feature/zach-soc-bytecode-in-traceback 11b403c 1/3: Print byte offset of error in backtrace

[Rocky Bernstein]

branch: feature/zach-soc-bytecode-in-traceback
commit 11b403cb230f7f447fa7b988412b9f07b89ac3b6
Author: Zach Shaftel <zshaftel@gmail.com>
Commit: Zach Shaftel <zshaftel@gmail.com>

    Print byte offset of error in backtrace
---
 lisp/emacs-lisp/debug.el |  6 ++++--
 src/bytecode.c           |  5 +++--
 src/eval.c               | 14 +++++++++++++-
 src/lisp.h               |  1 +
 4 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index ed28997..db2943b 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -335,8 +335,10 @@ That buffer should be current already and in 
debugger-mode."
           nil))
 
   (setq backtrace-view (plist-put backtrace-view :show-flags t)
-        backtrace-insert-header-function (lambda ()
-                                           (debugger--insert-header args))
+        backtrace-insert-header-function
+        (lambda ()
+          (insert (format "Byte-code offset of error: %d\n" (car (last args))))
+          (debugger--insert-header args))
         backtrace-print-function debugger-print-function)
   (backtrace-print)
   ;; Place point on "stack frame 0" (bug#15101).
diff --git a/src/bytecode.c b/src/bytecode.c
index 8ef8468..1c98a51 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -424,13 +424,14 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, 
Lisp_Object maxdepth,
         Threading provides a performance boost.  These macros are how
         we allow the code to be compiled both ways.  */
 #ifdef BYTE_CODE_THREADED
+#define UPDATE_OFFSET (backtrace_byte_offset = pc - bytestr_data);
       /* The CASE macro introduces an instruction's body.  It is
         either a label or a case label.  */
 #define CASE(OP) insn_ ## OP
       /* NEXT is invoked at the end of an instruction to go to the
         next instruction.  It is either a computed goto, or a
         plain break.  */
-#define NEXT goto *(targets[op = FETCH])
+#define NEXT UPDATE_OFFSET goto *(targets[op = FETCH])
       /* FIRST is like NEXT, but is only used at the start of the
         interpreter body.  In the switch-based interpreter it is the
         switch, so the threaded definition must include a semicolon.  */
@@ -1448,7 +1449,7 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, 
Lisp_Object maxdepth,
        unbind_to (count, Qnil);
       error ("binding stack not balanced (serious byte compiler bug)");
     }
-
+  backtrace_byte_offset = -1;
   Lisp_Object result = TOP;
   SAFE_FREE ();
   return result;
diff --git a/src/eval.c b/src/eval.c
index 4251c3e..82463c4 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -56,6 +56,8 @@ Lisp_Object Vrun_hooks;
 /* FIXME: We should probably get rid of this!  */
 Lisp_Object Vsignaling_function;
 
+int backtrace_byte_offset = -1;
+
 /* These would ordinarily be static, but they need to be visible to GDB.  */
 bool backtrace_p (union specbinding *) EXTERNALLY_VISIBLE;
 Lisp_Object *backtrace_args (union specbinding *) EXTERNALLY_VISIBLE;
@@ -335,7 +337,10 @@ call_debugger (Lisp_Object arg)
         redisplay, which necessarily leads to display problems.  */
   specbind (Qinhibit_eval_during_redisplay, Qt);
 #endif
-
+  if (backtrace_byte_offset >= 0) {
+    arg = CALLN(Fappend, arg, list1(make_fixnum(backtrace_byte_offset)));
+    backtrace_byte_offset = -1;
+  }
   val = apply1 (Vdebugger, arg);
 
   /* Interrupting redisplay and resuming it later is not safe under
@@ -1696,6 +1701,13 @@ signal_or_quit (Lisp_Object error_symbol, Lisp_Object 
data, bool keyboard_quit)
 /* Like xsignal, but takes 0, 1, 2, or 3 args instead of a list.  */
 
 void
+xsignal_with_offset (Lisp_Object error_symbol, Lisp_Object data, int 
bytecode_offset)
+{
+  backtrace_byte_offset = bytecode_offset;
+  xsignal(error_symbol, data);
+}
+
+void
 xsignal0 (Lisp_Object error_symbol)
 {
   xsignal (error_symbol, Qnil);
diff --git a/src/lisp.h b/src/lisp.h
index c9b069b..ff60dfa 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4089,6 +4089,7 @@ extern Lisp_Object Vautoload_queue;
 extern Lisp_Object Vrun_hooks;
 extern Lisp_Object Vsignaling_function;
 extern Lisp_Object inhibit_lisp_code;
+extern int backtrace_byte_offset;
 
 /* To run a normal hook, use the appropriate function from the list below.
    The calling convention: