal YAML (main file "/tmp/foo/duplicated-key.yaml"): [6:3] duplicate key "lima"
       4 | networks:
       5 | - lima: shared
    >  6 |   lima: bridged
             ^ 

$ cat unknown-key.yaml 
images:
- location: "https://cloud-images.ubuntu.com/releases/22.04/release/ubuntu-22.04-server-cloudimg-amd64.img"

networks:
- lima: shared
lima: bridged

$ limactl validate unknown-key.yaml 
WARN[0000] Non-strict YAML is deprecated and will be unsupported in a future version of Lima  comment="main file \"/tmp/foo/unknown-key.yaml\"" error="[6:1] unknown field \"lima\"\n       4 | networks:\n       5 | - lima: shared\n    >  6 | lima: bridged\n           ^"
INFO[0000] "unknown-key.yaml": OK

[jandubois]

LGTM, I'm fine with merging it.

I have 2 observations though, running it against a RD config that has already been updated with socketVMNet support for testing:

$ limactl validate ~/Library/Application\ Support/rancher-desktop/lima/0/lima.yaml
WARN[0000] Non-strict YAML is deprecated and will be unsupported in a future version of Lima  comment="main file \"/Users/jan/Library/Application Support/rancher-desktop/lima/0/lima.yaml\"" error="[150:1] unknown field \"k3s\"\n      147 |     lima-rancher-desktop: lima-0\n      148 |     host.rancher-desktop.internal: host.lima.internal\n      149 |     host.docker.internal: host.lima.internal\n    > 150 | k3s:\n            ^\n      151 |   version: 1.24.4"
FATA[0000] failed to load YAML file "/Users/jan/Library/Application Support/rancher-desktop/lima/0/lima.yaml": cannot parse "/Users/jan/.lima/_config/networks.yaml": [15:3] unknown field "socketVMNet"
      12 | paths:
      13 | # socketVMNet requires Lima >= 0.12 .
      14 | # socketVMNet has precedence over vdeVMNet.
    > 15 |   socketVMNet: /opt/socket_vmnet/bin/socket_vmnet
             ^
      16 | # vdeSwitch and vdeVMNet are DEPRECATED.
      17 |   vdeSwitch: /opt/vde/bin/vde_switch
      18 |   vdeVMNet: /opt/vde/bin/vde_vmnet
      19 |

The WARN output looks a lot less readable than the FATA output, due to the way the errors are reported. I think this is fine though, given that we will make "Strict" the default soon, so the warning will go away again. But if there is an easy fix for this, please apply it!

And the error about networks.yaml should not happen with the release version because by then the socketVMNet support will have been merged as well.

So despite these observations I'm fine with merging.