var compilation = CreateCompilation(new[] { source }, options: WithNonNullTypesTrue());
compilation.VerifyTypes();
compilation.VerifyDiagnostics(
// (18,25): warning CS8621: Nullability of reference types in return type of 'string[]? C.NullableReturnMethod(string[] x)' doesn't match the target delegate 'MyDelegate'.
// (24,33): warning CS8622: Nullability of reference types in type of parameter 'x' of 'string[] C.Method(string[] x)' doesn't match the target delegate 'MyNullableDelegate'.
// (26,33): warning CS8622: Nullability of reference types in type of parameter 'x' of 'string[]? C.NullableReturnMethod(string[] x)' doesn't match the target delegate 'MyNullableDelegate'.
// (24,13): warning CS8622: Nullability of reference types in type of parameter 't' of 'void E.F<string>(string t)' doesn't match the target delegate 'D1<string?>'.
// (21,29): warning CS8622: Nullability of reference types in type of parameter 't' of 'void E.F<string>(string t)' doesn't match the target delegate 'D1<string?>'.