use cginc to write hlsl with VisualStudioHLSLTools

RGBCube_cginc.cginc

// RGBCube.shader
Shader "RGBCube" {
  SubShader{
	Pass{
	  CGPROGRAM
		#include "Assets\RBGCube\RGBCube_cginc.cginc"
		#pragma vertex vert 
		#pragma fragment frag 
	  ENDCG
	}
  }
}


// RGBCube_cginc.cginc
struct vertexOutput
{
    float4 pos : SV_POSITION;
    float4 col : TEXCOORD0; //Texture coordinates
};

vertexOutput vert(float4 vertexPos : POSITION)
{
    vertexOutput output;

    output.pos = UnityObjectToClipPos(vertexPos);
    output.col = vertexPos + float4(0.5, 0.5, 0.5, 0.0);
    return output;
}

float4 frag(vertexOutput input) : COLOR
{
    return input.col;
}

In RGBCube_cginc.cginc, If you write

#include {Unity Path}\Editor\Data\CGIncludes\UnityCG.cginc

IDE can autocomplete ``UnityObjectToClipPos`.