1762819 - {inc} CSS letter-spacing with display:inline causing unexpected space when scaling or modifying CSS in Firefox

Status: NEW

(Core :: Layout: Text and Fonts, defect)

Description

[aldwis]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:98.0) Gecko/20100101 Firefox/98.0

Steps to reproduce:

HTML:
<pre>11556650
44332210
55443320
55443320
11556650
44332210</pre>

CSS:
pre{
background: red;
letter-spacing: 1em;
display: inline;}

Tested on CodePen.io
run the code, and:
zoom with the browser zoom function
or try to modify CSS in the Inspector

Actual results:

on any zoom, a space added to the end of every line of the <pre>

Comment 1

[aldwis]

https://jsfiddle.net/qdbr9e14/

Comment 2

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Layout' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 3

[Daniel Holbert [:dholbert]]

Attachment: testcase 1

Here's the testcase, with a button added to make and remove a temporary style change (adjusting width on the pre element). This is sufficient to cause the unexpected layout-change noted in the bug report.

STR:

1. Load this testcase.
2. Click the button.

EXPECTED RESULTS:
No change; each line should still be the same length, just as in the initial rendering of the page.

ACTUAL RESULTS:
The first and second line (i.e. all but the last line) get a bit longer, as shown by the background-color.

Comment 4

[Daniel Holbert [:dholbert]]

Note: in older Firefox builds (e.g. Nightly 2015-01-01), the initial rendering matches what I describe in ACTUAL RESULTS; and clicking the button doesn't have any effect.

Comment 5

[Daniel Holbert [:dholbert]]

(In reply to Daniel Holbert [:dholbert] from comment #4)

Note: in older Firefox builds (e.g. Nightly 2015-01-01), the initial rendering matches what I describe in ACTUAL RESULTS; and clicking the button doesn't have any effect.

Looks like we switched from this to our current "unstable" behavior in bug 1643126.

(Pushlog for the behavior-change is https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=63dc5e9b1b02b0aebd6badfe5eaef7bb9aa8f430&tochange=7f7b983390650cbc7d736e92fd3e1f629a30ac02 in which this looks like the most-likely candidate.)

So, the fact that our behavior here is "unstable" (unexpectedly changing on relayout/zoom) is a regression from bug 1643126. Marking as-such.

Comment 6

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1643126

Comment 7

[BugBot [:suhaib / :marco/ :calixte]]

:jfkthame, since you are the author of the regressor, bug 1643126, could you take a look?
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