Reporting "field is uninitialized" for constructor that throws an exception

[cston]

Reports: (5,14): warning CS8618: Non-nullable field '_f' is uninitialized.

using System;
class C
{
    private object _f;
    internal C()
    {
        throw new NotImplementedException();
    }
}

[gafter]

In unreachable code every variable is definitely not null.

[AlexanderTaeschner]

Yes, but in this case, the call to this default constructor will not create a class with an uninitialized field either, since the constructor call will fail! The use case would be a class with a second constructor, e.g. public C(object f) => _f = f; which guarantees the initialization of the internal field.

[gafter]

@AlexanderTaeschner Agreed. That is why the rule I stated works for this case (the end of the constructor is not reachable).

[jcouv]

This issue still exists in recent 16.1 branch:

        [Fact]
        public void Test()
        {
            var comp = CreateCompilation(@"
using System;
class C
{
    private object _f;
    internal C()
    {
        throw new NotImplementedException();
    }
}", options: WithNonNullTypesTrue());
            comp.VerifyDiagnostics(
                // (5,20): warning CS0169: The field 'C._f' is never used
                //     private object _f;
                Diagnostic(ErrorCode.WRN_UnreferencedField, "_f").WithArguments("C._f").WithLocation(5, 20),
                // (6,14): warning CS8618: Non-nullable field '_f' is uninitialized.
                //     internal C()
                Diagnostic(ErrorCode.WRN_UninitializedNonNullableField, "C").WithArguments("field", "_f").WithLocation(6, 14)
                );
        }