bug#51622: 29.0.50; [PATCH v3] Abbreviate remote home directories in `abbreviate-file-name'

[Jim Porter]

On 11/14/2021 6:43 AM, Michael Albinus wrote:
> Thanks. However, I believe this test shall be called
> `files-tests-file-name-non-special-file-abbreviate-file-name', like the
> other non-special tests. And perhaps it shall be located prior
> `files-tests-file-name-non-special-access-file'.

Ok, done.

> > Incidentally, another interesting
> > feature would be abbreviating default methods/users. That's probably
> > easy when Tramp has filled in those values since the file name has
> > `tramp-default' properties set. I'm not sure how tricky it would be to
> > do without those properties though.
>
> You cannot trust the `tramp-default' property. It is set when a method
> or user or host name is expanded as in "/ssh::". But when the host name
> is used explicitly by the user, as in "/ssh:host:", the property is not
> set, even if "host" is the default. Same for user.
>
> But it shouldn't be too hard to determine the defaults. We have
> tramp-default-method{-alist}, tramp-default-user{-alist}, and
> tramp-default-host{-alist}. All needed information is there.

Right, that confirms what I suspected. I'll try to look into this in 
more detail later when I get the chance.

> > I also attached a slightly-updated benchmark script as well as new
> > results. Performance on local file names is the same as before the
> > patch, and just slightly faster than before with Tramp file
> > names. (Most of the performance improvements here happened in
> > bug#51699, so I mainly wanted to maintain the current performance in
> > this patch.)
>
> Good, no regression :-)

Fixing your comments below *did* regress performance for abbreviating 
Tramp file names compared to current master (it takes 1.47x as long now 
in the worst case), but it's still considerably faster than Emacs 28. 
I've attached updated benchmark results to show the difference.

> This shall be rather "---". We don't add documentation (yet) for this
> new Tramp feature.

Fixed.

> > +*** Tramp supports abbreviating remote home directories now.
> > +When calling 'abbreviate-file-name' on a Tramp filename, the result
> > +will abbreviate the home directory to "~".
>
> This might be misleading. ... the result will abbreviate the remote home
> directory to "/ssh:user@host:~" (for example).

Ok, I tried to make this section clearer.

> Well, I believe we can implement abbreviation also for other Tramp
> backends, like in tramp-sudoedit.el. So it might be better to call this
> handler `tramp-handle-abbreviate-file-name'.

Done. I added this for the sudoedit and smb methods, since both support
"~" expansion in `expand-file-name'. That *should* be sufficient, but 
I've never used either of those methods, so I could be wrong...

> Please use `case-insensitive-p'. We don't know whether there will be
> other implementation for this magic function in the future. And we shall
> not bypass the checks in `tramp-file-name-handler', which are important
> for parallel invocations of Tramp handlers.

Fixed (same with `expand-file-name'). These changes slow things down a 
fair bit, but that's mostly due to checking for the right file name 
handler more often. Like I said above though, it's still a lot faster 
than Emacs 28 (thanks to bug#51699).

0001-Add-another-abbreviate-file-name-test.patch
Description: Text document

0002-Support-abbreviating-home-directory-of-Tramp-filenam.patch
Description: Text document

benchmark-results.txt
Description: Text document