MemberNotNullWhen null tracking not working with generics #47667
Description
Version Used: 16.8.0 Preview 2.1 <TargetFramework>net5.0</TargetFramework><LangVersion>preview</LangVersion> <Nullable>enable</Nullable>
Steps to Reproduce:
Consider first the non generic example that works correctly:
class GetResult {
[MemberNotNullWhen(true, "Value")]
public bool OK { get; set; }
public Manager? Value { get; set; }
}
record Manager(int Age);
class Archive {
readonly Dictionary<string, Manager> Dict = new Dictionary<string, Manager>();
public GetResult this[string key]
=> Dict.TryGetValue(key, out var value)
? new GetResult {OK = true, Value = value}
: new GetResult {OK = false, Value = null};
}
public class C {
public void M() {
Archive archive = new Archive();
GetResult result = archive["John"];
if (!result.OK) return;
int age1 = result.Value.Age; // NO WARNING HERE - CORRECT
}
}Now almost the same code with generics:
class GetResult<T> {
[MemberNotNullWhen(true, "Value")]
public bool OK { get; set; }
public T? Value { get; init; }
}
record Manager(int Age);
class Archive {
readonly Dictionary<string, Manager> Dict = new Dictionary<string, Manager>();
public GetResult<Manager> this[string key]
=> Dict.TryGetValue(key, out var value)
? new GetResult<Manager> {OK = true, Value = value}
: new GetResult<Manager> {OK = false, Value = null};
}
public class C {
public void M() {
Archive archive = new Archive();
var result = archive["John"];
if (!result.OK) return;
int age1 = result.Value.Age; // WARNING HERE - Dereference of a possibly null reference
}
}Expected Behavior:
The second generic version do not give a warning when accessing result.Value (in the same way as first non generic version)
Actual Behavior:
The second generic version gives a "Dereference of a possibly null reference" warning when accessing result.Value