Incorrect nullability warnings on increment/decrement operators on nullable variables

[TessenR]

Version Used:

Branch master (19 Dec 2020)
Latest commit 80e9227 by msftbot[bot]:
Merge pull request #50073 from dotnet/merges/release/dev16.9-to-master

Merge release/dev16.9 to master

Steps to Reproduce:

#nullable enable
class C
{
  void Test(C? c)
  {
    c = new C();
    c++;
  }

  public static C? operator ++(C? c) => c;
}

Expected Behavior: No warnings. The variable c allows null values, the operator's parameter allows null values. There's nothing to warn about.

Actual Behavior: warning CS8601: Possible null reference assignment. is repoted for c++

Notes Note that if you remove the assignment c = new C() the warning disappears. It looks like Roslyn uses the actual nullability state of the variable c to determine allowed nullability instead of its annotation

[jcouv]

Assigned to @RikkiGibson for load balancing. Thanks