[kernel] Avoid printing :0: in case of unknown loc

src/kernel_services/plugin_entry_points/log.ml

@@ -241,12 +241,15 @@ let rec echo_lines ?(prefix=false) output text p q =
 let add_source buffer = function
   | None -> ()
   | Some src ->
-    begin
+    (* Avoid printing ':0:' if the position is unknown. *)
+    if Filepath.is_empty_pos src
+    then Buffer.add_string buffer "<unknown location> "
+    else begin
       Buffer.add_string buffer
         (Filepath.Normalized.to_pretty_string src.Filepath.pos_path);
       Buffer.add_string buffer ":" ;
       Buffer.add_string buffer (string_of_int src.Filepath.pos_lnum);
-      Buffer.add_string buffer ": " ;
+      Buffer.add_string buffer ": "
     end
 
 let add_category buffer = function

src/plugins/aorai/tests/ya/oracle/floats.res.oracle

@@ -17,7 +17,7 @@
 [eva] floats.i:6: Warning: 
   no \from part
   for clause 'assigns aorai_CurOpStatus, aorai_CurOperation, aorai_CurStates;'
-[eva:alarm] :0: Warning: 
+[eva:alarm] <unknown location> Warning: 
   function square_root_aux, behavior Buchi_property_behavior: postcondition got status unknown.
 [eva:alarm] floats.i:11: Warning: 
   non-finite float value.

src/plugins/aorai/tests/ya/oracle_prove/floats.res.oracle

@@ -17,7 +17,7 @@
 [eva] floats.i:6: Warning: 
   no \from part
   for clause 'assigns aorai_CurOpStatus, aorai_CurOperation, aorai_CurStates;'
-[eva:alarm] :0: Warning: 
+[eva:alarm] <unknown location> Warning: 
   function square_root_aux, behavior Buchi_property_behavior: postcondition got status unknown.
 [eva:alarm] floats.i:11: Warning: 
   non-finite float value.

src/plugins/e-acsl/tests/bts/oracle/issue-framac-1119.res.oracle

 [e-acsl] beginning translation.
 [e-acsl] translation done in project "e-acsl".
-[eva:alarm] :0: Warning: 
+[eva:alarm] <unknown location> Warning: 
   function __e_acsl_assert_register_long: precondition data->values == \null ||
                                                        \valid(data->values) got status unknown.
 [eva:alarm] issue-framac-1119.c:10: Warning: