stride3d/stride · error · YamlException

Unexpected parsing event found

Error message

Unexpected parsing event found [{parsingEvent}]. Expecting Scalar, Mapping or Sequence

What it means

TagTypeSerializer.ReadYaml expects the next parsing event to be a NodeEvent (Scalar, MappingStart, or SequenceStart). If the peeked event is any other ParsingEvent (e.g. DocumentEnd, StreamEnd, or a collection end event), it throws this YamlException with the event's location.

Solutions

1. Ensure the YAML document actually contains a value (not just '---' or comments).
2. Validate the YAML structure with a standard parser before deserialization.
3. Check for stray '---'/'...' markers or unbalanced flow collections in the input.
4. Fix the deserialization call site so the reader starts at the beginning of the document.

Example fix

// before (file.yaml)
---
---
// after
key: value

// Ensure document has content before deserializing
if (!yamlText.TrimStart().TrimStart('-',' ').Trim().Any(char.IsLetterOrDigit))
    throw new InvalidDataException("YAML document contains no value (only markers/comments)");

try { return serializer.Deserialize(reader); } catch (YamlException ex) when (ex.Message.Contains("Unexpected parsing event")) { throw new InvalidDataException($"Malformed YAML at {ex.Start}: expected Scalar/Mapping/Sequence", ex); }

When it happens

Trigger: A YAML document whose structure ends unexpectedly where a node is required — e.g. a document that is just '---' with no content, trailing document markers, or a stream misaligned so a collection-end event is read as a node.

Common situations: YAML files containing only comments or a bare document start marker; concatenated/malformed multi-document streams; deserializing with the reader positioned incorrectly inside a nested structure.

Related errors

• Unable to parse input
• Multiple identifiable objects with the same id
• Unable to decode asset part reference
• Unable to deserialize reference
• Unable to find class from tag

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/55ba6a6700a8a512. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Serialization/Serializers/TagTypeSerializer.cs:68

namespace Stride.Core.Yaml.Serialization.Serializers
{
    internal class TagTypeSerializer : ChainedSerializer
    {
        public override object ReadYaml(ref ObjectContext objectContext)
        {
            var parsingEvent = objectContext.Reader.Peek<ParsingEvent>();
            // Can this happen here?
            if (parsingEvent == null)
            {
                // TODO check how to put a location in this case?
                throw new YamlException("Unable to parse input");
            }

            var node = parsingEvent as NodeEvent;
            if (node == null)
            {
                throw new YamlException(parsingEvent.Start, parsingEvent.End, $"Unexpected parsing event found [{parsingEvent}]. Expecting Scalar, Mapping or Sequence");
            }

            var type = objectContext.Descriptor != null ? objectContext.Descriptor.Type : null;

            // Tries to get a Type from the TagTypes
            Type typeFromTag = null;
            if (!string.IsNullOrEmpty(node.Tag))
            {
                bool remapped;
                typeFromTag = objectContext.SerializerContext.TypeFromTag(node.Tag, out remapped);
                if (typeFromTag == null)
                {
                    throw new YamlException(parsingEvent.Start, parsingEvent.End, $"Unable to resolve tag [{node.Tag}] to type from tag resolution or registered assemblies");
                }

                // Store the fact that remap has occured on this tag
                if (remapped)
                {

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