avoid quitting the program for some serious but non fatal errors, add some error reporting, some documentation updates (faq.html)

doc/xschem_man/faq.html

@@ -49,6 +49,14 @@ p{padding: 15px  30px 10px;}
  </p>
   
 
+ <h3> I start xschem in the background and it freezes. Why?</h3>
+ <p class="faq">
+ XSCHEM is usually launched from a terminal, the terminal becomes a TCL shell where commands can be sent to xschem.
+ For this reason XSCHEM should not be launched in background, as any I/O operation to/from the terminal will block
+ the program. If you don't plan to use the terminal just start XSCHEM with the -b option: <kbd>xschem -b</kbd>. 
+ XSCHEM will fork itself in the background detaching from the terminal.
+ </p>
+
  <h3> </h3>
  <p class="faq">
 

src/callback.c

@@ -743,7 +743,7 @@ int callback(const char *winpath, int event, int mx, int my, KeySym key,
                    "[get_cell [xschem get schname] 0]"
                    ": UNSAVED data: want to exit?\"");
          }
-         if(!xctx->modified || !strcmp(tclresult(),"ok")) tcleval( "exit");
+         if(!xctx->modified || !strcmp(tclresult(),"ok")) tcleval("exit");
        }
      } else {
        /* xschem new_schematic destroy asks user confirmation if schematic changed */

src/psprint.c

@@ -673,7 +673,8 @@ void create_ps(char **psfile, int what)
   }
   ps_colors=my_calloc(311, cadlayers, sizeof(Ps_color));
   if(ps_colors==NULL){
-    fprintf(errfp, "create_ps(): calloc error\n");tcleval( "exit");
+    fprintf(errfp, "create_ps(): calloc error\n");
+    return;
   }
 
   fill_ps_colors();

src/save.c

@@ -1169,8 +1169,9 @@ static void init_undo(void)
   if(!xctx->undo_initialized) {
     /* create undo directory */
     if( !my_strdup(644, &xctx->undo_dirname, create_tmpdir("xschem_undo_") )) {
-      fprintf(errfp, "xinit(): problems creating tmp undo dir\n");
-      tcleval("exit");
+      dbg(0, "xinit(): problems creating tmp undo dir, Undo will be disabled\n");
+      dbg(0, "xinit(): Check permissions in %s\n", XSCHEM_TMP_DIR);
+      xctx->no_undo = 1; /* disable undo */
     }
     xctx->undo_initialized = 1;
   }
@@ -1424,8 +1425,9 @@ static void get_sym_type(const char *symname, char **type,
           case 'B':
            fscan_ret = fscanf(fd, "%d",&c);
            if(fscan_ret != 1 || c <0 || c>=cadlayers) {
-             fprintf(errfp,"FATAL: box layer wrong or missing or > defined cadlayers, increase cadlayers\n");
-             tcleval( "exit");
+             fprintf(errfp,"get_sym_type(): box layer wrong or missing or > defined cadlayers, ignoring, increase cadlayers\n");
+             ungetc(tag[0], fd);
+             read_record(tag[0], fd, 1);
            }
            fscan_ret = fscanf(fd, "%lf %lf %lf %lf ",&box.x1, &box.y1, &box.x2, &box.y2);
            if(fscan_ret < 4) dbg(0, "Warning: missing fields in 'B' line\n");
@@ -1698,7 +1700,7 @@ int load_sym_def(const char *name, FILE *embed_fd)
       if((lcc[level].fd=fopen(sympath, fopen_read_mode))==NULL)
       {
        fprintf(errfp, "l_s_d(): systemlib/missing.sym missing, I give up\n");
-       tcleval( "exit");
+       tcleval("exit");
       }
     }
     dbg(1, "l_s_d(): fopen1(%s), level=%d, fd=%p\n",sympath, level, lcc[level].fd);

src/svgdraw.c

@@ -577,7 +577,8 @@ void svg_draw(void)
   svg_restore_lw();
   svg_colors=my_calloc(419, cadlayers, sizeof(Svg_color));
   if(svg_colors==NULL){
-    fprintf(errfp, "svg_draw(): calloc error\n");tcleval( "exit");
+    fprintf(errfp, "svg_draw(): calloc error\n");
+    return;
   }
   fill_svg_colors();
   old_grid=tclgetboolvar("draw_grid");

src/xschem.tcl

@@ -105,7 +105,7 @@ proc execute_wait {status args} {
 # while waiting for process to end.
 proc execute {status args} {
   global execute_id execute_status
-  global execute_data
+  global execute_data has_x
   global execute_cmd
   global execute_pipe
   if {![info exists execute_id]} {
@@ -116,6 +116,10 @@ proc execute {status args} {
   set id $execute_id
   if { [catch {open "|$args" r} err] } {
     puts stderr "Proc execute error: $err"
+    if { [info exists has_x]} {
+        tk_messageBox -message  "Can not execute '$args': ensure it is available on the system. Error: $err" \
+            -icon error -parent [xschem get topwindow] -type ok
+    }
     return -1
   } else {
     set pipe $err