remove unneeded preexec function option from cpp-subprocess

We don't seem to ever need this, so remove it.

Author: theStack

src/util/subprocess.hpp

@@ -845,44 +845,6 @@ struct error
   int wr_ch_ = -1;
 };
 
-// Impoverished, meager, needy, truly needy
-// version of type erasure to store function pointers
-// needed to provide the functionality of preexec_func
-// ATTN: Can be used only to execute functions with no
-// arguments and returning void.
-// Could have used more efficient methods, ofcourse, but
-// that won't yield me the consistent syntax which I am
-// aiming for. If you know, then please do let me know.
-
-class preexec_func
-{
-public:
-  preexec_func() {}
-
-  template <typename Func>
-  explicit preexec_func(Func f): holder_(new FuncHolder<Func>(std::move(f)))
-  {}
-
-  void operator()() {
-    (*holder_)();
-  }
-
-private:
-  struct HolderBase {
-    virtual void operator()() const = 0;
-    virtual ~HolderBase(){};
-  };
-  template <typename T>
-  struct FuncHolder: HolderBase {
-    FuncHolder(T func): func_(std::move(func)) {}
-    void operator()() const override { func_(); }
-    // The function pointer/reference
-    T func_;
-  };
-
-  std::unique_ptr<HolderBase> holder_ = nullptr;
-};
-
 // ~~~~ End Popen Args ~~~~
 
 
@@ -990,7 +952,6 @@ struct ArgumentDeducer
   void set_option(output&& out);
   void set_option(error&& err);
   void set_option(close_fds&& cfds);
-  void set_option(preexec_func&& prefunc);
   void set_option(session_leader&& sleader);
 
 private:
@@ -1323,13 +1284,11 @@ class Popen
 
   bool defer_process_start_ = false;
   bool close_fds_ = false;
-  bool has_preexec_fn_ = false;
   bool session_leader_ = false;
 
   std::string exe_name_;
   std::string cwd_;
   env_map_t env_;
-  preexec_func preexec_fn_;
 
   // Command in string format
   std::string args_;
@@ -1669,11 +1628,6 @@ namespace detail {
     popen_->close_fds_ = cfds.close_all;
   }
 
-  inline void ArgumentDeducer::set_option(preexec_func&& prefunc) {
-    popen_->preexec_fn_ = std::move(prefunc);
-    popen_->has_preexec_fn_ = true;
-  }
-
 
   inline void Child::execute_child() {
 #ifndef __USING_WINDOWS__
@@ -1737,10 +1691,6 @@ namespace detail {
         if (sys_ret == -1) throw OSError("chdir failed", errno);
       }
 
-      if (parent_->has_preexec_fn_) {
-        parent_->preexec_fn_();
-      }
-
       if (parent_->session_leader_) {
         sys_ret = setsid();
         if (sys_ret == -1) throw OSError("setsid failed", errno);