C# function to get extension methods from an assembly.

GetExtensionMethods.cs

// Adapted from https://stackoverflow.com/a/299526
static IEnumerable<MethodInfo> GetExtensionMethods(Assembly assembly, Type extendedType)
{
    return assembly
        .GetTypes()
        .Where(type => type.IsSealed && !type.IsGenericType && !type.IsNested)
        .SelectMany(type => type.GetMethods(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static))
        .Where(method => method.IsDefined(typeof(ExtensionAttribute), false) &&
                         method.GetParameters()[0].ParameterType == extendedType);
}