remove a old backup before creating a new one

src/driver/whyconf.ml

@@ -28,7 +28,7 @@ open Rc
   - 5 cvc3 native
   - 6 driver renaming
   - 7 yices native (used for release 0.70)
-  - 8 for release 0.71 
+  - 8 for release 0.71
 
 If a configuration doesn't contain the actual magic number we don't use it.*)
 
@@ -247,7 +247,7 @@ let read_config conf_file =
 
 let save_config config =
   let filename = config.conf_file in
-  if Sys.file_exists filename then Sys.rename filename (filename ^ ".bak");
+  Sysutil.backup_file filename;
   to_file filename config.config
 
 let get_main config = config.main

src/ide/session.ml

@@ -610,6 +610,8 @@ let schedule_edit_proof ~debug:_ ~editor ~file ~driver ~callback goal =
     then
       begin
         let backup = file ^ ".bak" in
+        if Sys.file_exists backup
+          then Sys.remove backup;
         Sys.rename file backup;
         Some(open_in backup)
       end
@@ -1537,11 +1539,7 @@ let save_session () =
   match !current_env with
     | Some _ ->
         let f = Filename.concat !project_dir db_filename in
-        begin if Sys.file_exists f then
-          let b = f ^ ".bak" in
-          if Sys.file_exists b then Sys.remove b ;
-          Sys.rename f b
-        end;
+        Sysutil.backup_file f;
         save f
     | None ->
         eprintf "Session.save_session: no session opened@.";

src/util/sysutil.ml

@@ -17,6 +17,13 @@
 (*                                                                        *)
 (**************************************************************************)
 
+let backup_file f =
+  if Sys.file_exists f then begin
+    let fb = f ^ ".bak" in
+    if Sys.file_exists fb then Sys.remove fb;
+    Sys.rename f fb
+  end
+
 let channel_contents_fmt cin fmt =
   let buff = String.make 1024 ' ' in
   let n = ref 0 in

src/util/sysutil.mli

@@ -17,6 +17,9 @@
 (*                                                                        *)
 (**************************************************************************)
 
+(* create a backup copy of a file if it exists *)
+val backup_file : string -> unit
+
 (* return the content of an in-channel *)
 val channel_contents : in_channel -> string