'typeof(T).FullName' is never null

[sharwell]

Version Used: 3.7, targeting netcoreapp3.1

Steps to Reproduce:

#nullable enable

class C
{
  string TypeName => typeof(C).FullName;
}

Expected Behavior:

No warning is reported for the expression returned from TypeName.

Actual Behavior:

warning CS8603: Possible null reference return.

Additional Information:

While the FullName property can return null in some cases, it cannot return null for the syntax seen here. There is no way to annotate the property as having a non-null value conditioned on language-specific syntax producing the Type instance.

[tannergooding]

There are lots of APIs in .NET, especially in the reflection/metadata namespaces that will never return null except for some weird edge case (generally around dynamically created types).

Is this one really that special in comparison?

[jaredpar]

Moving to csharplang as this is really a language design topic. Essentially the question comes down to whether or not we want the language to override the annotations of the runtime library in specific contexts like typeof.

[Joe4evr]

Asked about this some time ago myself. Stephen gave a good explanation: https://github.com/dotnet/runtime/issues/31558#issuecomment-557932606

[jnm2]

This would be addressed by a proposal to make typeof(C).FullName a constant in that code sample (#8505).