fix compare schematics if no file for schematic to compare with is given. In this case compare current schematic with saved version. Also issue a warning if swapping compare schematics if comparing schematic with disk version of itself.

src/callback.c

@@ -1108,7 +1108,7 @@ int callback(const char *winpath, int event, int mx, int my, KeySym key,
       /* redraw selection on expose, needed if no backing store available on the server 20171112 */
       XSetClipRectangles(display, xctx->gc[SELLAYER], 0,0, xr, 1, Unsorted);
       rebuild_selected_array();
-      if(tclgetboolvar("compare_sch") && xctx->sch_to_compare[0]){
+      if(tclgetboolvar("compare_sch") /* && xctx->sch_to_compare[0] */){
         compare_schematics("");
       } else {
         draw_selection(xctx->gc[SELLAYER],0);

src/draw.c

@@ -3825,7 +3825,7 @@ void draw(void)
                       xctx->xrect[0].width, xctx->xrect[0].height);
       #endif
     }
-    if(tclgetboolvar("compare_sch") && xctx->sch_to_compare[0]){
+    if(tclgetboolvar("compare_sch") /* && xctx->sch_to_compare[0]*/ ){
       compare_schematics("");
     } else {
       draw_selection(xctx->gc[SELLAYER], 0); /* 20181009 moved outside of cadlayers loop */

src/xinit.c

@@ -685,6 +685,7 @@ int compare_schematics(const char *f)
   int_hash_init(&table1, HASHSIZE);
   int_hash_init(&table2, HASHSIZE);
 
+  dbg(1, "compare_schematics(): xctx->sch_to_compare=%s\n", xctx->sch_to_compare);
   /* set filename of schematic to compare */
   if(f == NULL) {
     tcleval("load_file_dialog {Schematic to compare with} *.\\{sch,sym\\} INITIALLOADDIR");

src/xschem.tcl

@@ -4773,6 +4773,12 @@ proc swap_compare_schematics {} {
   global compare_sch XSCHEM_TMP_DIR
   set sch1 [xschem get schname]
   set sch2 [xschem get sch_to_compare]
+  if { $sch1 eq $sch2} {
+    set msg "Swapping with same schematic name on disk. Suggest to cancel to avoid losing/overwriting data"
+    set answer [tk_messageBox -message  $msg \
+       -icon warning -parent [xschem get topwindow]  -type okcancel]
+    if { $answer ne {ok} } {return} 
+  }
   puts "swap_compare_schematics:\n  sch1=$sch1\n  sch2=$sch2"
   if {$sch2 ne {}} {
     xschem load $sch2 nofullzoom gui