bug#45005: 28.0.50; input method does not switch back

[Jean Louis]

* Juri Linkov <juri@linkov.net> [2020-12-08 12:10]:
> tags 45005 + patch

That is great if it is solved not to happen again.

I cannot see through. Are you sure you found the right culprit?

> > This is report for which I do not think that it is reproducible as I
> > tried to invoke it with emacs -Q and I would need to perform some work
> > from which I could not find out what invokes the bug.
> >
> > My other input method is by default set to german-postfix.
> >
> > My Emacs uptime now is about 1 day, 15 hours. About 15 hours ago, I
> > could observe that I cannot turn off the input method with C-\ but
> > that it remains engaged.
> >
> > Mode line may show DE<U: and when I press C-\ it shows U: but again I
> > can write ü ö ä and some words in other languages collide. I am using
> > other few input methods for other languages, then it becomes difficult
> > writing English as some combinations of letters get converted in other
> > letters, then I have to delete, etc. If I make new session it will of
> > course be alright. For my last 5 years I have not encountered this
> > situation that input-method kind of remains turned on even if I turn
> > it off.
> 
> This problem can happen only when the default global value of
> input-method-function is changed, so it still translates keys
> while the input method is disabled.
> 
> When an input method is activated, 'quail-activate' uses
> 
>   (setq-local input-method-function #'quail-input-method)
> 
> to set the buffer-local value, and when an input method is deactivated,
> removes the buffer-local value:
> 
>   (kill-local-variable 'input-method-function)
> 
> So it doesn't change its default global value.
> 
> The only place on the whole Emacs tree that can change the
> default global value of input-method-function is 'isearch-done':
> 
>   (if isearch-input-method-local-p
>       (setq input-method-function isearch-input-method-function)
>      (kill-local-variable 'input-method-function))
> 
> Many functions in international/isearch-x.el set isearch-input-method-local-p
> to 't', but never set it to 'nil'.  So when after using an input method
> in Isearch (enabling and disabling it) on exiting Isearch, this code
> always changes the default global value of input-method-function.
> 
> Instead of this, this code should use the same logic as used by
> 'quail-activate': when a previous input method should be re-activated,
> then set its buffer-local value, otherwise use kill-local-variable.
> 
> This logic will obsolete the variable isearch-input-method-local-p:
> 

> diff --git a/lisp/isearch.el b/lisp/isearch.el
> index a0aa250c4b..69c553deda 100644
> --- a/lisp/isearch.el
> +++ b/lisp/isearch.el
> @@ -965,10 +965,6 @@ isearch-hidden
>  ;; The value of input-method-function when isearch is invoked.
>  (defvar isearch-input-method-function nil)
>  
> -;; A flag to tell if input-method-function is locally bound when
> -;; isearch is invoked.
> -(defvar isearch-input-method-local-p nil)
> -
>  (defvar isearch--saved-overriding-local-map nil)
>  
>  ;; Minor-mode-alist changes - kind of redundant with the
> @@ -1238,7 +1234,6 @@ isearch-mode
>       search-ring-yank-pointer nil
>       isearch-opened-overlays nil
>       isearch-input-method-function input-method-function
> -     isearch-input-method-local-p (local-variable-p 'input-method-function)
>       regexp-search-ring-yank-pointer nil
>  
>       isearch-pre-scroll-point nil
> @@ -1259,8 +1254,6 @@ isearch-mode
>    ;; We must bypass input method while reading key.  When a user type
>    ;; printable character, appropriate input method is turned on in
>    ;; minibuffer to read multibyte characters.
> -  (or isearch-input-method-local-p
> -      (make-local-variable 'input-method-function))
>    (setq input-method-function nil)
>  
>    (looking-at "")
> @@ -1418,8 +1411,8 @@ isearch-done
>       (set-window-group-start (selected-window) found-start t))))
>  
>    (setq isearch-mode nil)
> -  (if isearch-input-method-local-p
> -      (setq input-method-function isearch-input-method-function)
> +  (if isearch-input-method-function
> +      (setq-local input-method-function isearch-input-method-function)
>      (kill-local-variable 'input-method-function))
>  
>    (if isearch-tool-bar-old-map
> diff --git a/lisp/international/isearch-x.el b/lisp/international/isearch-x.el
> index f50f86a035..94716721b5 100644
> --- a/lisp/international/isearch-x.el
> +++ b/lisp/international/isearch-x.el
> @@ -35,8 +35,7 @@ isearch-toggle-specified-input-method
>    (interactive)
>    (let ((overriding-terminal-local-map nil))
>      (toggle-input-method t))
> -  (setq isearch-input-method-function input-method-function
> -     isearch-input-method-local-p t)
> +  (setq isearch-input-method-function input-method-function)
>    (setq input-method-function nil)
>    (isearch-update))
>  
> @@ -46,8 +45,7 @@ isearch-toggle-input-method
>    (interactive)
>    (let ((overriding-terminal-local-map nil))
>      (toggle-input-method))
> -  (setq isearch-input-method-function input-method-function
> -     isearch-input-method-local-p t)
> +  (setq isearch-input-method-function input-method-function)
>    (setq input-method-function nil)
>    (isearch-update))
>  
> @@ -57,8 +55,7 @@ isearch-transient-input-method
>    (interactive)
>    (let ((overriding-terminal-local-map nil))
>      (activate-transient-input-method))
> -  (setq isearch-input-method-function input-method-function
> -     isearch-input-method-local-p t)
> +  (setq isearch-input-method-function input-method-function)
>    (setq input-method-function nil)
>    (isearch-update))
>  
> diff --git a/lisp/language/korea-util.el b/lisp/language/korea-util.el
> index 3821785da7..13cd6a015d 100644
> --- a/lisp/language/korea-util.el
> +++ b/lisp/language/korea-util.el
> @@ -70,8 +70,7 @@ isearch-toggle-korean-input-method
>    (interactive)
>    (let ((overriding-terminal-local-map nil))
>      (toggle-korean-input-method))
> -  (setq isearch-input-method-function input-method-function
> -     isearch-input-method-local-p t)
> +  (setq isearch-input-method-function input-method-function)
>    (setq input-method-function nil)
>    (isearch-update))
>  
> @@ -79,8 +78,7 @@ isearch-hangul-switch-symbol-ksc
>    (interactive)
>    (let ((overriding-terminal-local-map nil))
>      (quail-hangul-switch-symbol-ksc))
> -  (setq isearch-input-method-function input-method-function
> -     isearch-input-method-local-p t)
> +  (setq isearch-input-method-function input-method-function)
>    (setq input-method-function nil)
>    (isearch-update))
>  
> @@ -88,8 +86,7 @@ isearch-hangul-switch-hanja
>    (interactive)
>    (let ((overriding-terminal-local-map nil))
>      (quail-hangul-switch-hanja))
> -  (setq isearch-input-method-function input-method-function
> -     isearch-input-method-local-p t)
> +  (setq isearch-input-method-function input-method-function)
>    (setq input-method-function nil)
>    (isearch-update))
>