`CS8620` reported on non-null argument passed to extension method with non-nullable params collection parameter

[just-ero]

Full issue information + repro project:
https://github.com/just-ero/roslyn-issues-repros/tree/main/5.0.0/009_NullabilityWarning_ParamsExtension

Version

Note

Roslyn: 5.0.0-2.25412.5 (b0b21b6)
.NET SDK: 10.0.100-preview.7.25380.108

Visual Studio Code: 1.103.2
C# Extension: 2.89.19
C# Dev Kit Extension: 1.50.20

Steps to Reproduce

1. Add the following code wherever syntactically applicable:

   class C;
   
   static class E
   {
       extension(C)
       {
           static void Extension(params C[] values) { }
       }
   
       static void M()
       {
           C.Extension(new C());
       }
   }

2. Observe Argument of type 'C' cannot be used for parameter 'values' of type 'C[]' in 'void extension(C).Extension(params C[] values)' due to differences in the nullability of reference types.

Expected Behavior

The warning is not reported. The parameter expects non-nullable values and new C() is not nullable.

Actual Behavior

It is.

[just-ero]

Of note: this is not observed in normal extension methods, nor in non-extension static methods.

[RikkiGibson]

Will try to get this done today