commit 873d355ec271b22f0e48dac1c8eaca7deb075e66
Author:     Matthias Melcher <github@matthiasm.com>
AuthorDate: Fri Jan 27 11:35:05 2023 +0100
Commit:     Matthias Melcher <github@matthiasm.com>
CommitDate: Fri Jan 27 11:35:17 2023 +0100

    FLUID: fixe external command alert on Unix

 fluid/ExternalCodeEditor_UNIX.cxx | 34 +++++++++++++++++++++++++++++++++-
 fluid/ExternalCodeEditor_UNIX.h   |  6 ++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git fluid/ExternalCodeEditor_UNIX.cxx fluid/ExternalCodeEditor_UNIX.cxx
index 687927f..2860767 100644
--- fluid/ExternalCodeEditor_UNIX.cxx
+++ fluid/ExternalCodeEditor_UNIX.cxx
@@ -59,6 +59,11 @@ ExternalCodeEditor::ExternalCodeEditor() {
   filename_   = 0;
   file_mtime_ = 0;
   file_size_  = 0;
+  if (::pipe(alert_pipe_) == 0) {
+    Fl::add_fd(alert_pipe_[0], FL_READ, alert_pipe_cb, this);
+  } else {
+    alert_pipe_[0] = alert_pipe_[1] = -1;
+  }
 }
 
 /**
@@ -71,6 +76,8 @@ ExternalCodeEditor::~ExternalCodeEditor() {
            (void*)this, (long)pid_);
   close_editor();   // close editor, delete tmp file
   set_filename(0);  // free()s filename
+  if (alert_pipe_[0] != -1) ::close(alert_pipe_[0]);
+  if (alert_pipe_[1] != -1) ::close(alert_pipe_[1]);
 }
 
 /**
@@ -360,6 +367,7 @@ int ExternalCodeEditor::start_editor(const char *editor_cmd,
                         editor_cmd, filename);
   char cmd[1024];
   snprintf(cmd, sizeof(cmd), "%s %s", editor_cmd, filename);
+  command_line_.value(editor_cmd);
   // Fork editor to background..
   switch ( pid_ = fork() ) {
     case -1:    // error
@@ -367,11 +375,14 @@ int ExternalCodeEditor::start_editor(const char *editor_cmd,
       return -1;
     case 0: {   // child
       // NOTE: OSX wants minimal code between fork/exec, see Apple TN2083
+      // NOTE: no FLTK calls after a fork. Use a pipe to tell the app if the
+      //       command can't launch
       int nargs;
       char **args = 0;
       if (make_args(cmd, &nargs, &args) > 0) {
         execvp(args[0], args);  // run command - doesn't return if succeeds
-        fl_alert("couldn't exec() '%s': %s", cmd, strerror(errno));
+        int err = errno;
+        ::write(alert_pipe_[1], &err, sizeof(int));
         exit(1);
       }
       exit(1);
@@ -516,3 +527,24 @@ void ExternalCodeEditor::set_update_timer_callback(Fl_Timeout_Handler cb) {
 int ExternalCodeEditor::editors_open() {
   return L_editors_open;
 }
+
+/**
+ It the forked process can't run the editor, it will send the errno through a pipe.
+ */
+void ExternalCodeEditor::alert_pipe_cb(FL_SOCKET s, void* d) {
+  ExternalCodeEditor* self = (ExternalCodeEditor*)d;
+  self->last_error_ = 0;
+  ::read(s, &self->last_error_, sizeof(int));
+  const char* cmd = self->command_line_.value();
+  if (cmd && *cmd) {
+    if (cmd[0] == '/') { // is this an absoluet filename?
+      fl_alert("Can't launch external editor '%s':\n%s\n\ncmd: \"%s\")",
+               fl_filename_name(cmd), strerror(self->last_error_), cmd);
+    } else {
+      char pwd[FL_PATH_MAX+1];
+      fl_getcwd(pwd, FL_PATH_MAX);
+      fl_alert("Can't launch external editor '%s':\n%s\n\ncmd: \"%s\"\npwd: \"%s\"",
+               fl_filename_name(cmd), strerror(self->last_error_), cmd, pwd);
+    }
+  }
+}
diff --git fluid/ExternalCodeEditor_UNIX.h fluid/ExternalCodeEditor_UNIX.h
index 186a5b5..87feba8 100644
--- fluid/ExternalCodeEditor_UNIX.h
+++ fluid/ExternalCodeEditor_UNIX.h
@@ -9,6 +9,8 @@
 
 #include <FL/Fl.H>
 
+#include "fluid.h"
+
 #include <errno.h>      /* errno */
 #include <string.h>     /* strerror() */
 #include <sys/types.h>  /* stat().. */
@@ -22,6 +24,10 @@ class ExternalCodeEditor {
   time_t file_mtime_;                   // last modify time of the file (used to determine if file changed)
   size_t file_size_;                    // last file size (used to determine if changed)
   const char *filename_;
+  Fd_String command_line_;
+  int last_error_;
+  int alert_pipe_[2];
+  static void alert_pipe_cb(FL_SOCKET, void*);
 
 protected:
   void kill_editor();