Unity-Technologies/UnityCsReference · error · NotImplementedException

Use of reference assemblies is always enabled

Error message

Use of reference assemblies is always enabled

What it means

ScriptCompilerOptions.EmitReferenceAssembly is marked [Obsolete(..., true)] and both getter and setter throw NotImplementedException unconditionally — reference assemblies are now always enabled and the property is hard-banned. Any read or write of it throws at runtime (and is a compile error for new code).

Source

Thrown at Editor/Mono/Scripting/ScriptCompilation/CompilationPipeline.cs:46

    [Flags]
    public enum RequestScriptCompilationOptions
    {
        None,
        CleanBuildCache
    }

    public class ScriptCompilerOptions
    {
        public string RoslynAnalyzerRulesetPath { get; set; }
        public string[] RoslynAnalyzerDllPaths { get; set; }
        public string[] RoslynAdditionalFilePaths { get; set; }
        public string AnalyzerConfigPath {get; set;}
        public bool AllowUnsafeCode { get; set; }

        [Obsolete("Use of reference assemblies is always enabled", true)]
        public bool EmitReferenceAssembly
        {
            get { throw new NotImplementedException("Use of reference assemblies is always enabled"); }
            set { throw new NotImplementedException("Use of reference assemblies is always enabled"); }
        }

        internal bool UseDeterministicCompilation { get; set; }
        public string[] AdditionalCompilerArguments { get; set; }
        public CodeOptimization CodeOptimization { get; set; }
        public ApiCompatibilityLevel ApiCompatibilityLevel { get; set; }
        public EditorAssembliesCompatibilityLevel EditorAssembliesCompatibilityLevel { get; set; }
        public string[] ResponseFiles { get; set; }
        public string LanguageVersion { get; internal set; } // Requires a refresh sent to the Code Editor package if made public

        public ScriptCompilerOptions()
        {
            AllowUnsafeCode = false;
            ApiCompatibilityLevel = ApiCompatibilityLevel.NET_Unity_4_8;
            EditorAssembliesCompatibilityLevel = EditorAssembliesCompatibilityLevel.Default;
            ResponseFiles = Array.Empty<string>();
            RoslynAnalyzerDllPaths = Array.Empty<string>();

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Remove all uses of EmitReferenceAssembly from your code; reference assemblies are always on.
2. Upgrade packages that still reference the obsolete property.

Example fix

// before
options.EmitReferenceAssembly = true;
// after
// (remove the line; reference assemblies are always enabled)

// There is nothing to validate: the property always throws.
// Remove the call site entirely; reference assemblies are mandatory.

When it happens

Trigger: Reading or writing ScriptCompilerOptions.EmitReferenceAssembly (the property always throws NotImplementedException).

Common situations: Legacy code or a third-party package that toggled reference assembly emission before it became mandatory.

Related errors

• AA is not supported on GUIViews
• GetRenderersFilteringResults(ReadOnlySpan<int>) is obsolete.
• GetRenderersHiddenResultBits(ReadOnlySpan<int>) is obsolete.
• EditorApplication.OpenScene() cannot be called when in the U
• CompileCSharp is no longer supported. Use UnityEditor.Compil

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/35a34b98bb241de0. Report an issue: GitHub.