GNU bug report logs - #15103
Spurious "unused lexical argument" warning from condition-case

Previous Next

To add a comment to this bug, you must first unarchive it, by sending
a message to control AT debbugs.gnu.org, with unarchive 15103 in the body.
You can then email your comments to 15103 AT debbugs.gnu.org in the normal way.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3.50; Wrong byte compiler warning
Date: Thu, 15 Aug 2013 13:49:38 +0200

I have a file test.el:

(condition-case err
    (ignore)
  (file-error (ignore))
  (error (message "%s" (error-message-string err))))

When I compile it with --eval '(setq byte-compile-force-lexical-warnings t)'
I get the byte compiler warning

In toplevel form:
test.el:1:1:Warning: Unused lexical argument `err'
Wrote /home/albinus/tmp/test.elc

Note, that this warning does not appear when the first condition-case
handler does not exist.

Best regards, Michael.

Message #8 received at 15103 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 15103 <at> debbugs.gnu.org
Subject: Re: bug#15103: 24.3.50; Wrong byte compiler warning
Date: Thu, 15 Aug 2013 10:50:25 -0400

> I have a file test.el:
> (condition-case err
>     (ignore)
>   (file-error (ignore))
>   (error (message "%s" (error-message-string err))))

> When I compile it with --eval '(setq byte-compile-force-lexical-warnings t)'
> I get the byte compiler warning

> In toplevel form:
> test.el:1:1:Warning: Unused lexical argument `err'
> Wrote /home/albinus/tmp/test.elc

> Note, that this warning does not appear when the first condition-case
> handler does not exist.

Yup, same kind of problem as discussed in the "Cleaning up code" thread.
When compiling for lexical scoping, the condition case above gets turned
internally into something akin to:

 (condition-case :use-lexical-calling-convention
     (ignore)
   (file-error (lambda (err) (ignore)))
   (error (lambda (err) (message "%s" (error-message-string err)))))

so as you can see, we now have two separate declarations of `err' one of
which is unused.
There's a secondary bug as well in that the warning says "argument"
rather than "variable", but that's minor.


        Stefan

Message #13 received at 15103 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 15103 <at> debbugs.gnu.org
Subject: Re: bug#15103: 24.3.50; Wrong byte compiler warning
Date: Thu, 03 Oct 2013 23:41:50 -0400

> I have a file test.el:
> (condition-case err
>     (ignore)
>   (file-error (ignore))
>   (error (message "%s" (error-message-string err))))
[...]
> In toplevel form:
> test.el:1:1:Warning: Unused lexical argument `err'
> Wrote /home/albinus/tmp/test.elc

If you set byte-compile--use-old-handlers to nil, the above spurious
warning should now be fixed.


        Stefan

Message #16 received at 15103 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 15103 <at> debbugs.gnu.org
Subject: Re: bug#15103: 24.3.50; Wrong byte compiler warning
Date: Tue, 08 Oct 2013 11:35:03 +0200

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

> If you set byte-compile--use-old-handlers to nil, the above spurious
> warning should now be fixed.

That works, thanks. Shouldn't this be documented somewhere?

>         Stefan

Best regrads, Michael.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.