Port run-prolog EMACS to SWI-Prolog 7.2.3

* lisp/progmodes/prolog.el (prolog-ensure-process):
Work around incompatibility of SWI-Prolog 7.2.3 and earlier
with the new way of dealing with the EMACS and INSIDE_EMACS
environment variables.

1 files changed, 14 insertions, 2 deletions

diff --git a/lisp/progmodes/prolog.el b/lisp/progmodes/prolog.el
index 9ee405b31e1..212a5fa69ab 100644
--- a/lisp/progmodes/prolog.el
+++ b/lisp/progmodes/prolog.el
@@ -1374,8 +1374,20 @@ the variable `prolog-prompt-regexp'."
       ()
     (with-current-buffer (get-buffer-create "*prolog*")
       (prolog-inferior-mode)
-      (apply 'make-comint-in-buffer "prolog" (current-buffer)
-             (prolog-program-name) nil (prolog-program-switches))
+
+      ;; The "INFERIOR=yes" hack is for SWI-Prolog 7.2.3 and earlier,
+      ;; which assumes it is running under Emacs if either INFERIOR=yes or
+      ;; if EMACS is set to a nonempty value.  The EMACS setting is
+      ;; obsolescent, so set INFERIOR.  Newer versions of SWI-Prolog should
+      ;; know about INSIDE_EMACS (which replaced EMACS) and should not need
+      ;; this hack.
+      (let ((process-environment
+             (if (getenv "INFERIOR")
+                 process-environment
+               (cons "INFERIOR=yes" process-environment))))
+        (apply 'make-comint-in-buffer "prolog" (current-buffer)
+               (prolog-program-name) nil (prolog-program-switches)))
+
       (unless prolog-system
         ;; Setup auto-detection.
         (setq-local