Cross compiler crashing with custom expressions

This looks like a bug with shader pipeline compilation and custom expressions.

Create the material shown in attachments, assign to mesh. set lighting to movable (to ensure the material is rendered via the depthonly pipeline.

ShaderCompileWorker-Core.dll!FOutputDeviceWindowsError::Serialize() [d:\work\perforce\streams\devmobile\engine\source\runtime\core\private\windows\windowsplatformoutputdevices.cpp:120]
ShaderCompileWorker-Core.dll!FOutputDevice::Logf__VA() [d:\work\perforce\streams\devmobile\engine\source\runtime\core\private\misc\outputdevice.cpp:70]
ShaderCompileWorker-Core.dll!FDebug::AssertFailed() [d:\work\perforce\streams\devmobile\engine\source\runtime\core\private\misc\assertionmacros.cpp:349]
ShaderCompileWorker-ShaderCompilerCommon.dll!CrossCompiler::AST::FParameterDeclarator::CreateFromDeclaratorList() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslast.cpp:1000]
ShaderCompileWorker-ShaderCompilerCommon.dll!CrossCompiler::ParseFunctionParameterDeclaration() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslparser.cpp:912]
ShaderCompileWorker-ShaderCompilerCommon.dll!CrossCompiler::ParseFunctionDeclarator() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslparser.cpp:975]
ShaderCompileWorker-ShaderCompilerCommon.dll!CrossCompiler::ParseFunctionDeclaration() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslparser.cpp:1050]
ShaderCompileWorker-ShaderCompilerCommon.dll!CrossCompiler::TryTranslationUnit() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslparser.cpp:1693]
ShaderCompileWorker-ShaderCompilerCommon.dll!CrossCompiler::Parser::Parse() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslparser.cpp:1782]
ShaderCompileWorker-ShaderCompilerCommon.dll!CrossCompiler::Parser::Parse() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslparser.cpp:1822]
ShaderCompileWorker-ShaderCompilerCommon.dll!RemoveUnusedInputs() [d:\work\perforce\streams\devmobile\engine\source\developer\shadercompilercommon\private\hlslutils.cpp:1361]
ShaderCompileWorker-ShaderFormatD3D.dll!CompileAndProcessD3DShader() [d:\work\perforce\streams\devmobile\engine\source\developer\windows\shaderformatd3d\private\d3d11shadercompiler.cpp:570]
ShaderCompileWorker-ShaderFormatD3D.dll!CompileD3D11Shader() [d:\work\perforce\streams\devmobile\engine\source\developer\windows\shaderformatd3d\private\d3d11shadercompiler.cpp:991]
ShaderCompileWorker-ShaderFormatD3D.dll!CompileShader_Windows_SM5() [d:\work\perforce\streams\devmobile\engine\source\developer\windows\shaderformatd3d\private\d3d11shadercompiler.cpp:1038]
ShaderCompileWorker.exe!ProcessCompilationJob() [d:\work\perforce\streams\devmobile\engine\source\programs\shadercompileworker\private\shadercompileworker.cpp:122]
ShaderCompileWorker.exe!FWorkLoop::ProcessShaderPipelineCompilationJob() [d:\work\perforce\streams\devmobile\engine\source\programs\shadercompileworker\private\shadercompileworker.cpp:354]
ShaderCompileWorker.exe!FWorkLoop::ProcessInputFromArchive() [d:\work\perforce\streams\devmobile\engine\source\programs\shadercompileworker\private\shadercompileworker.cpp:338]
ShaderCompileWorker.exe!FWorkLoop::Loop() [d:\work\perforce\streams\devmobile\engine\source\programs\shadercompileworker\private\shadercompileworker.cpp:160]
ShaderCompileWorker.exe!GuardedMain() [d:\work\perforce\streams\devmobile\engine\source\programs\shadercompileworker\private\shadercompileworker.cpp:795]
ShaderCompileWorker.exe!GuardedMainWrapper() [d:\work\perforce\streams\devmobile\engine\source\programs\shadercompileworker\private\shadercompileworker.cpp:822]
ShaderCompileWorker.exe!wmain() [d:\work\perforce\streams\devmobile\engine\source\programs\shadercompileworker\private\shadercompileworker.cpp:937]
ShaderCompileWorker.exe!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:253]