Make dead-key/accented-character/IME composition work — in Discord.com chat and other using Slate etc. editors

[Lampe2020]

Summary

When I try to use e.g. the backtick character in Discord in ladybird, I have to type it into the URL bar and copy it from there into the message since it's a combining symbol. Similar for ü, which on a Swedish keyboard can only be typed by typing ¨ followed by u, that then combine.
In Firefox and Vesktop, Discord manages that just fine, but in Ladybird those combining symbols simply don't appear.

Operating system

Linux

Steps to reproduce

1. Use a Swedish keyboard layout or other keyboard layout that has combining characters (i.e. that need multiple keystrokes to type)
2. Find a chat in Discord
3. Try to compose a message with e.g. ü or backticks for inline code in it.

Expected behavior

Combining characters should appear and when a compatible other character is typed after, combine with that.

Actual behavior

Combining characters don't appear, and compatible characters typed after simply appear plain if they are not combining themselves, or don't appear if they are combining as well.

URL for a reduced test case

N/A

HTML/SVG/etc. source for a reduced test case

N/A

Log output and (if possible) backtrace

N/A

Screenshots or screen recordings

Skarmsandning_20260818_010707.webm

Build flags or config settings

No response

[sideshowbarker]

Please try the patch in #11249 and see if it makes things work as expected.

[Lampe2020]

It now kinda works, but I cannot persistently type them:

Skarmsandning_20260821_153500.webm

As soon as I type anything else (space, dash, anything else) all combinational characters disappear again.
What the recording doesn't show but what I also saw now is that when I type a combinational character into the empty text field, the placeholder text does not disappear.

[sideshowbarker]

It now kinda works, but I cannot persistently type them:

OK I see now that the #11249 fix was necessary but not sufficient for making this work. Unfortunately, it seems there are at least three other major necessary things we haven’t yet implemented yet:

1. We don’t yet implement/fire composition events: No compositionstart, compositionupdate or compositionend.
2. We don’t yet implement insertCompositionText for preedit text; instead it’s justinsertText (= editors think it’s committed text).
3. We don’t fire beforeinput for IME insertions; makes the editor unable to when you’ve started dead-key/IME composing.

What’s likely happening that explains the specific behavior you’re seeing is: The Discord/Slate editor most probably keeps its own document model that it reconciles the browser DOM against. But due to the things we’re missing, we don’t actually give the editor what it expects to see in order to know to suspend its model reconciliation while you‘re composing. So it ends up re-rendering from the state of its model that never recorded the composition. And so, the composed characters you entered just get clobbered.

Update: OK yeah I see now that Slate is React-based. Should’ve known. But anyway, given that, it makes sense we break it this way.

[sideshowbarker]

I can do a PR implementing the missing stuff. But it’s a big chunk of work, so I reckon I may not have it PR-ready til mid next week or so.

[sideshowbarker]

OK, round 2: Please try the patch in #11280 and see if it gets things working as expected for you.

[Lampe2020]

I now merged the PR into my local tree with

git fetch origin pull/11280/head:deadkeyfix
git switch deadkeyfix

and triggered a build. As that will take a while and it's the middle of the night, I'll just let it run and report back after testing it tomorrow morning.

[Lampe2020]

With that PR it works :)