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

[Charalampos Mitrodimas <charmitro@posteo.net>]

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On 4/7/24 17:45, Stefan Monnier wrote:
>> +            (lambda (form) (keymap--compile-check from (and to 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))))
>> +    (when (> (length from-key) 1)
>> +      (error "FROM key %s is not a single key" from))
>> +    (when (and to (> (length to-key) 1))
>> +      (error "TO key %s is not a single key" to))
> I'd check `=` while at it (if length is 0 the error is caught by
> `aref`, but it's a less helpful error).
>
>
>          Stefan

Updated & attached.

--
Charalampos

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From 30cbe7722a677a53ae9c9f66b13153275324adc6 Mon Sep 17 00:00:00 2001
From: Charalampos Mitrodimas <charmitro@posteo.net>
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 | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/lisp/keymap.el b/lisp/keymap.el
index b2b475c7d71..51dfbf45d24 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)))
+            (lambda (form) (keymap--compile-check from (if to to nil)) 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