On 11/6/2021 10:41 AM, Michael Albinus wrote:
> The general rule is, to keep all this specific handling away from
> files.el and companions. Emacs has the concept of file name handlers,
> and if there is something to be done special, a file name handler shall
> offer an alternative implementation. 

Thanks for the pointers. I've attached a new version of the patch, along 
with updated benchmark results. When abbreviating Tramp files, not only 
is this version faster than my previous patch, it's also 2-4x faster(!) 
than Emacs trunk.

I included a couple of related patches in this series, although I can 
split them out if it would be easier. The first patch just reorders a 
couple of Tramp tests that got added in the wrong order previously (I 
only did this because I wanted to add my new test to the end, and 
figured it would be simpler to fix the order first).

The second patch is the main patch and uses a file name handler as you 
suggested. Hopefully I got everything right here; I'm not very familiar 
with these parts of Tramp. The test I added passes for me, though a 
bunch of the other Tramp tests fail for me (with or without my patches).

Finally, since I already had them lying around, I added a few tests for 
`abbreviate-file-name' for local files. They're pretty simple, but 
should help catch any regressions in the future.