Why this shader wont compile

Unity Engine
1

I don’t know why this shader wont compile. The error is in line where I try to set world position in posWorld.

Shader "Custom/Phong" {
	Properties {

	}
	SubShader {
		pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			
			struct Input
			{
				float4 pos : POSITION;
				float3 n : NORMAL;
				float2 tex : TEXCOORD0;
			};
			
			struct Output
			{
				float4 pos : SV_POSITION;
				float4 posWorld : TEXCOORD0;
			};

			Output vert(Input i) 
			{
				Output o;
				
				o.pos = mul(UNITY_MATRIX_MVP, i.pos);
				o.posWorld = mul(_Object2World, i.pos):  // this line wont compile
				
				return o;
			}

			float4 frag(Output i) : COLOR 
			{
				return float4(1.0, 1.0, 1.0, 1.0);
			}

			ENDCG
		}
	} 
	FallBack "Diffuse"
}
2

It looks like that I had to put Tags {“LightMode” = “ForwardBase”}, trough I don’t know why.