GNU bug report logs - #60094
current-column returns an incorrect number of columns for some characters

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Rodrigo Morales <moralesrodrigo1100 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: current-column returns an incorrect number of columns for some
 characters
Date: Thu, 15 Dec 2022 11:40:55 -0500

[Message part 1 (text/plain, inline)]

TL; DR: `current-column' returns `2' when the cursor is in the first
column and the line contains a single emoji or a Chinese character. The
expected value is `1' as happens when the line contains `a' or even the
highest defined codepoint in Unicode: `U+10FFFD'.

In the minimal working example below, you can see that `current-columns'
returns `1' when the line contains the character `a' and the cursor is
located after it.

,----
| cat ~/e/main.el
`----

,----
| (with-temp-buffer
|   (insert "a")
|   (end-of-line)
|   (princ (current-column)))
`----

,----
| emacs -Q --batch -l ~/e/main.el
`----

,----
| 1
`----

In the minimal working example below, you can see that `current-columns'
returns `1' when the line contains the character `􏿽' (highest defined
codepoint in Unicode, U+10FFFD) and the cursor is located after it.

,----
| cat ~/e/main.el
`----

,----
| (with-temp-buffer
|   (insert "􏿽")
|   (end-of-line)
|   (princ (current-column)))
`----

,----
| emacs -Q --batch -l ~/e/main.el
`----

,----
| 1
`----

In the minimal working example below, you can see that `current-columns'
returns `2' when the line contains an emoji and the cursor is located
after it.

,----
| cat ~/e/main.el
`----

,----
| (with-temp-buffer
|   (insert "👋")
|   (end-of-line)
|   (princ (current-column)))
`----

,----
| emacs -Q --batch -l ~/e/main.el
`----

,----
| 2
`----

In the minimal working example below, you can see that `current-columns'
returns `2' when the line contains a Chinese character and the cursor is
located after it.

,----
| cat ~/e/main.el
`----

,----
| (with-temp-buffer
|   (insert "你")
|   (end-of-line)
|   (princ (current-column)))
`----

,----
| emacs -Q --batch -l ~/e/main.el
`----

,----
| 2
`----

[Message part 2 (text/html, inline)]

Message #8 received at 60094 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Rodrigo Morales <moralesrodrigo1100 <at> gmail.com>
Cc: 60094 <at> debbugs.gnu.org
Subject: Re: bug#60094: current-column returns an incorrect number of columns
 for some characters
Date: Thu, 15 Dec 2022 18:56:43 +0200

tags 60094 notabug
thanks

> From: Rodrigo Morales <moralesrodrigo1100 <at> gmail.com>
> Date: Thu, 15 Dec 2022 11:40:55 -0500
> 
> In the minimal working example below, you can see that `current-columns'
> returns `2' when the line contains an emoji and the cursor is located
> after it.
> 
> ,----
> | cat ~/e/main.el
> `----
> 
> ,----
> | (with-temp-buffer
> |   (insert "👋")
> |   (end-of-line)
> |   (princ (current-column)))
> `----
> 
> ,----
> | emacs -Q --batch -l ~/e/main.el
> `----
> 
> ,----
> | 2
> `----
> 
> In the minimal working example below, you can see that `current-columns'
> returns `2' when the line contains a Chinese character and the cursor is
> located after it.
> 
> ,----
> | cat ~/e/main.el
> `----
> 
> ,----
> | (with-temp-buffer
> |   (insert "你")
> |   (end-of-line)
> |   (princ (current-column)))
> `----
> 
> ,----
> | emacs -Q --batch -l ~/e/main.el
> `----
> 
> ,----
> | 2
> `----

These are the expected and correct results: these characters have
width that is very close to 2 canonical columns.  And current-column
counts canonical columns, not just characters.

If you type regular characters, like 'a', above or below this Emoji or
the Chinese character, you will see that for each such Emoji you can
type 2 regular characters.

So there's no bug here: Emacs does what it's supposed to do.  The doc
string of current-column says:

  This is calculated by adding together the widths of all the displayed
  representations of the character between the start of the previous line
  and point (e.g., control characters will have a width of 2 or 4, tabs
  will have a variable width).

Note the "displayed representations" part.

Message #15 received at 60094-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 60094-done <at> debbugs.gnu.org, Rodrigo Morales <moralesrodrigo1100 <at> gmail.com>
Subject: Re: bug#60094: current-column returns an incorrect number of columns
 for some characters
Date: Mon, 4 Sep 2023 14:11:42 -0700

Eli Zaretskii <eliz <at> gnu.org> writes:

> tags 60094 notabug
> thanks
[...]
> So there's no bug here: Emacs does what it's supposed to do.  The doc
> string of current-column says:
>
>   This is calculated by adding together the widths of all the displayed
>   representations of the character between the start of the previous line
>   and point (e.g., control characters will have a width of 2 or 4, tabs
>   will have a variable width).
>
> Note the "displayed representations" part.

Thanks, I'm therefore closing this bug report.

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