make dbup/dbdown work again (bug #56020) Store call stack index in stack frame object to make iteration in call stack possible given only a stack frame. Store current debug frame in call stack and use that info to track stack location when at a debug prompt. New class for managing debug info and the debug repl. It should now be possible to enter the debugger recursively. * stack-frame.h, stack-frame.cc (stack_frame::m_index): New data member. (stack_frame::m_prev): Delete data member and all uses. Update constructors for base and derived classes and change all uses. (stack_frame::index): New function. (display_stopped_in_message): New function. * bp-table.cc: Eliminate use of Vdebugger. Don't set debug_mode directly. * error.cc (maybe_enter_debugger, warning_1): Use tree_evaluator::enter_debugger instead of input_system::keyboard to enter debugger. * call-stack.h, call-stack.cc (call_stack::goto_frame_relative): Delete. (call_stack::find_current_user_frame, call_stack::find_current_user_frame, call_stack::find_current_user_frame, call_stack::find_caller_frame): New functions. (call_stack::goto_caller_frame): Simplify by calling find_caller_frame and dbupdown. (class stack_trace_generator): Delete class and all uses. (call_stack::current_user_code): Rename from caller_user_code and eliminate nskip argument. (call_stack::current_user_code_line): Rename from caller_user_code_line. (call_stack::current_user_code_column): Rename from caller_user_code_column. (call_stack::goto_frame, call_stack::dbupdown): Use stack_frame::display_in_stopped_message. (call_stack::backtrace_frames, call_stack::backtrace): Make these functions work again. Eliminate nskip argument. * debug.cc (Fdbstop, Fdbclear, Fdbstep): Call tree_evaluator::reset_debug_state. (Fdbstop, Fdbclear, Fdbstep, Fdbcont, Fdbquit, Fisdebugmode): Move real work to evaluator, debugger, and call_stack classes. (Fdbwhere): Use stack_frame::display_stopped_in_message. * input.h, input.cc (Vdebugging): Delete variable and all uses. (input_system::keyboard, execute_in_debugger_handler, input_system::get_debutg_input): Delete. Move functionality to new debugger class. (Fkeyboard): Simplify. (do_keyboard): Delete. * pt-eval.h, pt-eval.cc (class debugger): New class for managing debugger. (tree_evaluator::m_debug_frame): Rename from m_current_frame. Use this variable to manage debugger location when making function calls during debugging (for example, to dbup, dbdown, etc.). (tree_evaluator::m_debugger_stack): New variable. (tree_evaluator::reset_debug_state): Set m_debug_mode if we have breakpoints, are stepping in the debugger, or executing in the debugger repl. (tree_evaluator::reset_debug_state): Don't set m_dbstep_flag here. (tree_evaluator::enter_debugger): New function. (tree_evaluator::do_breakpoint): Handle exiting from the debugger object here. Maybe rejoin existing debugger instance. (tree_evaluator::do_keyboard): Delete. (bool tree_evaluator::in_debug_repl, bool tree_evaluator::exit_debug_repl, bool tree_evaluator::exit_debug_repl, bool tree_evaluator::abort_debug_repl, bool tree_evaluator::abort_debug_repl): New functions.

--- a/libinterp/corefcn/stack-frame.cc	Mon Apr 08 09:22:39 2019 -0700
+++ b/libinterp/corefcn/stack-frame.cc	Mon Apr 08 00:36:33 2019 +0000
@@ -478,6 +478,22 @@
     accept (sc);
   }
 
+  void stack_frame::display_stopped_in_message (std::ostream& os) const
+  {
+    if (index () == 0)
+      os << "at top level" << std::endl;
+    else
+      {
+        os << "stopped in " << fcn_name ();
+
+        int l = line ();
+        if (l > 0)
+          os << " at line " << line ();
+
+        os << " [" << fcn_file_name () << "] " << std::endl;
+      }
+  }
+
   void stack_frame::display (bool follow) const
   {
     std::ostream& os = octave_stdout;
@@ -500,7 +516,7 @@
 
     os << "line: " << m_line << std::endl;
     os << "column: " << m_column << std::endl;
-    os << "prev: " << m_prev << std::endl;
+    os << "index: " << m_index << std::endl;
 
     os << std::endl;
 
@@ -543,9 +559,9 @@
   script_stack_frame::script_stack_frame (call_stack& cs,
                                           octave_user_script *script,
                                           unwind_protect *up_frame,
-                                          size_t prev,
+                                          size_t index,
                                           stack_frame *static_link)
-    : stack_frame (cs, prev, static_link, get_access_link (static_link)),
+    : stack_frame (cs, index, static_link, get_access_link (static_link)),
       m_script (script), m_unwind_protect_frame (up_frame),
       m_lexical_frame_offsets (get_num_symbols (script), 1),
       m_value_offsets (get_num_symbols (script), 0)