bug#38485: Customizing glyph widths

[Clément Pit-Claudel]

On 2019-12-04 13:45, Eli Zaretskii wrote:
>> Cc: casouri@gmail.com, 38485@debbugs.gnu.org
>> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
>> Date: Wed, 4 Dec 2019 13:14:19 -0500
>>
>>>> I'm thinking something like `:display-width 3' or maybe `display-width 
>>>> "~~>"' (the former would mean "as wide as three spaces in the default 
>>>> font"; the later, "as wide as `~~>' in the default font").
>>>> These properties would be applied by prettify-symbols-mode in addition to 
>>>> composition.
>>>
>>> I don't understand why would prettify-symbols-mode want to do this via
>>> a text property, instead of via a buffer-local variable.
>>
>> Would this buffer-local variable be an alist mapping each character to the 
>> desired width?
> 
> No, it will simply make each prettified symbol take up the same width
> as the original characters of the symbol that were composed.  Isn't
> that what everyone would want, and want for _all_ prettified symbols?

Another example: the nameless-mode pacakge uses prettification to display the 
name of the current file as :, so that in foo-bar.el the symbol foo-bar-xyz 
displays as :xyz (with a different color for the colon) to shorten lines and 
improve readability.  Widening this ':' would defeat the purpose of that 
package.

Clément.