"Can't open include file "HLSLSupport.cginc""

I’m getting this error in all of my pro shaders that include “HLSLSupport.cginc”, but I can’t find any information on this error, as if nobody has ever gotten it before. One of my projects has this error, but another one of mine, also created before I used Unity Pro, compiles these shaders just fine. I’m guessing this project isn’t finding HLSLSupport.cginc, but I have no idea where to start in fixing this. If this file resides somewhere in the system or in the project, I have no idea where. Does anybody know how to fix this?

the one way to fix this is to give this file to shader compiler
by default (for Windows) all ‘…inc’ files are stored in folder

[program files folder]\Unity\Editor\Data\CGIncludes\

so try to locate it there and if there’s no this file, find one from correct installation and put it there

One (stupid) pitfall I found about includes in shader is

If one of the include fails, it fails all built-in also. (Thus those misleading error message about built-in cginc missing, which is outside user’s responsibility)

For example, if you have shader “Assets/Shaders/a.shader” which has CGINCLUDE, and custom includes that says #include "Extra/ColorUtil.cginc" (expects Assets/Shaders/Extra/ColorUtil.cginc) and you dont have it. You get complain about built-in!
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Credit this finding to this blog (Japanese)