bug#69517: [PATCH] Make gnus cache work with group names having '/'

[Eli Zaretskii <eliz@gnu.org>]

Ping! Is there anything else left to be done here, or should we close
this?

> From: Daniel Semyonov <daniel@dsemy.com>
> Cc: 69517@debbugs.gnu.org,  Eric Abrahamsen <eric@ericabrahamsen.net>,  Eli
>  Zaretskii <eliz@gnu.org>
> Date: Fri, 15 Mar 2024 19:33:42 +0200
> 
> >>>>> James Thomas writes:
> 
>     > Eric Abrahamsen wrote:
>     >> The real problem (well, one of the real problems) is that we should just
>     >> have two central routines for reading and writing active files, so that
>     >> there are only two places to keep in sync. Instead we have those two
>     >> places, and then a smattering of other functions in other places that do
>     >> something similar, and also have to be kept in sync, and I haven't done
>     >> that. At the very least I'll need to apply your patch from 65467.
>     >> 
>     >> The other real problem is that gnus-cache is confused about whether it
>     >> wants to be a select method, or a modified version of article saving.
>     >> The presence of `gnus-use-long-file-name' indicates the latter, but the
>     >> manual's instructions about the nnml select method indicates the former.
>     >> 
>     >> I think it should be a select method, which means that the group
>     >> directory should be created in "News/cache" the same way it is created
>     >> at the top level: with the "/" replaced by "_", and everything else
>     >> using the proper "left/right" group name. Perhaps "long file names" can
>     >> still play a role, but if so that should be via
>     >> `nnmail-use-long-file-names', and gnus-cache in general should behave
>     >> like a nnmail backend.
> 
>     > Well, I have sort of, an approach based on my earlier patch: [patch]
> 
>     > James Thomas wrote:
> 
>     >> +	(if (not nnmail-use-long-file-names)
>     >> +            (nnheader-replace-chars-in-string group ?. ?/)
>     >> +	  group))
> 
>     > Since directory names cannot have '/' they used to be replaced by '_' in
>     > group names before conversion. But this makes it impossible, when
>     > generating (non-existent) active files to know whether a '_' in the
>     > directory name was _ or / originally.
> 
>     > The above patch tries a possible solution inspired from [1] but would
>     > break existing users of the cache or agent (xref-find-references
>     > "nnmail-group-pathname") who have groups with % or / in their names.
> 
>     > Seems to work in my limited testing. WDYT?
> 
> I tested it and it seems to work, but I'm pretty sure it will also break
> existing groups with % or / in their names in several backends.
> For example, the `nnmh' and `nndiary' backends use this function to
> locate groups on disk, which will fail for those groups (unless users
> rename the files manually).
> 
> FWIW I think this approach is good, but since Gnus doesn't even emit a
> warning currently when creating a group with % in its name, I don't
> think breaking these groups is a good idea.
> 
> Daniel
>