Stripping commonly unused shader variants in Unity's built-in render pipeline

ShaderStripper.cs

//#define SHADER_COMPILATION_LOGGING
//#define SKIP_SHADER_COMPILATION

using System.Collections.Generic;
using UnityEditor.Build;
using UnityEditor.Rendering;
using UnityEngine;
using UnityEngine.Rendering;

public class ShaderStripper : IPreprocessShaders
{
	private const string LOG_FILE_PATH = "Library/Shader Compilation Results.txt";

	private static readonly ShaderKeyword[] SKIPPED_VARIANTS = new ShaderKeyword[]
	{
		new ShaderKeyword( "DIRECTIONAL_COOKIE" ),
		new ShaderKeyword( "POINT_COOKIE" ),
		//new ShaderKeyword( "LIGHTPROBE_SH" ), // Apparently used by lightmapping, as well
	};

	public int callbackOrder { get { return 0; } }

	public void OnProcessShader( Shader shader, ShaderSnippetData snippet, IList<ShaderCompilerData> data )
	{
		// Don't strip essential shaders
		string shaderName = shader.name;
		if( shaderName.StartsWith( "Hidden/" ) || shaderName.StartsWith( "Unlit/" ) || shaderName.StartsWith( "Legacy Shaders/" ) || shaderName.StartsWith( "Particles/" ) )
			return;

#if SHADER_COMPILATION_LOGGING
		System.IO.File.AppendAllText( LOG_FILE_PATH, "\n\n\n\n===== " + shader.name + " " + snippet.passName + " " + snippet.passType + " " + snippet.shaderType + "\n" );
#endif

		if( snippet.passType == PassType.Deferred || snippet.passType == PassType.LightPrePassBase || snippet.passType == PassType.LightPrePassFinal || snippet.passType == PassType.ScriptableRenderPipeline || snippet.passType == PassType.ScriptableRenderPipelineDefaultUnlit )
		{
#if SHADER_COMPILATION_LOGGING
			System.IO.File.AppendAllText( LOG_FILE_PATH, "Skipped shader variant because it uses SRP or Deferred shading\n" );
#endif

			data.Clear();
		}

		for( int i = data.Count - 1; i >= 0; --i )
		{
			bool shouldSkipShaderVariant = false;
			foreach( ShaderKeyword keywordToSkip in SKIPPED_VARIANTS )
			{
				if( data[i].shaderKeywordSet.IsEnabled( keywordToSkip ) )
				{
					shouldSkipShaderVariant = true;
					break;
				}
			}

			if( shouldSkipShaderVariant )
			{
				data.RemoveAt( i );
				continue;
			}

#if SHADER_COMPILATION_LOGGING
			string keywords = "";
			foreach( ShaderKeyword keyword in data[i].shaderKeywordSet.GetShaderKeywords() )
				keywords += keyword.GetKeywordName() + " ";

			if( keywords.Length == 0 )
				keywords = "No keywords defined";

			System.IO.File.AppendAllText( LOG_FILE_PATH, "- " + keywords + "\n" );
#endif
		}

#if SKIP_SHADER_COMPILATION
		for( int i = data.Count - 1; i >= 0; --i )
			data.Clear();
#endif
	}
}