[perl #41726] [PATCH] make lua fail more gracefully with an exception handler

[Julian Fondren]

# New Ticket Created by  "Julian Fondren" 
# Please include the string:  [perl #41726]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=41726 >


Currently, evaluating this:

  function bad (n) return n * bad(n) end bad(2)

will cause lua to produce -- infinitely, and very
quickly -- ungraceful error messages.  (It will do
this on any excess-recursion error -- I first saw
this behavior when I passed too-large a number to
a simple factorial function.)

The attached patch causes lua to generate .pir
files that push this exception handler before
evaluating any compiled-lua code:

  root_exception_handler:
    get_results '(0, 0)', $P0, $S0
    $S0 = $P0[0]
    print "Unhandled exception: "
    print $S0
    print "\n"
    exit 1

I already sent this to Klaas-Jan Stol <[EMAIL PROTECTED]> ,
but when I didn't get a reply or see the change in svn after
a few days, I RTFM'd on contributing patches.

Cheers,
Julian

--- languages/lua/Lua/pir.pm    2007-03-07 16:26:54.000000000 +0900
+++ languages/lua/Lua/pir.pm    2007-03-07 16:26:49.000000000 +0900
@@ -22,6 +22,7 @@
   $P0 = new .Array
   set $P0, $I0
   $I1 = 0
+  push_eh root_exception_handler
 L1:
   unless $I1 < $I0 goto L2
   $S0 = shift args
@@ -43,7 +44,16 @@
   load_bytecode 'languages/lua/lib/luaos.pbc'
   load_bytecode 'languages/lua/lib/luadebug.pbc'
   load_bytecode 'languages/lua/lib/luaperl.pbc'
-  _main($P0 :flat)
+  .return _main($P0 :flat)
+ 
+  # a convenient place?
+root_exception_handler:
+  get_results '(0, 0)', $P0, $S0
+  $S0 = $P0[0]
+  print "Unhandled exception: "
+  print $S0
+  print "\n"
+  exit 1
 .end
 
 .sub '__onload' :anon :init
Index: CREDITS
===================================================================
--- CREDITS     (revision 17374)
+++ CREDITS     (working copy)
@@ -313,6 +313,9 @@
 N: Juergen Boemmels
 D: Parrot I/O; macro stuff in assembler.
 
+N: Julian Fondren
+E: [EMAIL PROTECTED]
+
 N: Karl Forner
 D: shootout examples testing
 E: [EMAIL PROTECTED]