Ivy will trigger insert-char error: C-x 8 RET c will input ^F instead of ^L.

[hongyi-zhao]

On Ubuntu 20.04, I'm using git master version of Emacs and swiper with the following configuration:

 (straight-use-package
 `(swiper :type git :host github :repo "abo-abo/swiper"
    :pre-build (
               ;("bash" "-c" "cd ~/.emacs.d/straight/repos/swiper")
               ;https://github.com/abo-abo/swiper/issues/2886#issuecomment-860605327
               ("make" "deps")
               ("make" "compile")
               )))
                    
(require 'ivy)
(ivy-mode 1)
(setq ivy-use-virtual-buffers t)
(setq ivy-count-format "(%d/%d) ")

I found the above configuration will trigger the insert-char error: C-x 8 RET c will input ^F instead of ^L, see the screenshot below for more detailed info:

If I don't use the above configuration, the result will look like follows:

It's well known that the second should be the expected character input by the corresponding typesetting sequence.

Any hints for this problem will be highly appreciated.

Regards,
HY

[basil-conto]

I don't think there's anything Ivy can do about this, i.e. as far as I'm concerned it's a pilot error arising from a known limitation of eager interactive completion systems like that of Ivy.

C-x 8 RET (insert-char) reads user input using the function read-char-by-name, which unconditionally calls completing-read.

In vanilla Emacs, no completion actually takes place until the user asks for it by typing e.g. TAB. So read-char-by-name actually behaves differently depending on whether you perform completion: you can enter either a hex codepoint like c (ASCII ^L), or the equivalent Unicode name FORM FEED (FF).

With Ivy, the completion happens straight away, so typing c just filters the set of Unicode names to those containing the character c. The first such result just happens to be ACKNOWLEDE (ASCII ^F).

So the solution is to exit completion without selecting the current candidate, i.e. type C-M-j (ivy-immediate-done) instead of RET (ivy-done). See (info "(ivy) Key bindings for single selection action then exit minibuffer").

[hongyi-zhao]

Got it. Thank you very much for your insightful analysis.

[basil-conto]

You're welcome, glad it helped.

By the way: if you have counsel installed you can also use the command counsel-unicode-char as an alternative or in addition to insert-char. It wouldn't really help in your ^L scenario, but it has the benefit of including the codepoint, Unicode name, and a character preview all in one.

By the way part two: a faster way of inserting ^L is C-q C-l (C-q causes any subsequent character sequence to be inserted literally).

[hongyi-zhao]

Thank you very much for your additional comments.

Out of curiosity, I tried this configuration, and it gives the following fancy representations when I hit C-x 8 RET:

Any comments/hints/suggestions with this style?

Regards,
HY

[basil-conto]

Any comments/hints/suggestions with this style?

Not sure what you're looking for - AFAICT that config uses Vertico, Consult, Marginalia, and Selectrum instead of Ivy and Counsel. I suggest you go with whichever set of packages works best for you.

[hongyi-zhao]

Thank you again for your advice.

[hongyi-zhao]

By the way: if you have counsel installed you can also use the command counsel-unicode-char as an alternative or in addition to insert-char.

Thanks. I adopted the key binding suggested here:

("C-x 8 RET" . counsel-unicode-char)