Re: master c5cf630: Don't clobber match data in utf-8-hfs conversion (bug#41445)

Re: master c5cf630: Don't clobber match data in utf-8-hfs conversion (bug#41445)

[Stefan Monnier]

>  ;; Pre-write conversion for `utf-8-hfs'.
>  ;; _from and _to are legacy arguments (see `define-coding-system').
>  (defun ucs-normalize-hfs-nfd-pre-write-conversion (_from _to)
> -  (ucs-normalize-HFS-NFD-region (point-min) (point-max)))
> +  (save-match-data
> +    (ucs-normalize-HFS-NFD-region (point-min) (point-max))))

IIUC this is needed because `(en|de)code-coding-string`  is not supposed
to touch the match-data, right?

If so, I think we should do two things:

1- document that `(en|de)code-coding-string` preserve the match-data.
2- document in `define-coding-system` that the pre/post-conversion
   functions should preserve the match-data.

WDYT?


        Stefan

Re: master c5cf630: Don't clobber match data in utf-8-hfs conversion (bug#41445)

[Mattias Engdegård]

28 maj 2020 kl. 15.40 skrev Stefan Monnier <monnier@iro.umontreal.ca>:

> 1- document that `(en|de)code-coding-string` preserve the match-data.
> 2- document in `define-coding-system` that the pre/post-conversion
>   functions should preserve the match-data.

Very reasonable; now done on master.
We could perhaps say the same thing about {en,de}code-coding-region but I didn't do that in this change.

Re: master c5cf630: Don't clobber match data in utf-8-hfs conversion (bug#41445)

[Stefan Monnier]

>> 1- document that `(en|de)code-coding-string` preserve the match-data.
>> 2- document in `define-coding-system` that the pre/post-conversion
>>   functions should preserve the match-data.
>
> Very reasonable; now done on master.
> We could perhaps say the same thing about {en,de}code-coding-region but
> I didn't do that in this change.

`(en|de)code-coding-region` run various other (buffer-modification)
hooks, so I don't think anyone currently relies on them preserving the
match-data (and it would be a wrong assumption), also because those
function can change buffer positions making the match-data invalid even
if it's not modified.  So I don't see any need to declare that those
functions preserve the match-data.


        Stefan