nullability of value parameter in properties

[dlech]

Version Used: master (23 September 2019) via https://sharplab.io

Steps to Reproduce:

#nullable enable

using System;
using System.Diagnostics.CodeAnalysis;

public class C {
    string? Getter() {
        return null;
    }
    
    void Setter(string s) {
    }
    
    [DisallowNull]
    public string? Property {
        get => Getter();
        set => Setter(value); // get unexpected warning here
    }
    
    public void Test() {
        Property = ""; // no warning here as expected
        Property = null; // get warning here as expected
        Setter(Property); // get warning here as expected
    }
}

Expected Behavior: Given a property with the DisallowNull attribute it should mean that the return value can be null but value parameter of the setter cannot be null.

Actual Behavior: The code analysis gets this right when assigning to a property, but not in the property declaration.

[gafter]

I believe this is by design. It was not intended that [DisallowNull] have an effect on the type of the parameter inside the method.

[dlech]

This gives an unexpected warning as well

#nullable enable

using System;
using System.Diagnostics.CodeAnalysis;

public class C {
    string? Getter() {
        return null;
    }
    
    void Setter(string s) {
    }
    
    [MaybeNull]
    public string Property {
        get => Getter(); // get unexpected warning here
        set => Setter(value);
    }
    
    public void Test() {
        Property = ""; // no warning here as expected
        Property = null; // get warning here as expected
        Setter(Property); // get warning here as expected
    }
}

So it doesn't seem possible to have a property with different nullability for the getter and setter when the getter and setter are expression bodied.

[agocke]

Moving to csharplang because this is by-design for the compiler