bug#19636: [TRAMP] global minor mode hangs connection when accessing files in :lighter

[Philippe Vaucher]

Hello,

TRAMP hangs the connection for any new processes in both emacs 24.4
and emacs from the master branch when a global minor mode uses a
:lighter which evals `(file-truename default-directory)`.

To reproduce:

M-x find-file buggy-tramp-mode.el
M-x eval-buffer
M-x global-buggy-tramp-mode
M-x find-file /scpx:user@host:/tmp/foo.txt
M-x async-shell-command ls

The last command (new process) doens't complete and the TRAMP buffer
shows "Are you awake?". My understanding of the problem is that
`file-truename` tries to use a not-yet-ready TRAMP connection. To work
around that was tried is to use `tramp-connectable-p` or even
`file-remote-p` with the appropriate flags, but they both
(incorrectly?) return true.

The "real world" issue that it affects is
https://github.com/bbatsov/projectile/issues/523

Please ask if I'm unclear or you need more clarifications.

Thanks,
Philippe

buggy-tramp-mode.el
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