server-local variables

[Michael Albinus <michael.albinus@gmx.de>]

Hi,

a long standing wishlist for Tramp are server-local (sometimes called
connection-local) variables. It was expressed for the first time in
<https://debbugs.gnu.org/cgi/bugreport.cgi?bug=3736#35>, but there are
more discussions about in bug reports and discussions on emacs-devel and
tramp-devel.

I'm playing with a small patch for files.el, which provides a mechanism
similar to directory-local variables. Most important are the following
functions:

--8<---------------cut here---------------start------------->8---
server-locals-set-class is a compiled Lisp function in
‘../../../src/emacs/lisp/files.el’.

(server-locals-set-class REGEXP CLASS)

Add CLASS for remote servers.
REGEXP is a regular expression identifying remote servers, a string.
CLASS is the name of a project class, a symbol.

When a connection to a remote server is opened, the
server-specific variables from CLASS are applied to the
corresponding process buffer.  The variables for a class are
defined using ‘server-locals-set-class-variables’.
--8<---------------cut here---------------end--------------->8---

--8<---------------cut here---------------start------------->8---
server-locals-set-class-variables is a compiled Lisp function in
‘../../../src/emacs/lisp/files.el’.

(server-locals-set-class-variables CLASS VARIABLES)

Map the symbol CLASS to a list of variable settings.
VARIABLES is a list that declares server-local variables for the
class.  An element in VARIABLES is an alist whose elements are of
the form (VARIABLE . VALUE).

When a connection to a remote server is opened, the server’s
classes are found.  A server may be assigned a class using
‘server-locals-set-directory-class’.  Then variables are set in
the server’s process buffer according to the VARIABLES list of
the class.  The list is processed in order.
--8<---------------cut here---------------end--------------->8---

--8<---------------cut here---------------start------------->8---
hack-server-local-variables-apply is a compiled Lisp function in
‘../../../src/emacs/lisp/files.el’.

(hack-server-local-variables-apply)

Apply server-local variables for the server identified by ‘default-directory’.
Other local variables, like file-local and dir-local variables,
will not be touched.
--8<---------------cut here---------------end--------------->8---

With these functions, one could write the following code snippet,
pushing a server-local variable `some-useful-setting' for all remote
connections using the "sudo" method:

--8<---------------cut here---------------start------------->8---
(server-locals-set-class-variables
 'remote '((some-useful-setting . some-useful-value)))

(server-locals-set-class "^/sudo:" 'remote)

;; This must be applied in a buffer with remote `default-directory'.
(hack-server-local-variables-apply)
--8<---------------cut here---------------end--------------->8---

Comments?

Best regards, Michael.