WIP: add workaround for older Boost versions without process v2

Not sure whether Boost 1.811.0 is the correct version to make the
cut, because the changelog of Boost Process is ... sparse.

Author: striezel

code/html_generation.cpp

@@ -21,9 +21,14 @@
 #include "html_generation.hpp"
 #include <fstream>
 #include <iostream>
-#include <boost/asio/io_context.hpp>
-#include <boost/process/v2/process.hpp>
-#include <boost/process/v2/posix/fork_and_forget_launcher.hpp>
+#include <boost/version.hpp>
+#if BOOST_VERSION <= 108100
+  #include <boost/process.hpp>
+#else
+  #include <boost/asio/io_context.hpp>
+  #include <boost/process/v2/process.hpp>
+  #include <boost/process/v2/posix/fork_and_forget_launcher.hpp>
+#endif
 #include "browser_detection.hpp"
 #include "Config.hpp"
 #include "paths.hpp"
@@ -69,12 +74,24 @@ void openFirstIndexFile(const FolderMap& fm, const std::string& html_dir)
   }
   // Open file via Boost Process.
   std::cout << "Opening " << fullFileName << " in browser ...\n";
-  boost::asio::io_context context;
   std::vector<std::string> params = additional_parameters(browser.value().type);
+  #if BOOST_VERSION <= 108100
+  std::string command = browser.value().path.string();
+  for (const auto& param: params)
+  {
+    command += " " + param;
+  }
+  command += " " + fullFileName;
+  boost::process::child child(command);
+  child.detach();
+  #else
+  // After Boost 1.81.0 use process v2 API.
+  boost::asio::io_context context;
   params.push_back(fullFileName);
   auto launcher = boost::process::v2::posix::fork_and_forget_launcher();
   boost::process::v2::process proc(context, browser.value().path.string(), params);
   proc.detach();
+  #endif
 }
 
 int generateHtmlFiles(const MessageDatabase& mdb, const FolderMap& fm, const HTMLOptions htmlOptions)