Shader error in 'MC/Toon': profile specifier "nointerpolation" not allowed on non-function (978790)

So I do this, which works in CG and instead of a deadly error I get something informative but I can't figure out if it's saying that nointerpolation is now accepted as a way to flatten polygons or if it's just some generic message.
So if nointerpolation is now part of surface shader, how do we use it?

Code (CSharp):

1.         struct Input
2.         {
3.             float2 uv_texcoord;
4.             nointerpolation float3 worldNormal;
5.             INTERNAL_DATA
6.             float3 worldPos;
7.         };
8.  
9.         struct SurfaceOutputCustomLightingCustom
10.         {
11.             nointerpolation fixed3 Albedo;
12.             nointerpolation fixed3 Normal;
13.             half3 Emission;
14.             half Metallic;
15.             half Smoothness;
16.             half Occlusion;
17.             fixed Alpha;
18.             Input SurfInput;
19.             UnityGIInput GIData;
20.         };

spits out

Code (CSharp):

1.  
2. Shader error in 'MC/Toon': profile specifier "nointerpolation" not allowed on non-function "worldNormal" at line 60 (on d3d9)
3.