Use stricter input validation when looking for a string as input (bug #42651). * data.cc (get_sort_mode_option, Fissorted): Use is_string() to check string input. * debug.cc (Fdbstep): use "string" rather than "character string" in error messages. * error.cc (Flasterr, Flastwarn): use "string" rather than "character string" in error messages. * file-io.cc (do_stream_open, do_fread, do_fwrite, Fpopen, Ftempname, Fmkstemp): Use is_string() to check string input. * graphics.cc (Fgraphics_toolkit): Use is_string() to check string input. Rephrase error message. * help.cc (F__list_functions): Use is_string() to check string input. * input.cc (Fyes_or_no): Use is_string() to check string input. Rephrase error message. * input.cc (Fadd_input_event_hook): Rephrase error message. * load-path.cc (Fgenpath, Faddpath): Rephrase error message. * matrix_type.cc (Fmatrix_type): Use is_string() to check string input. * qz.cc (Fqz): Follow Octave coding convention for space after '!'. * regexp.cc (parse_options): Use is_string() to check string input. Rephrase error message. * schur.cc (Fschur): Use is_string() to check string input. * strfns.cc (Flist_in_columns): Use is_string() to check string input. Rephrase error message. * symtab.cc (Fignore_function_time_stamp): Use is_string() to check string input. Rephrase error message. * syscalls.cc (Fexec, Fpopen2, Fcanonicalize_file_name): Use is_string() to check string input. Rephrase error message. * sysdep.cc (Fsetenv): Use is_string() to check string input. * time.cc (Fstrftime, Fstrptime): Use is_string() to check string input. * toplev.cc (Fsystem, Fatexit): Use is_string() to check string input. * urlwrite.cc (Furlwrite, Furlread): Rephrase error message. * utils.cc (Ffile_in_path): Use is_string() to check string input. Rephrase error message. * variables.cc (extract_function): Add FIXME about potentially using is_string. * variables.cc (do_isglobal, Fmunlock, Fmislocked): Use is_string() to check string input. * variables.cc (set_internal_variable): Rephrase error message. * ov-base.cc (make_idx_args): Rephrase error message. * ov-class.cc (octave_class::all_strings, Fclass): Rephrase error message. * ov-fcn-handle.cc (Fstr2func): Use is_string() to check string input * ov-java.cc (FjavaObject, FjavaMethod, F__java_get__, F__java_set__): Use is_string() to check string input. * ov.cc (Fdecode_subscripts): Use is_string() to check string input. Rephrase error message. * pt-idx.cc (tree_index_expression::get_struct_index): Rephrase error message. * io.tst: Change %!warning test to %!error test to match stricter checking. * system.tst: Change %!warning test for setenv to %!error test to match stricter checking.

--- a/libinterp/corefcn/help.cc	Mon Dec 15 22:16:25 2014 -0800
+++ b/libinterp/corefcn/help.cc	Tue Dec 16 09:21:29 2014 -0800
@@ -1366,27 +1366,24 @@
 
   if (args.length () == 0)
     retval = Cell (ffl.append (afl));
-  else
+  else if (args(0).is_string ())
     {
       std::string dir = args(0).string_value ();
 
+      string_vector fl = load_path::files (dir, true);
+
       if (! error_state)
         {
-          string_vector fl = load_path::files (dir, true);
+          // Return a sorted list with unique entries (in case of
+          // .m and .oct versions of the same function in a given
+          // directory, for example).
+          fl.sort (true);
 
-          if (! error_state)
-            {
-              // Return a sorted list with unique entries (in case of
-              // .m and .oct versions of the same function in a given
-              // directory, for example).
-              fl.sort (true);
-
-              retval = Cell (fl);
-            }
+          retval = Cell (fl);
         }
-      else
-        error ("__list_functions__: DIRECTORY argument must be a string");
     }
+  else
+    error ("__list_functions__: DIRECTORY argument must be a string");
 
   return retval;
 }