The Conditional attribute is not valid on 'function' because it is a constructor, destructor, operator, or explicit interface implementation
Conditional cannot be applied to the specified methods.
For example, you cannot use some attributes on an explicit interface definition. The following sample generates CS0577:
// CS0577.cs
// compile with: /target:library
interface I
{
void m();
}
public class MyClass : I
{
[System.Diagnostics.Conditional("a")] // CS0577
void I.m() {}
}