bug#14724: 24.3.50; `isearch-open-necessary-overlays' handling of overlay property 'isearch-open-invisible'

bug#14724: 24.3.50; `isearch-open-necessary-overlays' handling of overlay property 'isearch-open-invisible'

[Drew Adams]

The code would be more robust if it would gracefully handle (1) an
non-functional value and perhaps also (2) a functional value where
invoking the function raises an error.  Here is the problematic code:

(funcall (overlay-get ov 'isearch-open-invisible)  ov)

For (1), the code could be like this:

(when (functionp (overlay-get ov 'isearch-open-invisible))
  (funcall (overlay-get ov 'isearch-open-invisible) ov))

For (1+2), that could be wrapped in `ignore-errors'.  Dunno whether (2)
is an important case to handle or whether it is really advisable to
ignore such an error.

Handling (1) seems to me reasonable, and with no downside.  The behavior
is to just do nothing additional with the overlay - e.g., leave the text
invisible.

Dunno know whether similar considerations apply to
`isearch-open-invisible-temporary'.  I'm guessing no - its value seems
to be provided only by the Isearch code (whereas code far from Isearch
sets the `isearch-open-invisible' overlay property).

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-06-20 on ODIEONE
Bzr revision: 113100 eliz@gnu.org-20130620173624-w9v620tog4yacftk
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 CFLAGS=-O0 -g3 LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'

bug#14724: 24.3.50; `isearch-open-necessary-overlays' handling of overlay property 'isearch-open-invisible'

[Stefan Monnier]

> The code would be more robust if it would gracefully handle (1) an
> non-functional value and perhaps

Wouldn't such a non-function non-nil value reflect an error in an
Elisp package?  If so, why should we silence it?

> For (1+2), that could be wrapped in `ignore-errors'.

I thing I disagree with ignore-errors here (at least, I don't think such
errors are normal, so they shouldn't be silenced), but using
with-demoted-errors could make sense if errors in this code could make
isearch non-functional.  Is that the case?


        Stefan

bug#14724: 24.3.50; `isearch-open-necessary-overlays' handling of overlay property 'isearch-open-invisible'

[Drew Adams]

> > The code would be more robust if it would gracefully handle (1) an
> > non-functional value and perhaps
> 
> Wouldn't such a non-function non-nil value reflect an error in an
> Elisp package?

Yes, normally.  In Elisp code, whether a package or not, and whether distributed by Emacs Dev or not.

> If so, why should we silence it?

It would allow 3rd-party code that might not be correct in this regard to at least allow Isearch to continue to function normally otherwise.

The only reasonable value is a function, since we immediately invoke funcall with it.  I'm guessing it might not be obvious to someone where the error lies.

It costs nothing for the code to protect itself from funcalling a non-function here and thus fail gracefully with a no-op.  Someone trying to use this feature will as likely dig in to figure out the problem with a non-action as with an error, but users would at least not be impacted.

Of course I agree that raising an error for incorrect code is typically TRT.  I'm not sure it is in this case.  See what I said about `isearch-open-invisible-temporary', which is different in that it is not set up in distant code but is internal to isearch.el.

> > For (1+2), that could be wrapped in `ignore-errors'.
> 
> I thing I disagree with ignore-errors here (at least, I don't think such
> errors are normal, so they shouldn't be silenced), but using
> with-demoted-errors could make sense if errors in this code could make
> isearch non-functional.  Is that the case?

An error is raised; that's all - Isearch is not broken by it.  Yes, `with-demoted-errors' makes more sense.  The same considerations apply here as for a non-function: better a no-op (a msg is OK) than an error, I think.

Whatever you decide is fine with me.  I'm essentially bringing it to your attention.  Perhaps Juri has some input on this?

bug#14724: 24.3.50; `isearch-open-necessary-overlays' handling of overlay property 'isearch-open-invisible'

[Stefan Monnier]

tags 14724 notabug
thanks

> An error is raised; that's all - Isearch is not broken by it.  Yes,

Then there's no point adding a with-demoted-error.


        Stefan