stride3d/stride · error · SyntaxErrorException

While scanning a %YAML directive, did not find expected…

Error message

While scanning a %YAML directive, did not find expected version number.

What it means

Scanner.ScanVersionDirectiveValue finished reading a %YAML directive component but consumed zero digits, meaning the expected major or minor version number is missing. Since a %YAML directive requires 'major.minor', the scanner throws SyntaxErrorException.

Solutions

Write a complete version: '%YAML 1.1' (or 1.2).
Remove the %YAML directive entirely if version declaration is not needed.
Fix template placeholders so a literal version number is emitted.
Catch SyntaxErrorException and surface the mark/line for the user to fix the directive.

Example fix

// before (input.yaml)
%YAML 1.
---
doc: true

// after (input.yaml)
%YAML 1.1
---
doc: true

Defensive patterns

Strategy: validation

Validate before calling

// C#
var m = System.Text.RegularExpressions.Regex.Match(yamlText ?? "", @"^%YAML\s+\d+\.\d+\s*$", System.Text.RegularExpressions.RegexOptions.Multiline);
if (yamlText != null && yamlText.Contains("%YAML") && !m.Success)
    throw new FormatException("%YAML directive must be of the form '%YAML major.minor' (e.g. '%YAML 1.1').");

Try / catch

try { deserializer.Deserialize(reader, targetType); }
catch (SyntaxErrorException ex) { throw new YamlConfigException($"Incomplete %YAML version directive at line {ex.Start.Line}", ex); }

Prevention

Templates must substitute a literal version number, never placeholders.
Validate directive lines with a regex before deserializing user-supplied YAML.
Drop the %YAML directive if you don't need an explicit version.

When it happens

Trigger: Directives like '%YAML' alone, '%YAML .' or '%YAML 1.' (missing minor), or '%YAML x.y' where a non-digit appears where the version number must start.

Common situations: Truncated directive lines from failed edits; placeholders like '%YAML {version}' left by templates; files concatenated so the version digits ended up on the next line.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/984dd8f32dc148e0. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Scanner.cs:2293

            while (analyzer.IsDigit())
            {
                // Check if the number is too long.

                if (++length > MaxVersionNumberLength)
                {
                    throw new SyntaxErrorException(start, mark, "While scanning a %YAML directive, find extremely long version number.");
                }

                value = value*10 + analyzer.AsDigit();

                Skip();
            }

            // Check if the number was present.

            if (length == 0)
            {
                throw new SyntaxErrorException(start, mark, "While scanning a %YAML directive, did not find expected version number.");
            }

            return value;
        }

        /// <summary>
        /// Check if a simple key may start at the current position and add it if
        /// needed.
        /// </summary>
        private void SaveSimpleKey()
        {
            // A simple key is required at the current position if the scanner is in
            // the block context and the current column coincides with the indentation
            // level.


            bool isRequired = (flowLevel == 0 && indent == mark.Column);

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