dotnet/machinelearning · error · ArgumentException

Did not find access modifier (Parameter 'constructorInfo')

Error message

Did not find access modifier (Parameter 'constructorInfo')

What it means

The Accessmodifier extension on ConstructorInfo mirrors the MethodInfo version: it classifies constructor visibility into the AccessModifier enum and throws ArgumentException('Did not find access modifier', nameof(constructorInfo)) if no visibility flag matches. ComponentCatalog invokes it when enumerating registrable constructors.

Source

Thrown at src/Microsoft.ML.Core/ComponentModel/ComponentCatalog.cs:50

            return AccessModifier.Public;
        throw new ArgumentException("Did not find access modifier", nameof(methodInfo));
    }

    internal static AccessModifier Accessmodifier(this ConstructorInfo constructorInfo)
    {
        if (constructorInfo.IsFamilyAndAssembly)
            return AccessModifier.PrivateProtected;
        if (constructorInfo.IsPrivate)
            return AccessModifier.Private;
        if (constructorInfo.IsFamily)
            return AccessModifier.Protected;
        if (constructorInfo.IsFamilyOrAssembly)
            return AccessModifier.ProtectedInternal;
        if (constructorInfo.IsAssembly)
            return AccessModifier.Internal;
        if (constructorInfo.IsPublic)
            return AccessModifier.Public;
        throw new ArgumentException("Did not find access modifier", nameof(constructorInfo));
    }

    internal enum AccessModifier
    {
        PrivateProtected,
        Private,
        Protected,
        ProtectedInternal,
        Internal,
        Public
    }
}

/// <summary>
/// This catalogs instantiable components (aka, loadable classes). Components are registered via
/// a descendant of <see cref="LoadableClassAttributeBase"/>, identifying the names and signature types under which the component
/// type should be registered. Signatures are delegate types that return void and specify that parameter
/// types for component instantiation. Each component may also specify an "arguments object" that should

View on GitHub (pinned to 7b76e69cf9)

Solutions

1. Only register statically compiled, normal CLR types with ComponentCatalog.
2. Check the target constructor's visibility flags via reflection before registration and skip non-standard ones.
3. Catch ArgumentException during registration and log/skip the offending type.
4. Rebuild the component assembly if its metadata appears corrupted.

Example fix

// before
catalog.RegisterComponent(typeof(DynamicProxy));
// after
var ctors = typeof(DynamicProxy).GetConstructors(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
if (ctors.All(c => c.IsPublic || c.IsPrivate || c.IsFamily || c.IsAssembly || c.IsFamilyOrAssembly))
    catalog.RegisterComponent(typeof(DynamicProxy));

var c = typeof(MyComponent).GetConstructor(new[]{ typeof(MLContext) });
bool classifiable = c.IsPublic || c.IsPrivate || c.IsFamily ||
    c.IsAssembly || c.IsFamilyOrAssembly || c.IsFamilyAndAssembly;
if (!classifiable) throw new InvalidOperationException("Constructor visibility non-standard");

static bool HasStandardCtorVisibility(ConstructorInfo c) =>
    c.IsPublic || c.IsPrivate || c.IsFamily ||
    c.IsAssembly || c.IsFamilyOrAssembly || c.IsFamilyAndAssembly;

try
{
    catalog.RegisterComponent(type);
}
catch (ArgumentException ex) when (ex.ParamName == "constructorInfo")
{
    logger.LogWarning($"Skipped {type}: non-standard constructor visibility");
}

When it happens

Trigger: ComponentCatalog enumerating constructors of a registered type and encountering a ConstructorInfo with none of the standard visibility flags — typically only from dynamically emitted constructors or non-standard compiler output.

Common situations: Registering types from Reflection.Emit-generated assemblies; duplicate/corrupted assembly versions where the reflected constructor metadata is malformed.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Did not find access modifier (Parameter 'methodInfo')
• Type IPredictionTransformer not implemented by provided type
• nameof(values)
• The provided model file {filePath} doesn't exist.
• Start must be called on a ModelLoader before it can be used.

AI-assisted analysis of dotnet/machinelearning@7b76e69cf9 (2026-09-11). Data as JSON: /api/errors/10c5b1e9f68ec04c. Report an issue: GitHub.