Annotate query with nullable reference types

[smitpatel]

Changing the world one file at time!

Part of #19007

[smitpatel]

Looking for early feedback if people want to have this done something differently, before I start changing provider code.

[roji]

Looks great, not much work for so many files :)

[roji]

_materializers can just be be nullable.

BTW I've just annotated NonCapturingLazyInitializer as part of #23133, you can annotate LazyInitializer in the exact same way (do we really need two?)

[smitpatel]

LazyInitializer comes from above. Make it just nullable infers the generic type as nullable even though the method definition in the source uses ref T?

[roji]

I think that if in LazyInitializer you annotate TValue without question mark (#23126 (comment)), and you annotate _materializers as nullable here, it should be fine.

[smitpatel]

But LazyInitializer is not mine.
https://github.com/dotnet/runtime/blob/master/src/libraries/System.Private.CoreLib/src/System/Threading/LazyInitializer.cs

[roji]

Ah sorry, missed that. In any case, the following does seem to work (with _materializers being nullable):

private ConcurrentDictionary<IEntityType, Func<MaterializationContext, object>> Materializers
    => LazyInitializer.EnsureInitialized(
        ref _materializers,
        () => new ConcurrentDictionary<IEntityType, Func<MaterializationContext, object>>())!;

So there's a bang at the end of the expression (because the compiler doesn't know EnsureInitialized sets to non-null), but the annotation of _materializers is more correct, i.e. in case someone accesses it directly.

[smitpatel]

@roji volunteered to follow-up with runtime team why there is mismatch here.
Specifying generic type arg to be non-null does not fix issue either.
But putting bang as in code or in above example make it work.

[roji]

The actual reason is simply that we're currently targeting netstandard2.1, where LazyInitializer isn't yet null-annotated. In net5.0 it is and the bang is no longer necessary.

Will add a TODO-NULLABLE as a reminder for this.