use more direct method for non-local symbol access (bug #38236) * pt-id.h, pd-id.cc (tree_evaluator::get_current_scope): New function. * symtab.h, symtab.cc (symbol_table::symbol_reference): Delete class. (symbol_table::dummy_symbol_record): Delete static data member. * oct-lvalue.h, oct-lvalue.cc (octave_lvalue::sym): Use symbol_record, not symbol_reference. Change all uses. (octave_lvalue::black_hole): New data member. (octave_lvalue:is_black_hole): Use it. (octave_lvalue::mark_black_hole): New function. * pt-eval.cc (tree_identifier::sym): Use symbol_record, not symbol_reference. Change all uses. (tree_black_hole::lvalue): Explicitly mark retval as black_hole. (tree_evaluator::visit_tree_identifier): Adapt to tree_identifier::symbol returning symbol_record, not symbol_reference. * oct-parse.in.yy (push_script_symtab, begin_file): New non-terminals. (file): Use begin_file to start script and classdef files. Use separate symbol table scope when parsing scripts. * ov-usr-fcn.h, ov-usr-fcn.cc (octave_user_code::m_scope): Move here from octave_user_fcn. (octave_user_code::scope): Likewise. (octave_user_script::octave_user_script): New argument scope. (octave_user_script::call): Add symbol_table::scope::unbind_script_symbols to unwind_protect frame. Call scope::bind_script_symbols to access evaluation scope. (octave_user_function::octave_user_function): Pass scope argument to octave_user_code base class. * symtab.h, symtab.cc (symbol_record_rep::m_fwd_rep): New data member. Change member functions to forward to secondary rep if it is defined. (symbol_record::bind_fwd_rep, symbol_record_rep::bind_fwd_rep, symbol_record::unbind_fwd_rep, symbol_record_rep::unbind_fwd_rep): New functions. (scope::bind_script_symbols, scope::unbind_script_symbols): New functions. (scope::varval, scope::global_varval, scope::top_level_varval): Now const. (scope::update_nest): Set forwarding rep for nonlocal symbol. (scope::look_nonlocal): Likewise.

--- a/libinterp/corefcn/oct-lvalue.h	Wed Sep 13 16:42:14 2017 -0700
+++ b/libinterp/corefcn/oct-lvalue.h	Wed Sep 13 17:10:51 2017 -0400
@@ -38,13 +38,13 @@
 {
 public:
 
-  octave_lvalue (const octave::symbol_table::symbol_reference& s
-                   = octave::symbol_table::symbol_reference ())
-    : sym (s), type (), idx (), nel (1)
+  octave_lvalue (const octave::symbol_table::symbol_record& s
+                   = octave::symbol_table::symbol_record ())
+    : sym (s), black_hole (false), type (), idx (), nel (1)
   { }
 
   octave_lvalue (const octave_lvalue& vr)
-    : sym (vr.sym), type (vr.type), idx (vr.idx), nel (vr.nel)
+    : sym (vr.sym), black_hole (vr.black_hole), type (vr.type), idx (vr.idx), nel (vr.nel)
   { }
 
   octave_lvalue& operator = (const octave_lvalue& vr)
@@ -52,6 +52,7 @@
     if (this != &vr)
       {
         sym = vr.sym;
+        black_hole = vr.black_hole;
         type = vr.type;
         idx = vr.idx;
         nel = vr.nel;
@@ -62,21 +63,23 @@
 
   ~octave_lvalue (void) = default;
 
-  bool is_black_hole (void) const { return sym.is_black_hole (); }
+  bool is_black_hole (void) const { return black_hole; }
+
+  void mark_black_hole (void) { black_hole = true; }
 
   bool is_defined (void) const
   {
-    return ! is_black_hole () && sym->is_defined ();
+    return ! is_black_hole () && sym.is_defined ();
   }
 
   bool is_undefined (void) const
   {
-    return is_black_hole () || sym->is_undefined ();
+    return is_black_hole () || sym.is_undefined ();
   }
 
   bool isstruct (void) const { return value().isstruct (); }
 
-  void define (const octave_value& v) { sym->assign (v); }
+  void define (const octave_value& v) { sym.assign (v); }
 
   void assign (octave_value::assign_op, const octave_value&);
 
@@ -98,7 +101,9 @@
 
 private:
 
-  octave::symbol_table::symbol_reference sym;
+  octave::symbol_table::symbol_record sym;
+
+  bool black_hole;
 
   std::string type;