bug#61394: 30.0.50; [PATCH] Image-dired thumb name based on content

[Manuel Giraud via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

[...]

>> Yes I think it does.  My patch for bug#61394 changes the previous
>> behaviour of 'image-dired-thumbnail-storage'.  Now
>> 'image-dired-thumbnail-storage' defines where (ie. in which directory)
>> the thumbnails are stored and I introduce 'image-dired-thumb-naming'
>> which tells how thumbnail file ared named (ie. the file name part sans
>> directory).
>> 
>> 'image-dired-thumb-naming' is meaning less if
>> 'image-dired-thumbnail-storage' is one of the "standard*" method because
>> those methods already define storage locations, file names and even
>> sizes.  But for the "per-directory" method, I'm using
>> 'image-dired-thumb-naming'.  As we are talking about thumbnail I did not
>> think it was a big deal but if it is I can prepare a patch, on top of
>> the one in place, and then 'image-dired-thumb-naming' will be used only
>> for the "image-dired" storage method.  WDYT?
>
> I don't think I understand all the aspects of this, as I use neither
> image-dired nor the thumbnails.  But it sounds like an incompatible
> change in behavior wrt what we have in Emacs 29?  If so, how do we
> expect this to work for users who will have configured their Emacs for
> some particular storage type, and then upgrade to Emacs 30 when that
> is released?  Will the existing thumbnails still work for them?  Will
> Emacs 30 now start storing thumbnails under differently-formatted
> names, even though the user didn't change his/her configuration?

AFAIU image-dired thumbnails' generation, this will automatically work
for users from Emacs 29... but you are right that new thumbnails (with
new names) will be generated.  This will be true for users of the
"per-directory" storage method.  This will also be true when one user
customize the 'image-dired-thumb-naming' to 'sha1-contents'.

> In general, any incompatible change in behavior (if there is indeed
> such a change caused by this changeset) is undesirable.  So I'd like
> first to discuss why there was a need for the behavior change in the
> first place.

If you talk about the behaviour change for the "per-directory" method,
as I said, I can restore it back to what it was.
-- 
Manuel Giraud