Support [NotNullIfNotNull(string)] on indexers #37238
Description
Relates to #35816
See NullableWalker.VisitArguments, which gets the relevant attribute information from ReturnNotNullIfParameterNotNull for method symbols, but we don't have the equivalent for property/indexer symbols.
The NotNullIfNotNull attribute can target a property/indexer.
When we implement this, we should also test the enforcement within the body of the getter.
This also affects extension property scenarios, since these are properties that now have a parameter (the extension parameter) and should also honor this attribute.
[Fact]
public void TODO2()
{
var src = """
#nullable enable
object? oNull = null;
new C()[oNull].ToString(); // correct warning
object oNotNull = new object();
new C()[oNotNull].ToString(); // should not warn, but does
class C
{
[property: System.Diagnostics.CodeAnalysis.NotNullIfNotNull(nameof(o))]
public object? this[object? o] { get => throw null!; }
}
""";
var comp = CreateCompilation(src, targetFramework: TargetFramework.Net90);
comp.VerifyEmitDiagnostics(
// (4,1): warning CS8602: Dereference of a possibly null reference.
// new C()[oNull].ToString();
Diagnostic(ErrorCode.WRN_NullReferenceReceiver, "new C()[oNull]").WithLocation(4, 1),
// (7,1): warning CS8602: Dereference of a possibly null reference.
// new C()[oNotNull].ToString();
Diagnostic(ErrorCode.WRN_NullReferenceReceiver, "new C()[oNotNull]").WithLocation(7, 1));
}
Note: This issue is referenced in source