Make `signal-process' allow completing over signal names

* lisp/simple.el (read-signal-name): New function.
* src/process.c (Fsignal_process): Use it to allow completing over
the signal names (bug#56239).
(Fsignal_names): New function.

lisp/simple.el

@@ -10627,6 +10627,19 @@ If the buffer doesn't exist, create it first."
   "Check whether STRING is empty."
   (string= string ""))
 
+(defun read-signal-name ()
+  "Read a signal number or name."
+  (let ((value
+         (completing-read "Signal code or name: "
+                          (signal-names)
+                          nil
+                          (lambda (value)
+                            (or (string-match "\\`[0-9]+\\'" value)
+                                (member value (signal-names)))))))
+    (if (string-match "\\`[0-9]+\\'" value)
+        (string-to-number value)
+      (intern (concat "sig" (downcase value))))))
+
 
 
 (provide 'simple)

src/process.c

@@ -7109,7 +7109,7 @@ See function `signal-process' for more details on usage.  */)
 }
 
 DEFUN ("signal-process", Fsignal_process, Ssignal_process,
-       2, 3, "sProcess (name or number): \nnSignal code: ",
+       2, 3, "(list (read-string \"Process (name or number): \") (read-signal-name))",
        doc: /* 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
@@ -8317,6 +8317,22 @@ If QUERY is `all', also count processors not available.  */)
 #endif
 }
 
+DEFUN ("signal-names", Fsignal_names, Ssignal_names, 0, 0, 0,
+       doc: /* Return a list of known signal names on this system.  */)
+  (void)
+{
+  char name[SIG2STR_MAX];
+  Lisp_Object names = Qnil;
+  for (int i = 0; i < 255; ++i)
+    {
+      if (!sig2str (i, name))
+	{
+	  names = Fcons (build_string (name), names);
+	}
+    }
+  return names;
+}
+
 #ifdef subprocesses
 /* Arrange to catch SIGCHLD if this hasn't already been arranged.
    Invoke this after init_process_emacs, and after glib and/or GNUstep
@@ -8770,4 +8786,5 @@ sentinel or a process filter function has an error.  */);
   defsubr (&Slist_system_processes);
   defsubr (&Sprocess_attributes);
   defsubr (&Snum_processors);
+  defsubr (&Ssignal_names);
 }