Subject: bug#70139: [PATCH] Improve key-translate to support removing translations

From: Charalampos Mitrodimas <[email-masked]>
Date: Tue, 9 Apr 2024 13:07:50 +0000

On 4/9/24 15:57, Stefan Monnier via Bug reports for GNU Emacs, the Swiss 
army knife of text editors wrote:
>> -            (lambda (form) (keymap--compile-check from to) form)))
>> +            (lambda (form) (keymap--compile-check from (if to to nil)) form)))
>                                                            ^^^^^^^^^^^^^^
>
> ??
>
> Just like (and to to), this is just a complicated way to say `to`.
> What is the underlying idea?

I was trying to pass nil to keymap--compile-check but I was complicating 
this for no reason. Reverted it completely, apologies.
From 2c39b3ac7ddffa600ec2982db76162e1456df19f Mon Sep 17 00:00:00 2001
From: Charalampos Mitrodimas <[email-masked]>
Date: Tue, 2 Apr 2024 19:02:46 +0000
Subject: [PATCH] Improve key-translate to support removing translations

This patch enhances the key-translate function to allow removing
keyboard translations by passing nil as the second argument (TO).

If TO is nil, any existing translation for the FROM key will be removed.
The compiler macro is updated to only check TO when it is non-nil.

This change makes key-translate more consistent with the behavior of
keyboard-translate, providing a way to remove translations without
having to specify the same key for both FROM and TO.

The documentation string is updated to reflect the new behavior.

* lisp/keymap.el (key-translate): support removing translations by
  passing nil as the second argument (TO). Also throw error if multiple
  items passed. (Bug#70139)
---
 lisp/keymap.el | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/lisp/keymap.el b/lisp/keymap.el
index b2b475c7d71..2fae7754bb0 100644
--- a/lisp/keymap.el
+++ b/lisp/keymap.el
@@ -379,20 +379,35 @@ key-valid-p
 
 (defun key-translate (from to)
   "Translate character FROM to TO on the current terminal.
+
 This function creates a `keyboard-translate-table' if necessary
 and then modifies one entry in it.
 
-Both FROM and TO should be specified by strings that satisfy `key-valid-p'."
+Both FROM and TO should be specified by strings that satisfy `key-valid-p'.
+If TO is nil, remove any existing translation for FROM."
   (declare (compiler-macro
             (lambda (form) (keymap--compile-check from to) form)))
   (keymap--check from)
-  (keymap--check to)
-  (or (char-table-p keyboard-translate-table)
-      (setq keyboard-translate-table
-            (make-char-table 'keyboard-translate-table nil)))
-  (aset keyboard-translate-table
-        (aref (key-parse from) 0)
-        (aref (key-parse to) 0)))
+  (when to
+    (keymap--check to))
+  (let ((from-key (key-parse from))
+        (to-key (and to (key-parse to))))
+    (cond
+     ((= (length from-key) 0)
+      (error "FROM key is empty"))
+     ((> (length from-key) 1)
+      (error "FROM key %s is not a single key" from)))
+    (cond
+     ((and to (= (length to-key) 0))
+      (error "TO key is empty"))
+     ((and to (> (length to-key) 1))
+      (error "TO key %s is not a single key" to)))
+    (or (char-table-p keyboard-translate-table)
+        (setq keyboard-translate-table
+              (make-char-table 'keyboard-translate-table nil)))
+    (aset keyboard-translate-table
+          (aref from-key 0)
+          (and to (aref to-key 0)))))
 
 (defun keymap-lookup (keymap key &optional accept-default no-remap position)
   "Return the binding for command KEY in KEYMAP.
-- 
2.39.2