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NullabilityInfoContext reporting incorrect nullability for ParameterInfo of generic types #92487
Description
Description
When it comes to generic types, it is not possible for the NullabilityInfoContext class to determine the nullability of members whose type is a generic parameter -- in such cases NullabilityInfoContext will fall back to reporting the members as being Nullable. This works fine for the cases of PropertyInfo and FieldInfo, however I found a case where the nullability of a ParameterInfo is reported erroneously as NotNull.
Reproduction Steps
Type type = typeof(MyPoco<string>);
var ctx = new NullabilityInfoContext();
// Property nullability -- works as expected
PropertyInfo prop = type.GetProperties()[0];
NullabilityInfo propNullability = ctx.Create(prop);
Console.WriteLine(propNullability.ReadState); // Nullable
// Parameter nullability -- ReadState & WriteState reported as NotNull
var param = type .GetConstructors()[0].GetParameters()[0];
var info = ctx.Create(param);
Console.WriteLine(info.ReadState); // NotNull
Console.WriteLine(info.WriteState); // NotNull
public class MyPoco<T>
{
public MyPoco(T value) => Value = value;
public T Value { get; }
}Expected behavior
Parameter nullability should be reported as Nullable, similar to the property.
Actual behavior
Reported as NotNull.
Regression?
No response
Known Workarounds
No response
Configuration
No response
Other information
Adding a notnull constraint makes nullability information being reported as expected:
var ctx = new NullabilityInfoContext();
Type type = typeof(MyPoco<string>);
PropertyInfo prop = type.GetProperties()[0];
NullabilityInfo propNullability = ctx.Create(prop);
Console.WriteLine(propNullability.ReadState); // NotNull
var param = typeof(MyPoco<string>).GetConstructors()[0].GetParameters()[0];
var info = ctx.Create(param);
Console.WriteLine(info.ReadState); // NotNull
Console.WriteLine(info.WriteState); // NotNull
public class MyPoco<T> where T : notnull
{
public MyPoco(T value) => Value = value;
public T Value { get; }
}
Activity
eiriktsarpalis commentedon Sep 22, 2023
Related to #1256
karakasa commentedon Sep 23, 2023
It's likely because
NullabilityInfoContext.CheckParameterMetadataTypedoesn't handle.ctorruntime/src/libraries/System.Private.CoreLib/src/System/Reflection/NullabilityInfoContext.cs
Line 87 in b3ef498
I have implemented a quick fix. Let me check if it works.
Improve nullability check for generic parameters in ctor
Improve nullability check for generic `.ctor` parameters (#92514)
Sync code (#1)