[Sbcl-devel] (update-class ...) bug

[kr <kr...@mo...>]

pcl has improved greatly in sbcl-0.8.0 . great !  thanx to all the
people who have been fixing this monster.

i did however run across another serious bug, which has been around
for countless years, and i think i fixed it.  it has to do with
forward-referenced classes and the class-precedence-list.

below is a test case that reproduces the break in sbcl-0.8.0 , and
after that is my little patch, that fixes this, at least for my
purposes.  note that i know next to nothing about pcl, so i have a
hard time understanding whether my fix might have some unintended
consequences somewhere deep in the guts of pcl.  but so far so good.
maybe some pcl gurus might want to give their blessings before it ends
up on sourceforge...



the bug:
-------------------------------------------------------------
* (defclass xyw (foo) (bar))

#<STANDARD-CLASS XYW>
* (describe *)


#<STANDARD-CLASS XYW> is a class, it is an instance of STANDARD-CLASS.
Its proper name is XYW.

debugger invoked on condition of type UNBOUND-SLOT:
  The slot SB-PCL:CLASS-PRECEDENCE-LIST is unbound in the object #<STANDARD-CLASS
                                                                   XYW>.

Within the debugger, you can type HELP for help. At any command prompt (within
the debugger or not) you can type (SB-EXT:QUIT) to terminate the SBCL
executable. The condition which caused the debugger to be entered is bound to
*DEBUG-CONDITION*. You can suppress this message by clearing
*DEBUG-BEGINNER-HELP-P*.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT   ] Reduce debugger level (leaving debugger, returning to toplevel).
  1: [TOPLEVEL] Restart at toplevel READ/EVAL/PRINT loop.
((SLOT-UNBOUND (T T T))
 #<unavailable argument>
 #<unavailable argument>
 #<unavailable argument>
 #<STANDARD-CLASS XYW>
 SB-PCL:CLASS-PRECEDENCE-LIST)
0] 
-------------------------------------------------------------





the fix, against sbcl-0.8.0 :
-------------------------------------------------------------

--- std-class.lisp.~1~	Mon May 19 05:14:02 2003
+++ std-class.lisp	Thu Jun 12 23:45:37 2003
@@ -904,6 +904,11 @@
     (update-inits class (compute-default-initargs class))
     (update-shared-slot-values class)
     (update-ctors 'finalize-inheritance :class class))
+  ;;kr030518: a newly created class with just a forward-referenced-superclass
+  ;; should not leave the class-precedence-list unbound.  so the following
+  ;; form was added to fix a long-standing bug.
+  (when (class-has-a-forward-referenced-superclass-p class)
+    (update-cpl class (list class)))
   (unless finalizep
     (dolist (sub (class-direct-subclasses class)) (update-class sub nil))))

-------------------------------------------------------------

-- 
regards
markus krummenacker