Codemirror + Heliboard + Firefox Mobile on Android messes up editing

[henrebotha]

Describe the issue

The Heliboard open source soft keyboard on Android uses some kind of Android text entry API that underlines words as you type (probably related to text suggestions). When using this keyboard in CM on Firefox Mobile, text insertion doesn't happen where you might expect.

1. Use Heliboard with a layout that exposes arrow keys.
2. Type the string bd sd and put the cursor to the left of bd.
3. Use the right arrow key to move the cursor to the right of bd. Note the underline under bd.
4. Type @.

You expect to have bd@ sd, but instead you get b@d sd.

Bug doesn't happen with Chrome or with Gboard or SwiftKey.

Browser and platform

Firefox Mobile 140.0.3, Heliboard 3.2

Reproduction link

No response

[marijnh]

Have you checked whether this behaves better in a raw contenteditable element?

[henrebotha]

Have you checked whether this behaves better in a raw contenteditable element?

I just did, and it's totally fine.

[marijnh]

I could not find the setting in Heliboard to get me arrow keys. Where are they?

[henrebotha]

I could not find the setting in Heliboard to get me arrow keys. Where are they?

You unfortunately have to use a custom config. I should have supplied one, sorry! Here is an export of my config which has arrow keys.

HeliBoard_backup_2025-07-07.zip

[marijnh]

I see. I'm sorry, but if the bug only occurs in a custom reconfiguration of an already non-mainstream keyboard, that seems a bit too obscure for me to work on. I found the left/right arrows in the heliboard toolbar, but those don't seem to trigger the problem.

[henrebotha]

I see. I'm sorry, but if the bug only occurs in a custom reconfiguration of an already non-mainstream keyboard, that seems a bit too obscure for me to work on. I found the left/right arrows in the heliboard toolbar, but those don't seem to trigger the problem.

Oh I totally get that. I report this not because I think it's a priority use case, but because it suggests something subtle is wrong that may have other effects. I don't expect this to be fixed immediately.

I might take a stab at it myself sometime, but I'm no Android dev.

[marijnh]

CodeMirror debugging is really just web dev, especially on Firefox (where, unlike Chrome Android, they didn't completely reinvent the text input model).