* lisp/emacs-lisp/debug.el (debugger-toggle-locals): New command.

(debugger-mode-map): Bind it.
(debugger--backtrace-base): New function.
(debugger-eval-expression): Use it.
(debugger-frame-number): Skip local vars when present.
(debugger--locals-visible-p, debugger--insert-locals)
(debugger--show-locals, debugger--hide-locals): New functions.
* src/eval.c (Fbacktrace__locals): New function.
(syms_of_eval): Defsubr it.

1 files changed, 68 insertions, 0 deletions

diff --git a/src/eval.c b/src/eval.c
index d3fcec5aef4..81666830f4e 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3576,6 +3576,73 @@ NFRAMES and BASE specify the activation frame to use, as in `backtrace-frame'.
      from the debugger.  */
   return unbind_to (count, eval_sub (exp));
 }
+
+DEFUN ("backtrace--locals", Fbacktrace__locals, Sbacktrace__locals, 1, 2, NULL,
+       doc: /* Return names and values of local variables of a stack frame.
+NFRAMES and BASE specify the activation frame to use, as in `backtrace-frame'.  */)
+  (Lisp_Object nframes, Lisp_Object base)
+{
+  union specbinding *frame = get_backtrace_frame (nframes, base);
+  union specbinding *prevframe
+    = get_backtrace_frame (make_number (XFASTINT (nframes) - 1), base);
+  ptrdiff_t distance = specpdl_ptr - frame;
+  Lisp_Object result = Qnil;
+  eassert (distance >= 0);
+
+  if (!backtrace_p (prevframe))
+    error ("Activation frame not found!");
+  if (!backtrace_p (frame))
+    error ("Activation frame not found!");
+
+  /* The specpdl entries normally contain the symbol being bound along with its
+     `old_value', so it can be restored.  The new value to which it is bound is
+     available in one of two places: either in the current value of the
+     variable (if it hasn't been rebount yet) or in the `old_value' slot of the
+     next specpdl entry for it.
+     `backtrace_eval_unrewind' happens to swap the role of `old_value'
+     and "new value", so we abuse it here, to fetch the new value.
+     It's ugly (we'd rather not modify global data) and a bit inefficient,
+     but it does the job for now.  */
+  backtrace_eval_unrewind (distance);
+
+  /* Grab values.  */
+  {
+    union specbinding *tmp = prevframe;
+    for (; tmp > frame; tmp--)
+      {
+        switch (tmp->kind)
+          {
+          case SPECPDL_LET:
+          case SPECPDL_LET_DEFAULT:
+          case SPECPDL_LET_LOCAL:
+            {
+              Lisp_Object sym = specpdl_symbol (tmp);
+              Lisp_Object val = specpdl_old_value (tmp);
+              if (EQ (sym, Qinternal_interpreter_environment))
+                {
+                  Lisp_Object env = val;
+                  for (; CONSP (env); env = XCDR (env))
+                    {
+                      Lisp_Object binding = XCAR (env);
+                      if (CONSP (binding))
+                        result = Fcons (Fcons (XCAR (binding),
+                                               XCDR (binding)),
+                                        result);
+                    }
+                }
+              else
+                result = Fcons (Fcons (sym, val), result);
+            }
+          }
+      }
+  }
+
+  /* Restore values from specpdl to original place.  */
+  backtrace_eval_unrewind (-distance);
+
+  return result;
+}
+
 
 void
 mark_specpdl (void)
@@ -3824,6 +3891,7 @@ alist of active lexical bindings.  */);
   defsubr (&Sbacktrace);
   defsubr (&Sbacktrace_frame);
   defsubr (&Sbacktrace_eval);
+  defsubr (&Sbacktrace__locals);
   defsubr (&Sspecial_variable_p);
   defsubr (&Sfunctionp);
 }