dotnet/wpf · error · XamlParseException

SR.ParserTooManyAssemblies

Error message

SR.ParserTooManyAssemblies

What it means

AssemblyInfoRecord's AssemblyId property throws XamlParseException(SR.ParserTooManyAssemblies) when an assembly ID exceeds 0x0FFF (4095). The BAML format reserves the top bits of the 16-bit assembly ID for flags, so more than ~4095 distinct assembly references cannot be encoded.

Solutions

1. Reduce the number of assemblies referenced from XAML (consolidate control libraries, remove unused xmlns mappings)
2. Split the UI into multiple independently compiled projects to cap per-BAML assembly references
3. Audit xmlns/namespace imports for accidental assembly pulls (e.g. clr-namespace mapping huge assemblies)
4. If genuinely needed, this is a BAML format limit — escalate to the WPF team

// track distinct assembly references during XAML compilation and fail early
if (assemblyIds.Count >= 0x0FFF)
    throw new InvalidOperationException("Too many assemblies referenced from XAML (limit 4095)");

try { CompileBaml(project); }
catch (XamlParseException ex) when (ex.Message.Contains("assemblies")) {
    log.Error("Reduce referenced assemblies in XAML below 4095"); throw;
}

When it happens

Trigger: Compiling BAML that references more than 4095 distinct assemblies — each unique assembly reference consumed during writing gets a sequential ID in AssemblyId.

Common situations: Huge XAML projects or merged markup referencing an enormous closure of assemblies (control libraries, plugins, generated code) hitting the 12-bit ID limit during build.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• Can't Assign to Known Type attributes
• Could not find prefix for type
• Found unexpected Xmlns BAML record
• NotImplementedException
• SR.AssemblyIdNegative

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/16401873408f427e. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/BamlRecords.cs:4349

            set
            {
                _flags[_typeIdLowSection] = (short)  (value & 0xff);
                _flags[_typeIdHighSection] = (short) ((value & 0xff00) >> 8);
            }
        }

        // Assembly id of the assembly where this type is defined.
        // NOTE:  This is always positive in BAML files, but can be set
        //        to -1 for known types when created programmatically.
        internal short AssemblyId
        {
            get { return _assemblyId; }
            set
            {
                // Make sure we don't intrude on the Flags portion of the assembly ID
                if (_assemblyId > 0x0FFF)
                {
                    throw new XamlParseException(SR.ParserTooManyAssemblies);
                }
                _assemblyId = value;
            }
        }

        // Fully qualified name of type, including namespace
        internal string TypeFullName
        {
            get { return _typeFullName; }
            set { _typeFullName = value; }
        }

        // Additional properties not stored in the baml stream

        internal override BamlRecordType RecordType
        {
            get { return BamlRecordType.TypeInfo; }
        }

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