YAML: duplicated keys should raise an error (with human-readable message)

[AkihiroSuda]

The following YAML is invalid but currently silently treated as a bridge-only YAML: #851 (comment)

networks:
- lima: shared
  lima: bridged
# ↑ typo of `- lima: bridged`

[jandubois]

I think all that is needed is to use https://pkg.go.dev/gopkg.in/yaml.v2#UnmarshalStrict

This should also catch user errors when they have a typo in a key name. Right now mistyped keys are silently ignored; in strict mode they will throw an error.

The drawback is that you can't store additional stuff in the file, e.g. Rancher Desktop currently stores the k3s version in lima.yaml:

k3s:
  version: 1.24.4

I don't know why it does this, as the version is also stored in its own settings file. But unconditionally switching to strict mode would mean that existing lima.yaml files would need to be cleaned before they could be used in an updated limactl.

Note that I'm in favour of turning on strict mode; I just wanted to point out the implications.

[AkihiroSuda]

Strict mode seems missing in v3?
https://pkg.go.dev/gopkg.in/yaml.v3

[AkihiroSuda]

This library might be useful
https://pkg.go.dev/github.com/goccy/go-yaml#DisallowDuplicateKey
https://pkg.go.dev/github.com/goccy/go-yaml#DisallowUnknownField