Extend signal-process and proced.el

* doc/lispref/processes.texi (Signals to Processes):
Document changes in signal-process.

* etc/NEWS: Mention changes in proced.el and signal-process.

* lisp/proced.el (proced-signal-function): Declare it obsolete.
(proced-remote-directory): New user option.
(proced-mode): Adapt docstring.
(proced-send-signal, proced-renice): Handle interactive prefix argument.

* lisp/net/tramp.el (tramp-signal-process): New defun.  Add it to
`signal-process-functions'.

* src/process.c (Finternal_default_signal_process): New defun,
providing the hitherto existing implementation of Fsignal_process.
(Fsignal_process): Loop through Vsignal_process_functions.
(Vsignal_process_functions): New defvar.
(Qinternal_default_signal_process, Qsignal_process_functions):
Declare symbols.
(Sinternal_default_signal_process): Declare subroutine.

* test/lisp/net/tramp-tests.el (tramp-test31-signal-process): New test.

2 files changed, 70 insertions, 11 deletions

diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 4e5eed9d997..bddbe3f91a2 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -5961,6 +5961,45 @@ name of a process or buffer, or nil to default to the current buffer."
  (lambda ()
    (remove-hook 'interrupt-process-functions #'tramp-interrupt-process)))
 
+(defun tramp-signal-process (process sigcode &optional remote)
+  "Send PROCESS the signal with code SIGCODE.
+PROCESS may also be a number specifying the process id of the
+process to signal; in this case, the process need not be a child of
+this Emacs.
+If PROCESS is a process object which contains the property
+`remote-pid', or PROCESS is a number and REMOTE is a remote file name,
+PROCESS is interpreted as process on the respective remote host, which
+will be the process to signal.
+SIGCODE may be an integer, or a symbol whose name is a signal name."
+  (let (pid vec)
+    (cond
+     ((processp process)
+      (setq pid (process-get process 'remote-pid)
+            vec (process-get process 'vector)))
+     ((numberp process)
+      (setq pid process
+            vec (and (stringp remote) (tramp-dissect-file-name remote))))
+     (t (signal 'wrong-type-argument (list #'processp process))))
+    (unless (or (numberp sigcode) (symbolp sigcode))
+      (signal 'wrong-type-argument (list #'numberp sigcode)))
+    ;; If it's a Tramp process, send SIGCODE remotely.
+    (when (and pid vec)
+      (tramp-message
+       vec 5 "Send signal %s to process %s with pid %s" sigcode process pid)
+      ;; This is for tramp-sh.el.  Other backends do not support this (yet).
+      (if (tramp-compat-funcall
+           'tramp-send-command-and-check
+           vec (format "\\kill -%s %d" sigcode pid))
+          0 -1))))
+
+;; `signal-process-functions' exists since Emacs 29.1.
+(when (boundp 'signal-process-functions)
+  (add-hook 'signal-process-functions #'tramp-signal-process)
+  (add-hook
+   'tramp-unload-hook
+   (lambda ()
+     (remove-hook 'signal-process-functions #'tramp-signal-process))))
+
 (defun tramp-get-remote-null-device (vec)
   "Return null device on the remote host identified by VEC.
 If VEC is `tramp-null-hop', return local null device."
diff --git a/lisp/proced.el b/lisp/proced.el
index c1d599afc4a..7966ccfb084 100644
--- a/lisp/proced.el
+++ b/lisp/proced.el
@@ -29,10 +29,6 @@
 ;;
 ;; To do:
 ;; - Interactive temporary customizability of flags in `proced-grammar-alist'
-;; - Allow "sudo kill PID", "sudo renice PID"
-;;   `proced-send-signal' operates on multiple processes one by one.
-;;   With "sudo" we want to execute one "kill" or "renice" command
-;;   for all marked processes.  Is there a `sudo-call-process'?
 ;;
 ;; Thoughts and Ideas
 ;; - Currently, `process-attributes' returns the list of
@@ -61,6 +57,14 @@ It can be an elisp function (usually `signal-process') or a string specifying
 the external command (usually \"kill\")."
   :type '(choice (function :tag "function")
                  (string :tag "command")))
+(make-obsolete-variable 'proced-signal-function "no longer used." "29.1")
+
+(defcustom proced-remote-directory "/sudo::"
+  "Remote directory to be used when sending a signal.
+It must point to the local host, via a `sudo' or `doas' method,
+or alike.  See `proced-send-signal' and `proced-renice'."
+  :version "29.1"
+  :type '(string :tag "remote directory"))
 
