$ emacs -Q M-: (abbreviate-file-name "/home/jim/src") RET ;; => "~/src" M-: (abbreviate-file-name "/sshx:localhost:/home/jim/src") RET ;; => "/sshx:localhost:/home/jim/src"It'd be nice to abbreviate TRAMP home dirs, especially for the buffer list, where the long length of TRAMP paths means that I often just see the same leading bits of the paths repeated in the File column. As a result, it can be hard to tell the exact file it refers to. (Of course, as a workaround, I could just widen the window.)
Attached is a patch series to do this, but the patches probably warrant some explanation. First, I removed `automount-dir-prefix'; it's been obsolete since 24.3, and it would have made implementation of the second part more complex.
Second, I removed the caching of the abbreviated home dir. Since adding TRAMP support means there are multiple home dirs (one per host), keeping the caching would have been fairly complex, and it's already the source of potential bugs (e.g. when temporarily setting HOME to something else). I did some benchmarking on this (see attached), and while it is indeed slower without the caching, I don't think it's worth keeping the caching around. The real performance cost comes from calling `abbreviate-file-name' with a TRAMP file (even before my patch), but abbreviating a local file is quite fast, even with a pathologically large `directory-abbrev-alist'. I also wrote a couple of unit tests to make sure this function works correctly.
Finally, I added the actual TRAMP support. This has a pretty significant performance hit to TRAMP files. Looking at profiles, this appears to be because my patch calls both `file-name-case-insensitive-p' and `file-remote-p' on the TRAMP path, and these duplicate quite a bit of work. Is there a way to make this more efficient (e.g. by getting the file handler just once instead of twice)? It might also be useful to add some unit tests here, but I wasn't 100% sure how to do that with TRAMP paths (the tests in my benchmark actually open an SSH connection, so that probably won't work on all systems).
In addition to the patches, I've also attached a simple benchmark script that I used to measure the performance of these patches as well as the results from my system. The performance for local paths is still quite good I think, and even the worst-case scenario for TRAMP paths (abbreviating with a 500-item `directory-abbrev-alist') clocks in at 4.6ms per call. It'd be nice to make that faster, but maybe that's the best we can do if we want this feature.
0001-Remove-automount-dir-prefix.patch
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0002-Don-t-cache-abbreviated-homedir-for-abbreviate-file-.patch
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0003-Abbreviate-home-directory-for-remote-files.patch
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benchmark.el
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benchmark-results.txt
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