bug#15103: 24.3.50; Wrong byte compiler warning

bug#15103: 24.3.50; Wrong byte compiler warning

[Michael Albinus]

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.

bug#15103: 24.3.50; Wrong byte compiler warning

[Stefan Monnier]

> 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

bug#15103: 24.3.50; Wrong byte compiler warning

[Stefan Monnier]

> 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

bug#15103: 24.3.50; Wrong byte compiler warning

[Michael Albinus]

Stefan Monnier <monnier@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.