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, 5 insertions, 1 deletions

diff --git a/unwind.h b/unwind.h
index 1a122ebd..30ab70c2 100644
--- a/unwind.h
+++ b/unwind.h
@@ -30,7 +30,7 @@ typedef enum uw_frtype {
   UW_BLOCK, UW_CAPTURED_BLOCK, UW_MENV, UW_CATCH, UW_HANDLE,
   UW_CONT_COPY, UW_GUARD,
 #if CONFIG_DEBUG_SUPPORT
-  UW_FCALL, UW_EVAL
+  UW_FCALL, UW_EVAL, UW_EXPAND
 #endif
 } uw_frtype_t;
 
@@ -146,6 +146,7 @@ void uw_push_handler(uw_frame_t *, val matches, val fun);
 #if CONFIG_DEBUG_SUPPORT
 void uw_push_fcall(uw_frame_t *, val fun, struct args *args);
 void uw_push_eval(uw_frame_t *, val form, val env);
+void uw_push_expand(uw_frame_t *, val form, val env);
 #endif
 noreturn val uw_throw(val sym, val exception);
 noreturn val uw_throwv(val sym, struct args *);
@@ -174,6 +175,9 @@ val uw_find_frame(val extype, val frtype);
 val uw_find_frames(val extype, val frtype);
 #if CONFIG_DEBUG_SUPPORT
 val uw_find_frames_by_mask(val mask);
+val uw_last_form_expanded(void);
+#else
+define uw_last_form_expanded() ((void) 0)
 #endif
 val uw_invoke_catch(val catch_frame, val sym, struct args *);
 val uw_muffle_warning(val exc, struct args *);