GNU bug report logs - #45795
27.1; prolog-mode prolog-system switch bug

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: k3tu0isui <at> gmail.com
To: bug-gnu-emacs <at> gnu.org
Subject: 27.1; prolog-mode prolog-system switch bug
Date: Mon, 11 Jan 2021 22:39:22 +0530

[Message part 1 (text/plain, inline)]

Switching between prolog systems is not supported properly.

Say I stated with (setq prolog-system 'swi) in my configuration, and I set (setq-local prolog-system 'gnu) in my working buffer. Now when I do `run-prolog` it is expected to run gprolog instead of swipl. But this is not happening, it still runs swipl.

The bug seems to be in `prolog-ensure-process` function. If the process is not running, a new process is created using make-comint-in-buffer whose program name is supplied using (prolog-program-name). But we have already shifted to the *prolog* buffer here, so whatever the value of prolog-system in our source buffer, the program started is still that of the global variable.

In my patch I just bound (prolog-program-name) and (prolog-program-switches) before switching to *prolog* buffer. This seems to work.

[0001-prolog-mode-prolog-system-switch-process-bug.patch (text/plain, attachment)]

Message #8 received at 45795 <at> debbugs.gnu.org (full text, mbox):

From: k3tu0isui <at> gmail.com
To: 45795 <at> debbugs.gnu.org
Subject: bug#45795: prolog-mode prolog-system switch bug - also with run-prolog
Date: Tue, 12 Jan 2021 20:10:44 +0530

I have also noticed that this affects the `run-prolog` function in a way not affected by my previous patch.
In `run-prolog` function `prolog-ensure-process` is called after switching to the *prolog* buffer using `prolog-goto-prolog-process-buffer`. So my previous patch which deals with `prolog-ensure-process` will not affect this. I do not know how to rectify this due to the presence of SICStus-Prolog specific code that seems to be working in *prolog* buffer. If I moved `prolog-ensure-process` call before switching to *prolog* buffer, something SICStus might break. I have never worked with SICStus so I am not sure how to deal with this.

Message #11 received at 45795 <at> debbugs.gnu.org (full text, mbox):

From: k3tu0isui <at> gmail.com
To: 45795 <at> debbugs.gnu.org
Subject: [PATCH] prolog-mode run-prolog and prolog-consult-file fixes when
 prolog-system changes
Date: Tue, 12 Jan 2021 20:43:25 +0530

[Message part 1 (text/plain, inline)]

Can someone working with SICStus check if this patch breaks debugger(or anything) when `run-prolog` is used?

I have repeatedly checked switching between GNU-Prolog and SWI-Prolog systems after setting `prolog-system` to buffer local values 'gnu' and 'swi' resp.
Both `prolog-consult-file` and `run-prolog` are now starting the correct interpreter.

[Message part 2 (text/plain, inline)]

diff --git a/lisp/progmodes/prolog.el b/lisp/progmodes/prolog.el
index 9f5f9ed6d3..00d865af1a 100644
--- a/lisp/progmodes/prolog.el
+++ b/lisp/progmodes/prolog.el
@@ -1316,6 +1316,7 @@ run-prolog
       (progn
         (process-send-string "prolog" "halt.\n")
         (while (get-process "prolog") (sit-for 0.1))))
+  (prolog-ensure-process)
   (let ((buff (buffer-name)))
     (if (not (string= buff "*prolog*"))
         (prolog-goto-prolog-process-buffer))
@@ -1325,7 +1326,6 @@ run-prolog
              prolog-use-sicstus-sd)
         (prolog-enable-sicstus-sd))
     (prolog-mode-variables)
-    (prolog-ensure-process)
     ))
 
 (defun prolog-inferior-guess-flavor (&optional ignored)
@@ -1350,7 +1350,9 @@ prolog-ensure-process
   "If Prolog process is not running, run it.
 If the optional argument WAIT is non-nil, wait for Prolog prompt specified by
 the variable `prolog-prompt-regexp'."
-  (if (null (prolog-program-name))
+  (let ((pname (prolog-program-name))
+        (pswitches (prolog-program-switches)))
+    (if (null pname)
         (error "This Prolog system has defined no interpreter."))
     (if (comint-check-proc "*prolog*")
         ()
@@ -1368,7 +1370,7 @@ prolog-ensure-process
 		   process-environment
 	         (cons "INFERIOR=yes" process-environment))))
 	  (apply 'make-comint-in-buffer "prolog" (current-buffer)
-	       (prolog-program-name) nil (prolog-program-switches)))
+	         pname nil pswitches))
 
         (unless prolog-system
           ;; Setup auto-detection.
@@ -1399,7 +1401,7 @@ prolog-ensure-process
                      (re-search-backward
                       (concat "\\(" (prolog-prompt-regexp) "\\)" "\\=")
                       nil t)))
-              (sit-for 0.1)))))))
+                (sit-for 0.1))))))))
 
 (defun prolog-inferior-buffer (&optional dont-run)
   (or (get-buffer "*prolog*")

[prolog-switch-final.diff (text/plain, attachment)]

Message #16 received at 45795 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: k3tu0isui <at> gmail.com
Cc: 45795 <at> debbugs.gnu.org
Subject: Re: bug#45795: 27.1; prolog-mode prolog-system switch bug
Date: Fri, 30 Jul 2021 14:39:58 +0200

k3tu0isui <at> gmail.com writes:

> I have repeatedly checked switching between GNU-Prolog and SWI-Prolog
> systems after setting `prolog-system` to buffer local values 'gnu' and
> 'swi' resp.
> Both `prolog-consult-file` and `run-prolog` are now starting the
> correct interpreter.

I don't use Prolog myself, but your patch seems to make sense to me, so
I've applied it to Emacs 28.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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