Unfortunately, I haven't found an answer to this question, but I have developed an alternative.

I wrote a program in C++ that reads the shader code as std::string and searches it for “#include”. When it occurs, I recursively loaded this file and replaced the content accordingly. Since this happens recursively, “#include” can also be in included files. The finished string is written to a temporary file at the end and compiled to Spir-V using a batch file.

static std::vector<std::string> split(const std::string& text, const std::string& delimiter){    std::vector<std::string> result;    std::string s = text;    std::string d = delimiter;    size_t pos = 0;    std::string token;    while ((pos = s.find(d)) != std::string::npos) {        token = s.substr(0, pos);        result.push_back(token);        s.erase(0, pos + d.length());    }    result.push_back(s);    return result;}static std::string getIncludeFileName(std::string includeCode){    std::string result = "";    bool recording = false;    for (unsigned int i = 0; i < includeCode.length(); ++i) {        if (includeCode.at(i) == 34) // find '"'            recording = !recording;        else            if (recording)                result += includeCode.at(i);    }    return result;}static std::string loadShaderCode(const std::string& shaderCodeFile) //can handle "#include" within the shader code{    std::string result = "";    std::ifstream file(shaderCodeFile);    std::string directory = "";    std::vector<std::string> splittedPath = split(shaderCodeFile, "/");    for (unsigned int i = 0; i < splittedPath.size() - 1; ++i)        directory += splittedPath[i] + "/";    std::string line;    while (std::getline(file, line)) {        if (line.length() > 8 && line.substr(0, 8).compare("#include") == 0) {            //#include found            std::string includeFile = getIncludeFileName(line);            result += loadShaderCode(directory + "/" + includeFile);        }        else            result += line + "\n";    }    return result;}

• glsl
• vulkan