Open issue: nullability analysis of collection expressions about csharplang

[CyrusNajmabadi]

As a user, either warnings would be fine. I'm getting a NRT warning, and it's effectively telling me that object! and object? are going to be a problem. That's literally all that matters, and the exact verbiage isn't really going to matter to me :)

[TahirAhmadov]

How about a combination of option 1 with another language rule - if it has IEnumerable<T> and void Add(T? item) { ... }, produce a new NRT warning about inconsistent surface area?

class C<T> : IEnumerable<T>
{
  ...
  public void Add(T? t) { }
}
C<object> c1 = [maybeNull]; // 2 warnings: the iteration type is `object!` but the element is maybe-null `object`, 
// and `Add` is incompatible with `IEnumerable<>`

[jcouv]

Discussed in LDM 11/15. In short, we're going with option 1 (check conversion of elements to iteration type).

[333fred]

Discussed in LDM on https://github.com/dotnet/csharplang/blob/main/meetings/2023/LDM-2023-11-15.md#nullability-analysis-of-collection-expressions.