Reproduction steps:
1. Open attached project.
2. Select "RainSplash_Bug" shader.
3. Select "Custom > OpenGLCore" in a compiled code drop down menu.
4. Click "Compile and show code".
5. Notice the error in a console window:
* Shader compiler: internal error compiling shader snippet type=0 platform=15: Protocol error - failed to read correct magic number
UnityEditor.DockArea:OnGUI()

Workaround:
* Check "RainSplash" shader in the project. It is remade using vertex instead of fragment shader for some calculations.

Note:
* May be related to case 768041, but "Skip unused shader_features" doesn't impact the result of case 802916.