Deserialize either a Sequence or a Mapping

[rcdailey]

There's a YAML configuration file that my application loads:

sonarr:
- base_url: abc1
  api_key: xyz1
- base_url: abc2
  api_key: xyz2

I want to change the schema for this to use a mapping (for named instances) rather than an array. Additionally, I want to continue to support array-style (with a deprecation message) for backward compatibility. So the sonarr content can either be a mapping or a sequence. The new schema would look like this:

sonarr:
  instance1:
    base_url: abc1
    api_key: xyz1
  instance2:
    base_url: abc2
    api_key: xyz2

I've spent hours googling and trying different solutions. Nothing seems to work. The approach I was trying was something like this:

public IEnumerable<T> LoadFromStream(TextReader stream, string configSection)
{
    var parser = new Parser(stream);
    parser.Consume<StreamStart>();
    parser.Consume<DocumentStart>();
    parser.Consume<MappingStart>();

    var validConfigs = new List<T>();
    while (parser.TryConsume<Scalar>(out var key))
    {
        if (key.Value != configSection)
        {
            parser.SkipThisAndNestedEvents();
            continue;
        }

        var evt = parser.Consume<NodeEvent>();
        var configs = evt switch
        {
            SequenceStart => _deserializer.Deserialize<Dictionary<string, T>>(parser)
                .Select(kvp =>
                {
                    kvp.Value.Name = kvp.Key;
                    return kvp.Value;
                })
                .ToList(),
            MappingStart => _deserializer.Deserialize<List<T>>(parser),
            _ => null
        };

        if (configs is not null)
        {
            ValidateConfigs(configSection, configs, validConfigs);
        }

        parser.SkipThisAndNestedEvents();
    }

    return validConfigs;
}

However, this won't work because the Consume and TryConsume methods eat the MappingStart / SequenceStart nodes, which makes it impossible to deserialize using List/Dictionary. I think to make this work I need a Consume that is more like a peek.

How should I go about handling this situation, or more generally, flexible schemas like this?