 (defcustom proced-renice-command "renice"
   "Name of renice command."
@@ -626,6 +630,9 @@ Return nil if point is not on a process line."
 Type \\[proced] to start a Proced session.  In a Proced buffer
 type \\<proced-mode-map>\\[proced-mark] to mark a process for later commands.
 Type \\[proced-send-signal] to send signals to marked processes.
+Type \\[proced-renice] to renice marked processes.
+With a prefix argument \\[universal-argument], sending signals to and renicing of processes
+will be performed with the credentials of `proced-remote-directory'.
 
 The initial content of a listing is defined by the variable `proced-filter'
 and the variable `proced-format'.
@@ -1766,7 +1773,10 @@ runs the normal hook `proced-after-send-signal-hook'.
 For backward compatibility SIGNAL and PROCESS-ALIST may be nil.
 Then PROCESS-ALIST contains the marked processes or the process point is on
 and SIGNAL is queried interactively.  This noninteractive usage is still
-supported but discouraged.  It will be removed in a future version of Emacs."
+supported but discouraged.  It will be removed in a future version of Emacs.
+
+With a prefix argument \\[universal-argument], send the signal with the credentials of
+`proced-remote-directory'."
   (interactive
    (let* ((process-alist (proced-marked-processes))
           (pnum (if (= 1 (length process-alist))
@@ -1808,7 +1818,10 @@ supported but discouraged.  It will be removed in a future version of Emacs."
                                         proced-signal-list
                                         nil nil nil nil "TERM"))))))
 
-  (let (failures)
+  (let ((default-directory
+         (if (and current-prefix-arg (stringp proced-remote-directory))
+             proced-remote-directory temporary-file-directory))
+        failures)
     ;; Why not always use `signal-process'?  See
     ;; https://lists.gnu.org/r/emacs-devel/2008-03/msg02955.html
     (if (functionp proced-signal-function)
@@ -1821,7 +1834,8 @@ supported but discouraged.  It will be removed in a future version of Emacs."
           (dolist (process process-alist)
             (condition-case err
                 (unless (zerop (funcall
-                                proced-signal-function (car process) signal))
+                                proced-signal-function (car process) signal
+                                (file-remote-p default-directory)))
                   (proced-log "%s\n" (cdr process))
                   (push (cdr process) failures))
               (error ; catch errors from failed signals
@@ -1833,7 +1847,7 @@ supported but discouraged.  It will be removed in a future version of Emacs."
         (dolist (process process-alist)
           (with-temp-buffer
             (condition-case nil
-                (unless (zerop (call-process
+                (unless (zerop (process-file
                                 proced-signal-function nil t nil
                                 signal (number-to-string (car process))))
                   (proced-log (current-buffer))
@@ -1862,7 +1876,10 @@ PROCESS-ALIST is an alist as returned by `proced-marked-processes'.
 Interactively, PROCESS-ALIST contains the marked processes.
 If no process is marked, it contains the process point is on,
 After renicing all processes in PROCESS-ALIST, this command runs
-the normal hook `proced-after-send-signal-hook'."
+the normal hook `proced-after-send-signal-hook'.
+
+With a prefix argument \\[universal-argument], apply renice with the credentials of
+`proced-remote-directory'."
   (interactive
    (let ((process-alist (proced-marked-processes)))
      (proced-with-processes-buffer process-alist
@@ -1871,11 +1888,14 @@ the normal hook `proced-after-send-signal-hook'."
    proced-mode)
   (if (numberp priority)
       (setq priority (number-to-string priority)))
-  (let (failures)
+  (let ((default-directory
+         (if (and current-prefix-arg (stringp proced-remote-directory))
+             proced-remote-directory temporary-file-directory))
+        failures)
     (dolist (process process-alist)
       (with-temp-buffer
         (condition-case nil
-            (unless (zerop (call-process
+            (unless (zerop (process-file
                             proced-renice-command nil t nil
                             priority (number-to-string (car process))))
               (proced-log (current-buffer))