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

[Eric Abrahamsen <eric@ericabrahamsen.net>]

James Thomas <jimjoe@gmx.net> writes:

> Eli Zaretskii wrote:
>
>>> Date: Sun, 03 Mar 2024 07:22:29 +0530
>>> From:  James Thomas via "Bug reports for GNU Emacs,
>>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>>>
>>> Tags: patch
>>>
>>> Reproduction steps:
>>>
>>> - Setup Gnus with any group name having a slash ('/') such as
>>>   "[Gmail]/Drafts" or an Atom feed (they usually have slashes) using the
>>>   patch in bug#66188.
>>>
>>> - Press '*' on a message in the group.
>>>
>>> - Do (info "(gnus) Creating a Virtual Server")
>>>
>>> - Open the above from the Server buffer; RET on the new group fails.
>>>
>>> A patch is attached. I couldn't find the problematic commit or its
>>> original branch (where it was a consolidated merge from) but
>>> 'gnus-use-long-file-names' is apparently not meant for backends: it
>>> can't even be customized with that 'not-cache' option. I think this is
>>> the right way to solve it: the other lines removed in this patch are
>>> even older, but they were never being called due to the above reason.
>>
>> Eric, could you please review the patch and install if it's okay?
>>
>> Thanks.
>
> There's a small caveat after applying this:
>
> Before this patch, cache entries would've effectively ignored
> 'nnmail-use-long-file-names' (nil by default) and used long names. After
> this patch new entries would honor it, resulting in an extra directory
> tree for the same group. But only the original one would be opened (due
> to [[./lisp/gnus/nnmail.el::;; If this direc]]). To fix it, one would
> have to copy all the files in from the original directory into the new
> one (and retain the active file entry). Or of course, change the above
> variable (but that could have other implications depending upon one's
> configuration).

Thanks for reporting this! Obviously something is wrong here, but I get
different results from your reproduction recipe (I'm running master):
when I create the cache nnml server and hit RET on it, I get:

K      1: nnml:left.right
K      1: nnml:left/right

I am able to subscribe to both groups. When I return to the *Group*
buffer, I can enter the version of the group with the ".", and read the
cached article, while attempting to enter the version with the slash
gives me "Invalid group (no such directory)".

On disk, the "News/cache/active" file starts out with the version with
the ".", and after I create the extra cache server it contains both, it
looks like:

"nnml:left.right" 1 1 y
"nnml:left/right" 1 1 y

Meanwhile, the directory structure "News/cache/nnml:left/right/1" is
created.

The "." in the active file comes from `gnus-cache-generate-active`, and
that mechanism seems to be working fine, at least in my case -- do you
not see that version of the group?

To be honest I have no idea what's happening in `gnus-cache-file-name'.
I'd be hesitant to remove all that code without understanding it better
And I don't think we can argue that that code is "dead" just because it
is behind an option value that isn't one of the customization options.

Anyway, it would be good to first know why you're not seeing the "."
version of the offending filename, and then I guess try to work out
what's going on with the file names. It kind of looks like a collision
between two different mechanisms -- one that translates "/" to "_" to
prevent unwanted filesystem hierarchies, and one that translates between
"/" and "." in order to convert newsgroup-name dot hierarchies into
filesystem hierarchies. In this case, it seems like "long names" and
newsgroup hierarchies shouldn't be applicable at all.

Eric