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

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

Eli Zaretskii wrote:

> 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
>>

I've been using this since then, on master, with no problems. Let me add
to my earlier reasons for being confident about this not breaking
existing setups:

James Thomas wrote:

> I think only one of these combinations is likely to be a problem in
> practice: groups such as [Gmail]/Drafts. I've never seen a % in a
> group name. The cache wouldn't work for one with / anyway (this bug)
> and as far as the agent is concerned, none of the Gmail groups with
> spaces in them work anyway (bug#65467: note that the patch on this is
> also needed for the agent to work on these groups with /). I haven't
> used nnmh or nndiary but I don't think they normally use group names
> with '/'.

The only ones with '/' (and no spaces) I know of are the Gmail groups,
namely:

[Gmail]/Bin
[Gmail]/Drafts
[Gmail]/Important
[Gmail]/Spam
[Gmail]/Starred

...which are unlikely to be agentized because of their nature (though
ideally the patch at bug#65467 ought to be applied as well, after this).

Moreover, getting Gmail to work with Gnus requires a paid account and a
complicated setup with OAuth2 (AFAIK, because I use one) which only few
people are likely to have managed.

Lastly, the fix for such an unlikely existing setup is a simple rename
of the directory: say, from [Gmail]_Drafts to [Gmail]%2FDrafts.

Regards,
James