bug#49555: 28.0.50; height display property causes text to render with incorrect spacing

[Adam Edge <baronedge@airmail.cc>]

On 7/14/21 7:00 PM, Adam Edge wrote:
> On 7/14/21 3:55 PM, Eli Zaretskii wrote:
>>> From: Adam Edge <baronedge@airmail.cc>
>>> Date: Wed, 14 Jul 2021 01:27:22 +0300
>>>
>>> I have encountered this bug while using lsp-ui mode. When a text is
>>> propertized with the display property `height', it is then displayed
>>> with the incorrect spacing. To test it, I have used this code:
>>>
>>> (require 'lsp-ui)
>>> (let* ((text "Hello world")
>>>       (propertized (progn (add-face-text-property 0 (length text)
>>> 'lsp-ui-sideline-code-action nil text)
>>>                           text))
>>>       (overlay (make-overlay 1 1)))
>>>   (overlay-put overlay 'after-string (concat propertized
>>>                                         (propertize propertized 'display
>>> (lsp-ui-sideline--compute-height)))))
>>>
>>> lsp-ui-sideline-code-action can be any face with a font with different
>>> spacing. In my Emacs configuration, it is defined as:
>>>
>>> (font-spec :family "Fira Code" :size 14 :weight 'regular :spacing 100)
>>>
>>> When the two "Hello world"s are displayed next to each other, the one
>>> which is propertized with the "height" property displays wider. In
>>> lsp-ui's case, this causes text to be cut off by the right side of the
>>> Emacs frame as it overflows (since the code actions are displayed as an
>>> overlay on the right side of the frame).
>> I'm a bit confused by the scenario description.  Could you perhaps
>> provide a simple self-contained recipe, which would not need any
>> third-party packages like lsp-ui, and could be invoked from "emacs -Q"?
>> It sounds like any references to lsp-ui in your scenario are not
>> really relevant, and just muddy the waters?
>>
>> And what do you mean by "a font with a different spacing"? what is the
>> spacing of the default font in your case? and what is the default font
>> itself?
>>
>> Thanks.
>>
>>
>>
> Thanks for your response. I am trying to come up with something that works
> on emacs -Q. This is what I've come up with:
>
> (setq my-font (font-spec :family "Fira Code" :size 14 :weight 'regular :spacing 100))
> (set-frame-font my-font)
> (set-face-attribute 'default t :font my-font)
>
> (defface test-face '((t :inherit default))
>   "A face for testing.")
> (let* ((text "Hello world")
>        (propertized (progn (add-face-text-property 0 (length text) 'test-face nil text)
> 			   text))
>        (overlay (make-overlay 1 1)))
>   (overlay-put overlay 'after-string (concat propertized "\n"
> 					     (propertize propertized 'display '(height 1)))))
>
> Running this in the scratch buffer in emacs -Q produces two "Hello world"s,
> the latter having more space between each letter and being slightly bolder
> (which is not what I want).
>
> Another thing I've noticed is that when I just did the (set-face-attribute)
> part without (set-frame-font) and opened a new frame, the frame's font was
> the same as the one with incorrect letter spacing. When I did
> M-x describe-font RET, this is what I got in the `full name' line:Fira
> Code:pixelsize=14:foundry=CTDB:weight=normal:slant=normal:width=normal:spacing=90:scalable=true
> And the font loaded is: /usr/share/fonts/fira-code/FiraCode-Medium.ttf
> After doing the (set-frame-font), the font returned to the desired
> spacing. The `full-name' line in describe-font now is: Fira
> Code:pixelsize=14:foundry=CTDB:weight=normal:slant=normal:width=normal:spacing=100:scalable=true
> And the font loaded now is:
> /home/aedge/.local/share/fonts/FiraCode-Retina.ttf I suppose removing
> the system font should fix my problem here, and the issue can be closed,
> but why does the font change when '(height 1) is specified?
>

I am sorry, for some reason the lines in my previous email got messed up, so
I am reproducing them below;

When I did M-x describe-font RET, this is what I got in the `full name'
line:

Fira
Code:pixelsize=14:foundry=CTDB:weight=normal:slant=normal:width=normal:spacing=90:scalable=true
And the font file loaded was: /usr/share/fonts/fira-code/FiraCode-Medium.ttf

After doing the (set-frame-font), the font returned to the desired
spacing. The `full-name' line in describe-font now is:

Fira
Code:pixelsize=14:foundry=CTDB:weight=normal:slant=normal:width=normal:spacing=100:scalable=true
And the font loaded now is:
/home/aedge/.local/share/fonts/FiraCode-Retina.ttf

I suppose removing the system font should fix my problem here, and the
issue can be closed, but why does the font change when '(height 1) is
specified?