debugger: expand frames.

This patch adds special unwind frames for backtracing
expansions. With this, we can get rid of the global variable
last_form_expanded, since to get the last form expanded, we
just search for the most enclosing expand frame.

* eval.c (last_form_expanded): Global variable removed.
(error_trace): Use uw_last_form_expanded() instead of
last_form_expanded.
(expand_eval): No need to save and restore
last_form_expanded any more.
(expand_lisp_setq, expand_setqf, expand_lisp1, do_expand): Use
uw_last_form_expanded().
(expand, do_macroexpand_1): Push and pop expand frame.
This fixes a bug: do_macroexpand_1 was not recording
last_form_expanded. Evaluation of top-level forms uses
explicit macroexpansion, therefore top-level evaluation was
neglecting to set last_form_expanded.
This explains weird behavior I saw in the listener from
time to time, when errors would report against the expansion
of the wrong form.
(eval_init): Remove reference to last_form_expanded variable.

* eval.h (last_form_expanded): Declaration removed.

* share/txr/stdlib/debug.tl (expand-frame print-trace,
expand-frame loc): New methods.
(print-backtrace): Include uw-expand frames in the backtrace.

* unwind.c (expand_frame_type): New static variable.
(uw_find_frames_by_mask): Handle UW_EXPAND.
(uw_last_form_expanded, uw_push_expand): New functions.
(uw_late_init): Register expand-frame struct type.

* unwind.h (enum uw_frtype): New enum member, UW_EXPAND.
(uw_last_form_expanded, uw_push_expand): Declared.

1 files changed, 10 insertions, 1 deletions

diff --git a/share/txr/stdlib/debugger.tl b/share/txr/stdlib/debugger.tl
index 8eeb9ce2..26f30741 100644
--- a/share/txr/stdlib/debugger.tl
+++ b/share/txr/stdlib/debugger.tl
@@ -78,6 +78,15 @@
                  ^[,(cadr form)]
                  ^(,sym)))))))
 
+(defmeth expand-frame print-trace (fr pr-fr nx-fr prefix)
+  (let* ((form fr.form)
+         (loc (source-loc-str form)))
+    (put-string `@prefix X:@(if loc `(@loc):`)`)
+    (prinl form)))
+
+(defmeth expand-frame loc (fr)
+  (source-loc-str fr.form))
+
 (defun print-backtrace (: (*stdout* *stdout*) (prefix ""))
   (with-resources ((imode (set-indent-mode *stdout* indent-foff)
                           (set-indent-mode *stdout* imode))
@@ -86,7 +95,7 @@
                    (length (set-max-length *stdout* 10)
                            (set-max-length *stdout* length)))
     (window-map 1 nil (lambda (pr el nx) el.(print-trace pr nx prefix))
-                (find-frames-by-mask (logior uw-fcall uw-eval)))))
+                (find-frames-by-mask (logior uw-fcall uw-eval uw-expand)))))
 
 (defun debugger ()
   (with-disabled-debugging