Unity-Technologies/UnityCsReference · error · Exception

More Assemblies in the list than delivered. Only filtering,

Error message

More Assemblies in the list than delivered. Only filtering, not adding extra assemblies

What it means

Thrown during the assembly-filtering phase of a build when an IFilterBuildAssemblies processor's OnFilterAssemblies returns an array longer than the one it received. The contract is strictly subtractive: processors may only remove assemblies, never add them. This guard catches processors that violate that invariant by returning more entries than they were given.

Source

Thrown at Editor/Mono/BuildPipeline/BuildPipelineInterfaces.cs:1416

        [RequiredByNativeCode]
        internal static string[] FilterAssembliesIncludedInBuild(BuildOptions buildOptions, string[] assemblies)
        {
            if (processors.filterBuildAssembliesProcessor == null)
            {
                return assemblies;
            }

            string[] startAssemblies = assemblies;
            string[] filteredAssemblies = assemblies;

            foreach (var filteredAssembly in processors.filterBuildAssembliesProcessor)
            {
                using var _ = new ScopeTraceProfileBlock($"{filteredAssembly.GetType().Name}.OnFilterAssemblies");
                int assemblyCount = filteredAssemblies.Length;
                filteredAssemblies = filteredAssembly.OnFilterAssemblies(buildOptions, filteredAssemblies);
                if (filteredAssemblies.Length > assemblyCount)
                {
                    throw new Exception("More Assemblies in the list than delivered. Only filtering, not adding extra assemblies");
                }
            }

            if (!Array.TrueForAll(filteredAssemblies, x => startAssemblies.Contains(x)))
            {
                throw new Exception("New Assembly names are in the list. Only filtering are allowed");
            }

            return filteredAssemblies;
        }

        [RequiredByNativeCode]
        internal static void CleanupBuildCallbacks()
        {
            processors.buildTargetProcessors = null;
            processors.buildPlayerProcessors = null;
            processors.buildPreprocessors = null;
            processors.buildPostprocessors = null;

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Ensure OnFilterAssemblies only ever returns a subset (or the same set) of the assemblies it receives — never a superset.
2. If you need to add assemblies, use a different mechanism such as IPreprocessBuildWithReport or asmdef references rather than the filter hook.
3. Audit any installed packages/plugins that implement IFilterBuildAssemblies and disable or fix the offending one.

Example fix

// before
public string[] OnFilterAssemblies(BuildOptions buildOptions, string[] assemblies)
{
    var list = new List<string>(assemblies);
    list.Add("MyExtraAssembly.dll"); // WRONG — only filtering is allowed
    return list.ToArray();
}

// after
public string[] OnFilterAssemblies(BuildOptions buildOptions, string[] assemblies)
{
    // Only remove assemblies, never add
    return assemblies.Where(a => !a.Contains("Test")).ToArray();
}

// Inside IFilterBuildAssemblies.OnFilterAssemblies:
public string[] OnFilterAssemblies(BuildOptions buildOptions, string[] assemblies)
{
    int inputCount = assemblies.Length;
    string[] filtered = DoMyFiltering(assemblies);
    // Postcondition: result must not be larger than input
    if (filtered.Length > inputCount)
        throw new InvalidOperationException(
            $"OnFilterAssemblies returned {filtered.Length} entries but received {inputCount}. Only removal is allowed.");
    return filtered;
}

When it happens

Trigger: An IFilterBuildAssemblies implementation whose OnFilterAssemblies returns an array with more elements than the input assemblies array — e.g., by concatenating additional assembly names or returning a superset.

Common situations: A custom build processor attempts to inject additional assemblies into the build via the filter hook instead of using the correct API, or a processor accidentally creates a new array that duplicates entries. Also occurs when a third-party plugin's IFilterBuildAssemblies implementation is buggy or incompatible with the Unity version.

Related errors

• New Assembly names are in the list. Only filtering are allow
• Scene path "{0}" contains invalid directory separators.
• The build target does not support build appending.
• The build cannot be appended.
• Non-development build cannot allow debugging. Either add the

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/f49bb5e15b3e244d. Report an issue: GitHub.