Stop logging repeated errors when retrying

Retrying on an error that is not permanent but may last for a long time,
for hundreds or even thousands of attempts (for example, connection
refused, one of the roots not mounted), it is unnecessary to spam the
log with the same error every time.

src/fspath.ml

@@ -293,7 +293,7 @@ let canonizeFspath p0 =
             (try System.chdir parent with
                Sys_error why2 -> raise (Util.Fatal (Printf.sprintf
                  "Cannot find canonical name of %s: unable to cd either to it \
-(%s)\nor to its parent %s\n(%s)" p why parent why2)));
+(%s)\nor to its parent %s (%s)" p why parent why2)));
             System.getcwd () end in
           System.chdir original;
           let bn = Filename.basename p in

src/uitext.ml

@@ -158,6 +158,10 @@ let alwaysDisplay message =
   print_string message;
   flush stdout
 
+let alwaysDisplayErr message =
+  prerr_string message;
+  flush stderr
+
 let alwaysDisplayAndLog message =
 (*  alwaysDisplay message;*)
   Trace.log (message ^ "\n")
@@ -1580,19 +1584,39 @@ let getProfile default =
   askProfile ();
   !selection
 
-let handleException e =
+let suppressRepeatingMsg =
+  let prevMsg = ref "" in
+  let silencing = ref false in
+  fun retrying msg ->
+    match retrying with
+    | false ->
+        prevMsg := ""; silencing := false;
+        Some msg
+    | true when !prevMsg <> msg ->
+        prevMsg := msg; silencing := false;
+        Some msg
+    | true when not !silencing ->
+        silencing := true;
+        Some "\nRetrying continuously. The error above is repeating and \
+          is not logged repeatedly.\n"
+    | true ->
+        None
+
+let handleException ?(retrying = false) e =
   (* Keep the current status line (if any) and don't repeat it any more *)
   alwaysDisplay "\n";
   Util.set_infos "";
   restoreTerminal();
   let lbl =
     if e = Sys.Break then ""
-    else "Error: " in
+    else if not retrying then "Fatal error: " else "Error: " in
   let msg = lbl ^ Uicommon.exn2string e in
-  let () =
-    try Trace.log (msg ^ "\n")
-    with Util.Fatal _ -> () in (* Can't allow fatal errors in fatal error handler *)
-  if not !Trace.sendLogMsgsToStderr then alwaysDisplay ("\n" ^ msg ^ "\n")
+  alwaysDisplayErr (msg ^ "\n");
+  match suppressRepeatingMsg retrying msg with
+  | None -> ()
+  | Some msg ->
+      try Trace.logonly (msg ^ "\n")
+      with Util.Fatal _ -> () (* Can't allow fatal errors in fatal error handler *)
 
 let rec start interface =
   if interface <> Uicommon.Text then
@@ -1685,7 +1709,7 @@ and start2 () =
   | e -> begin
       (* If any other bad thing happened and the -repeat preference is
          set, then restart *)
-      handleException e;
+      handleException ~retrying:true e;
 
       Util.msg "\nRestarting in 10 seconds...\n\n";
       begin try interruptibleSleep 10 with Sys.Break -> terminate () end;