use exceptions for better invalid index error reporting (bug #45957) * lo-array-gripes.h, lo-array-gripes.cc (index_exception): New base class for indexing errors. (invalid_index, out_of_range): New classes. (gripe_index_out_of_range): New overloaded function. (gripe_invalid_index): New overloaded functions. Delete version with no arguments. (gripe_invalid_assignment_size, gripe_assignment_dimension_mismatch): Delete. Change uses of gripe functions as needed. * Cell.cc (Cell::index, Cell::assign, Cell::delete_elements): Use exceptions to collect error info about and handle indexing errors. * data.cc (Fnth_element, do_accumarray_sum, F__accumarray_sum__, do_accumarray_minmax, do_accumarray_minmax_fun, F__accumdim_sum__): Likewise. * oct-map.cc (octave_map::index, octave_map::assign, octave_map::delete_elements): Likewise. * sparse.cc (Fsparse): Likewise. * sub2ind.cc (Fsub2ind, Find2sub): Likewise. New tests. * utils.cc (dims_to_numel): Likewise. * ov-base-diag.cc (octave_base_diag<DMT, MT>::do_index_op, octave_base_diag<DMT, MT>::subsasgn): Likewise. * ov-base-mat.cc (octave_base_matrix<MT>::subsref, octave_base_matrix<MT>::assign): Likewise. * ov-base-sparse.cc (octave_base_sparse<T>::do_index_op, octave_base_sparse<T>::assign, octave_base_sparse<MT>::delete_elements): Likewise. * ov-classdef.cc (cdef_object_array::subsref, cdef_object_array::subsasgn): Likewise. * ov-java.cc (make_java_index): Likewise. * ov-perm.cc (octave_perm_matrix::do_index_op): Likewise. * ov-range.cc (octave_range::do_index_op): Likewise. * ov-re-diag.cc (octave_diag_matrix::do_index_op): Likewise. * ov-str-mat.cc (octave_char_matrix_str::do_index_op_internal): Likewise. * pt-assign.cc (tree_simple_assignment::rvalue1): Likewise. * pt-idx.cc (tree_index_expression::rvalue, tree_index_expression::lvalue): Likewise. * Array-util.cc (sub2ind): Likewise. * toplev.cc (main_loop): Also catch unhandled index_exception exceptions. * ov-base.cc (octave_base_value::index_vector): Improve error message. * ov-re-sparse.cc (octave_sparse_matrix::index_vector): Likewise. * ov-complex.cc (complex_index): New class. (gripe_complex_index): New function. (octave_complex::index_vector): Use it. * pt-id.h, pt-id.cc (tree_identifier::is_variable, tree_black_hole::is_variable): Now const. * pt-idx.cc (final_index_error): New static function. (tree_index_expression::rvalue, tree_index_expression::lvalue): Use it. * index.tst: New tests.

--- a/libinterp/octave-value/ov-re-diag.cc	Fri Oct 02 12:25:39 2015 -0400
+++ b/libinterp/octave-value/ov-re-diag.cc	Fri Oct 02 15:07:37 2015 -0400
@@ -92,31 +92,42 @@
   // vectors.
   if (! resize_ok && idx.length () == 2 && matrix.is_multiple_of_identity (1))
     {
-      idx_vector idx0 = idx(0).index_vector ();
-      idx_vector idx1 = idx(1).index_vector ();
-
-      if (! error_state)
+      int k = 0;        // index we're accesing when index_vector throws
+      try
         {
-          bool left = idx0.is_permutation (matrix.rows ());
-          bool right = idx1.is_permutation (matrix.cols ());
+          idx_vector idx0 = idx(0).index_vector ();
+          k = 1;
+          idx_vector idx1 = idx(1).index_vector ();
 
-          if (left && right)
+          if (! error_state)
             {
-              if (idx0.is_colon ()) left = false;
-              if (idx1.is_colon ()) right = false;
+              bool left = idx0.is_permutation (matrix.rows ());
+              bool right = idx1.is_permutation (matrix.cols ());
+
               if (left && right)
-                retval = PermMatrix (idx0, false) * PermMatrix (idx1, true);
-              else if (left)
-                retval = PermMatrix (idx0, false);
-              else if (right)
-                retval = PermMatrix (idx1, true);
-              else
                 {
-                  retval = this;
-                  this->count++;
+                  if (idx0.is_colon ()) left = false;
+                  if (idx1.is_colon ()) right = false;
+                  if (left && right)
+                    retval = PermMatrix (idx0, false) * PermMatrix (idx1, true);
+                  else if (left)
+                    retval = PermMatrix (idx0, false);
+                  else if (right)
+                    retval = PermMatrix (idx1, true);
+                  else
+                    {
+                      retval = this;
+                      this->count++;
+                    }
                 }
             }
         }
+      catch (index_exception& e)
+        {
+          // Rethrow to allow more info to be reported later.
+          e.set_pos_if_unset (2, k+1);
+          throw;
+        }
     }
 
   // if error_state is set, we've already griped.