Feedback Array in vertex output not support for metal api?

I'm working on 2018.3.10f1 and I have such a vertex output struct within an array field which works well on dx and opengl es3 platform:

Code (csharp):

1.  
2. struct v2f
3. {
4.     FLOAT4 vertex : SV_POSITION;
5.     FLOAT4 color : COLOR;
6.     FLOAT2 texcoord : TEXCOORD0;
7.     FLOAT4 light[4] : TEXCOORD1;
8. };
9.  

However, I got a wrong result on mac with metal api selected. I checked the generated shader code which only contains one of the array elements such as:

Code (csharp):

1.  
2. struct Mtl_FragmentIn
3. {
4.     float4 COLOR0 [[ user(COLOR0) ]] ;
5.     float2 TEXCOORD0 [[ user(TEXCOORD0) ]] ;
6.     float4 TEXCOORD1 [[ user(TEXCOORD1) ]] ;
7. };
8.  

If I expand the field manually such as:

Code (csharp):

1.  
2. struct v2f
3. {
4.     FLOAT4 vertex : SV_POSITION;
5.     FLOAT4 color : COLOR;
6.     FLOAT2 texcoord : TEXCOORD0;
7.     FLOAT4 light_0 : TEXCOORD1;
8.     FLOAT4 light_1 : TEXCOORD2;
9.     FLOAT4 light_2 : TEXCOORD3;
10.     FLOAT4 light_3 : TEXCOORD4;
11. };
12.  

It could generate the right code:

Code (csharp):

1.  
2. struct Mtl_FragmentIn
3. {
4.     float4 COLOR0 [[ user(COLOR0) ]] ;
5.     float2 TEXCOORD0 [[ user(TEXCOORD0) ]] ;
6.     float4 TEXCOORD1 [[ user(TEXCOORD1) ]] ;
7.     float4 TEXCOORD2 [[ user(TEXCOORD2) ]] ;
8.     float4 TEXCOORD3 [[ user(TEXCOORD3) ]] ;
9.     float4 TEXCOORD4 [[ user(TEXCOORD4) ]] ;
10. };
11.  

Is this by design that array field in vertex output won't be auto expand when targeting metal api? Or could this be a bug?

 

Here is the bug report link
https://fogbugz.unity3d.com/default.asp?1155513_v23aibhp35vlm2cd