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-complex.h
+++ b/libinterp/octave-value/ov-complex.h
@@ -43,6 +43,9 @@
 
 class tree_walker;
 
+extern void OCTAVE_API
+gripe_complex_index (Complex idx);
+
 // Complex scalar values.
 
 class
@@ -81,8 +84,7 @@
   // Use this to give a more specific error message
   idx_vector index_vector (bool /* require_integers */ = false) const
   {
-    error ("attempted to use a complex scalar as an index\n"
-           "       (forgot to initialize i or j?)");
+    gripe_complex_index (scalar);
     return idx_vector ();
   }