stride3d/stride · error · YamlException

Duplicate %TAG directive.

Error message

Duplicate %TAG directive.

What it means

The YAML emitter rejects a %TAG directive that duplicates one already registered for the document. Each tag handle (e.g. !e! or !x!) may be declared only once in a document's tag directive list, so Emitter.AnalyzeTagDirective throws when AnalyzeTagDirectives sees a repeated handle and duplicates are not explicitly allowed.

Solutions

1. Remove the duplicate %TAG directive so each handle appears only once per document
2. Give the second directive a unique handle
3. If duplicates are intentional, pass allowDuplicates=true to the directive analysis path
4. Clear tagDirectives between documents (the emitter does this on document start)

Example fix

// before
var directives = new List<TagDirective> {
  new TagDirective(new VersionName("!e!"), "tag:example,2000:"),
  new TagDirective(new VersionName("!e!"), "tag:other:")
};
// after
var directives = new List<TagDirective> {
  new TagDirective(new VersionName("!e!"), "tag:example,2000:"),
  new TagDirective(new VersionName("!o!"), "tag:other:")
};

bool valid = directives.GroupBy(d => d.Handle.Value).All(g => g.Count() == 1);
if (!valid) throw new InvalidOperationException("Duplicate %TAG handle in document");

try { emitter.Emit(docStart); }
catch (YamlException ex) when (ex.Message.Contains("Duplicate %TAG")) { /* deduplicate directives and retry */ }

When it happens

Trigger: Calling emitter.Emit with a DocumentStart event whose TagDirectives collection contains two entries with the same handle, or emitting two documents' tag directives into the same list without clearing between documents.

Common situations: Hand-constructing YamlStream/Emitter event graphs where tag directives are appended programmatically; merging tag directive lists from multiple YAML documents; tools that copy %TAG headers from multiple source files into one output.

Related errors

• Unable to decode asset reference
• Unable to decode asset reference
• Unable to extract asset reference from object
• Unable to extract url reference from object
• Event handlers can't be added or removed after the…

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/4cdebdb6c578c644. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Emitter.cs:818

            isWhitespace = false;
            isIndentation = false;
        }

        /// <summary>
        /// Append a directive to the directives stack.
        /// </summary>
        private void AppendTagDirective(TagDirective value, bool allowDuplicates)
        {
            if (tagDirectives.Contains(value))
            {
                if (allowDuplicates)
                {
                    return;
                }
                else
                {
                    throw new YamlException("Duplicate %TAG directive.");
                }
            }
            else
            {
                tagDirectives.Add(value);
            }
        }

        /// <summary>
        /// Check if a %YAML directive is valid.
        /// </summary>
        private static void AnalyzeVersionDirective(VersionDirective versionDirective)
        {
            if (versionDirective.Version.Major != Constants.MajorVersion || versionDirective.Version.Minor != Constants.MinorVersion)
            {
                throw new YamlException("Incompatible %YAML directive");
            }
        }

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