abiosoft/colima · error

unexpected error during yaml node traversal: doc has multipl

Error message

unexpected error during yaml node traversal: doc has multiple children of len %d

What it means

encodeYAML (util/yamlutil/yaml.go:99) requires the node produced by the Marshal->Unmarshal roundtrip to have exactly one child; yaml.Marshal never emits multi-document output, so Content length != 1 is an unreachable internal invariant. Like errors 295/296's sibling checks, it exists to fail loudly rather than silently mis-apply a config value to the wrong node.

Source

Thrown at util/yamlutil/yaml.go:99

		// nil slices are converted to untyped nil to encode as `null` instead of `[]`.
		// this preserves nil vs empty slice distinction when the yaml is loaded back.
		if v := reflect.ValueOf(val); v.Kind() == reflect.Slice && v.IsNil() {
			val = nil
		}

		// lazy way, delegate node construction to the yaml library via a roundtrip.
		// no performance concern as only one file is being read
		b, err := yaml.Marshal(val)
		if err != nil {
			return nil, fmt.Errorf("unexpected error nested value encoding: %w", err)
		}
		var newNode yaml.Node
		if err := yaml.Unmarshal(b, &newNode); err != nil {
			return nil, fmt.Errorf("unexpected error during yaml node traversal: %w", err)
		}

		if l := len(newNode.Content); l != 1 {
			return nil, fmt.Errorf("unexpected error during yaml node traversal: doc has multiple children of len %d", l)
		}
		*node = *newNode.Content[0]
	}

	b, err := encode(root)
	if err != nil {
		return nil, fmt.Errorf("error encoding yaml file: %w", err)
	}

	return b, nil
}

func traverseConfig(parentKey string, s any, vals map[string]any) {
	typ := reflect.TypeOf(s)
	val := reflect.ValueOf(s)

	// everything else is a value, no nesting required
	if typ.Kind() != reflect.Struct {

View on GitHub (pinned to c3a5f9184d)

Solutions

1. Restore the stock gopkg.in/yaml.v3 dependency and rebuild
2. Verify `go version -m ./colima` shows the expected module versions
3. Report upstream with the reported length value for diagnosis

if err := util.Save(cfg, file); err != nil {
    if strings.Contains(err.Error(), "multiple children") {
        // unreachable invariant hit: report binary/library versions upstream
    }
    return err
}

When it happens

Trigger: Unreachable through normal input; would require a yaml.v3 implementation whose Unmarshal into a Node produces multiple document children for single-document input (vendored fork or corrupted library).

Common situations: Effectively none; theoretically a vendored/patched yaml.v3 diverging from upstream behavior.

Related errors

• unexpected error during yaml node traversal: %w
• embedded default config is invalid yaml: %w
• unexpected error during yaml decode: doc has multiple childr
• error traversing yaml node: %w
• error encoding yaml file: %w

AI-assisted analysis of abiosoft/colima@c3a5f9184d (2026-08-15). Data as JSON: /api/errors/41274b0a94f8950f. Report an issue: GitHub.