stride3d/stride · error · SyntaxErrorException

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

Error message

While scanning a %TAG directive, did not find expected whitespace or line break.

What it means

Thrown by the YAML Scanner when, after scanning the tag URI prefix of a %TAG directive, the next character is not a whitespace, line break, or end of input. The directive must terminate with whitespace or a break; trailing garbage (like a second token glued to the prefix) is rejected.

Solutions

Ensure the tag prefix is followed by whitespace or a newline before anything else on the line.
Remove any stray characters directly after the prefix URI.
Move subsequent content onto its own line after the directive.
Pre-validate the YAML (yamllint) in CI so malformed directives are caught before parsing.

Example fix

// before
%TAG !e! tag:example.com,2000:extra
// after
%TAG !e! tag:example.com,2000:

Defensive patterns

Strategy: validation

Validate before calling

// %TAG line must end after the prefix (whitespace/linebreak only)
bool TagDirectiveLineTerminates(string line) =>
    !line.StartsWith("%TAG") ||
    System.Text.RegularExpressions.Regex.IsMatch(line, "^%TAG\\s+\\S+\\s+\\S+\\s*$");

Try / catch

try
{
    var obj = Deserializer.FromFile(path);
}
catch (SyntaxErrorException ex)
{
    Log.Error(ex, "Trailing garbage after %TAG prefix at line {Line}", ex.Start.Line);
    throw new YamlConfigException("%TAG prefix must be followed by whitespace or line break", ex);
}

Prevention

Put each %TAG directive on its own line, ending right after the prefix
Watch for trailing punctuation (',', ')') introduced by copy-paste
Run yamllint in CI on all YAML artifacts

When it happens

Trigger: Parsing YAML with a %TAG directive whose prefix is immediately followed by another non-space token, e.g. '%TAG !e! tag:example.com,2000:extra-token' with no separating whitespace, or characters like ',' or ')' directly after the prefix.

Common situations: Multiple tokens merged by whitespace stripping; trailing punctuation from surrounding text (e.g. prefix pasted with a trailing comma); typos concatenating the prefix with the next directive or document content.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/30460ac91475b429. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Scanner.cs:2098

            // Expect a whitespace.

            if (!analyzer.IsBlank())
            {
                throw new SyntaxErrorException(start, mark, "While scanning a %TAG directive, did not find expected whitespace.");
            }

            SkipWhitespaces();

            // Scan a prefix.

            string prefix = ScanTagUri(null, start);

            // Expect a whitespace or line break.

            if (!analyzer.IsBlankOrBreakOrZero())
            {
                throw new SyntaxErrorException(start, mark, "While scanning a %TAG directive, did not find expected whitespace or line break.");
            }

            return new TagDirective(handle, prefix, start, start);
        }

        /// <summary>
        /// Scan a tag.
        /// </summary>
        private string ScanTagUri(string head, Mark start)
        {
            StringBuilder tag = new StringBuilder();
            if (head != null && head.Length > 1)
            {
                tag.Append(head.Substring(1));
            }

            // Scan the tag.

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