Missing nullability warnings in method group conversions caused by incorrect processing of [NotNullIfNotNull] annotation referencing parameters with type parameter types #49865
Description
Version Used:
Branch master (8 Dec 2020)
Latest commit 1e97fb9 by msftbot[bot]:
Merge pull request #49844 from davidwengier/RestoreInternalVersionAPI
Restore internal API used by VS for Mac
Steps to Reproduce:
Compile and run the following code
#nullable enable
using System;
using System.Diagnostics.CodeAnalysis;
class C
{
[return: NotNullIfNotNull("t")] static string? MethodGroup<T>(T t) => t?.ToString();
static Func<T, string> GetFunc<T>()
{
Func<T, string> func = MethodGroup;
return func;
}
static void Main()
{
Func<string?, string> func = C.GetFunc<string?>();
string res = func(null);
res.ToString();
}
}
Expected Behavior:
Warning for assignment Func<T, string> func = MethodGroup since return type of MethodGroup is explicitly annotated as returning a nullable type and there are no guarantees about nullability of input parameter T
Actual Behavior:
No warnings. The program crashes at runtime with a NullReferenceException
Notes
I believe this line
https://github.com/RikkiGibson/roslyn/blob/278127fac18b475171495cf209e1d117fce92fbd/src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol_ImplementationChecks.cs#L1271
Should be
if (notNullIfParameterNotNull.Contains(overrideParam.Name) && !baseParameters[i].TypeWithAnnotations.GetValueNullableAnnotation().IsAnnotated())
Currently it's
if (notNullIfParameterNotNull.Contains(overrideParam.Name) && !baseParameters[i].TypeWithAnnotations.NullableAnnotation.IsAnnotated())
Which means that not annotated unconstrained generic parameters that might be substituted with annotated types are considered not-nullable
/cc @RikkiGibson