Define and use new procedure display-symbol-keys-p

* lisp/frame.el (display-symbol-keys-p): Define.

* lisp/simple.el (normal-erase-is-backspace-setup-frame): Use eq
instead of memq.
(normal-erase-is-backspace-mode): Use display-symbol-keys-p.

2 files changed, 14 insertions, 3 deletions

diff --git a/lisp/frame.el b/lisp/frame.el
index cc8ca49b3b7..aa14e87d7b8 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -1927,6 +1927,16 @@ frame's display)."
      (t
       nil))))
 
+(defun display-symbol-keys-p (&optional display)
+  "Return non-nil if DISPLAY supports symbol names as keys.
+This means that, for example, DISPLAY can differentiate between
+the keybinding RET and [return]."
+  (let ((frame-type (framep-on-display display)))
+    (or (memq frame-type '(x w32 ns pc))
+        ;; MS-DOS and MS-Windows terminals have built-in support for
+        ;; function (symbol) keys
+        (memq system-type '(ms-dos windows-nt)))))
+
 (declare-function x-display-screens "xfns.c" (&optional terminal))
 
 (defun display-screens (&optional display)
diff --git a/lisp/simple.el b/lisp/simple.el
index 306df967661..857e0fc001b 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -8690,7 +8690,7 @@ call `normal-erase-is-backspace-mode' (which see) instead."
                (and (not noninteractive)
                     (or (memq system-type '(ms-dos windows-nt))
                         (memq window-system '(w32 ns))
-                        (and (memq window-system '(x))
+                        (and (eq window-system 'x)
                              (fboundp 'x-backspace-delete-keys-p)
                              (x-backspace-delete-keys-p))
                         ;; If the terminal Emacs is running on has erase char
@@ -8701,6 +8701,8 @@ call `normal-erase-is-backspace-mode' (which see) instead."
              normal-erase-is-backspace)
            1 0)))))
 
+(declare-function display-symbol-keys-p "frame" (&optional display))
+
 (define-minor-mode normal-erase-is-backspace-mode
   "Toggle the Erase and Delete mode of the Backspace and Delete keys.
 
@@ -8736,8 +8738,7 @@ See also `normal-erase-is-backspace'."
   (let ((enabled (eq 1 (terminal-parameter
                         nil 'normal-erase-is-backspace))))
 
-    (cond ((or (memq window-system '(x w32 ns pc))
-               (memq system-type '(ms-dos windows-nt)))
+    (cond ((display-symbol-keys-p)
            (let ((bindings
                   '(([M-delete] [M-backspace])
                     ([C-M-delete] [C-M-backspace])