Re: default-component-class slot normally gets clobbered

Gary King <[email protected]> writes:
> On Jun 15, 2006, at 1:17 AM, Richard M Kreuter wrote:
>
>> While I don't find any uses of default-component-class by grepping
>> around the .asds I have, that's not conclusive...
>
> I think that the amount of code to be written far outweighs the  
> amount of existing code and that this implies that backwards  
> compatibility can be sacrificed in the name of progress. Perhaps a  
> putative patch could include code to warn if any systems are found  
> that rely on the old behavior...?

It's easy enough to warn in those cases where the proposed new
behavior might possibly make a difference (any module whose
default-component-class is bound and not nil at the end of
reinitialize-instance).

Unfortunately, if the system class is to have an initform for the
default-component-class slot, then this warning will be issued at
least for all direct instances of system, which means one such warning
will be raised for nearly all systems.

It's somewhat more aesthetic to have the system class have an initform
there than not, as it's hardly obvious that the
default-component-class slot is nearly always nil, and that the
defaulting inside class-for-type is responsible the correct
functioning of almost all extant systems.

Although I raised the possiblity that the fix I proposed would break
something, I did so only out of due diligence.  Remember that it
breaks only systems where somebody (a) deliberately added either a
class with an initform for the slot or a method on one of the
initializers to write the slot, and (b) never noticed that (a) had no
effect.  Is it possible?  Is it likely?  Is it worth caring about?

The following is a patch that both emits the warning and supplies the
initform for systems (and therefore emits the warning for every
system).

--
RmK

diff -u /home/kreuter/lsp/pkg/cclan/asdf/asdf.lisp /home/kreuter/lsp/pkg/cclan/asdf/asdf.lisp.dcc1
--- /home/kreuter/lsp/pkg/cclan/asdf/asdf.lisp	2006-06-15 22:30:13.000000000 -0400
+++ /home/kreuter/lsp/pkg/cclan/asdf/asdf.lisp.dcc1	2006-06-15 23:07:57.000000000 -0400
@@ -242,7 +242,7 @@
 			   :accessor module-if-component-dep-fails
 			   :initarg :if-component-dep-fails)
    (default-component-class :accessor module-default-component-class
-     :initform 'cl-source-file :initarg :default-component-class)))
+     :initarg :default-component-class)))
 
 (defgeneric component-pathname (component)
   (:documentation "Extracts the pathname applicable for a particular component."))
@@ -285,7 +285,8 @@
     :accessor system-long-description :initarg :long-description)
    (author :accessor system-author :initarg :author)
    (maintainer :accessor system-maintainer :initarg :maintainer)
-   (licence :accessor system-licence :initarg :licence)))
+   (licence :accessor system-licence :initarg :licence)
+   (default-component-class :initform 'cl-source-file)))
 
 ;;; version-satisfies
 
@@ -994,10 +995,19 @@
 	     :parent parent
 	     other-args)
       (when (typep ret 'module)
-	(setf (module-default-component-class ret)
-	      (or default-component-class
-		  (and (typep parent 'module)
-		       (module-default-component-class parent))))
+	(if (and (slot-boundp ret 'default-component-class)
+		 (not default-component-class))
+	    ;; This test and warning should go away eventually.
+	    (when (and (module-default-component-class ret)
+		       (not (typep ret 'system)))
+	      (warn "Honoring default-component-class ~A of ~A.~%~
+ASDF versions prior to 1.98 always overwrote this slot during
+system initialization."
+		    (module-default-component-class ret) ret))
+	    (setf (module-default-component-class ret)
+		(or default-component-class
+		    (and (typep parent 'module)
+			 (module-default-component-class parent)))))
 	(let ((*serial-depends-on* nil))
 	  (setf (module-components ret)
 		(loop for c-form in components

Diff finished.  Thu Jun 15 23:08:06 2006