tramp (2.7.1.4 nil/nil); Tramp may attempt to create ControlPath sockets that exceed maximum path length

[Alex Hutcheson]

The ControlPath OpenSSH option specifies a path for a Unix domain
socket. On Linux, domain sockets have a much lower maximum path
length (currently 107 characters) than normal files.

By default, Tramp will create a ControlPath within
tramp-compat-temporary-file-directory. This path might be arbitrarily
long. This can cause the generated domain socket to have a length that
is too long, which causes the Tramp connection to fail. In this case,
the user sees an error like:

    unix_listener: path
    
"/usr/local/google/home/alexhutcheson/.cache/emacs/tramp.e49de70715dd5cc0f80403136e0beb44e47447f8.07oYPo8bGaOpL7Jr"
    too long for Unix domain socket

To reproduce:

1. Start Emacs using emacs -q

2. (setq tramp-compat-temporary-file-directory
"/tmp/some/extremely/long/path/to/reproduce/this/bug/")

3. Open a Tramp connection, e.g. C-x C-f /scp:some.remote.host.com:~

Workaround:

(setq tramp-compat-temporary-file-directory "/tmp/")


Emacs  : GNU Emacs 29.4 (build 1, x86_64-pc-linux-gnu, GTK+ Version  
3.24.41, cairo version 1.18.0)
 of 2024-06-28, modified by Debian
Package: tramp (2.7.1.4 nil/nil)