feat(webkitgtk): make input method preedit configurable

[eldenpark]

Background

I ran into this while experimenting with a Linux desktop app on wry 0.53.5 against webkit2gtk-4.1 2.50.x on Ubuntu 24.04, and trying to use a plain <input> for Korean text. With a default wry build, typing Hangul felt broken — each keystroke either dropped the in-progress composition or briefly flickered into a detached fcitx popup that didn't track the cursor.

The root cause is that wry currently disables IME preedit unconditionally on Linux, so there is no way for any wry-based app to display preedit text inline. webkitgtk::InnerWebView::set_webview_settings calls set_enable_preedit(false) with no opt-out, which means CJK users never see what they're composing inside <input> / <textarea> / contenteditable elements — they only see characters appear after the IME commits, with no underlined preedit in between.

That call landed in wry 0.29.0 to work around fcitx popup positioning on older webkit2gtk (tauri-apps/tauri#5986). On modern webkit2gtk-4.1 (≥ 2.50) the popup positioning issue is gone, but the unconditional false is now actively preventing the standard IME UX that GTK, Firefox, and Chromium-based apps all render correctly on the same systems.

What this PR does

Adds WebViewBuilderExtUnix::with_input_method_preedit(bool) so apps can opt in to inline preedit:

let builder = WebViewBuilder::new()
    .with_input_method_preedit(true);

The default stays false, so this is non-breaking — existing apps that rely on the popup behavior keep getting it.

When enabled, webkit's GtkIMContext reports compositionstart / compositionupdate / compositionend to the DOM, and the IME renders its preedit string (with the standard underline) inline at the cursor.

Testing

Manually tested on Ubuntu 24.04 (X11) + webkit2gtk-4.1 2.50.x with two IMEs:

• fcitx5-hangul (Korean): typing 안녕 shows inline preedit underlined at the cursor; commit lands cleanly; repeated send-and-clear works in a loop.
• fcitx5-anthy (Japanese): typing romaji like nihongo shows にほんご inline; Space opens the candidate window; Enter commits.

I haven't tested Wayland or ibus — happy to add those data points if a maintainer wants them before merging.

Related

• [bug] IME window is not positioning correctly on tauri tauri#5986 — original report behind unconditional set_enable_preedit(false)
• [bug] IME window position appears out of input/textarea (cannot inline-input) on Tauri v2 apps in Linux tauri#11412 — recent user request for inline preedit
• [bug] Input Method does not work properly tauri#8264 — related IME report
• fix(linux):fix fcitx input method wrong positioning #955 — earlier discussion

[eldenpark]

Hi maintainers, would love a review when you have time. Happy to take it in a different direction if there's a better approach.

[FabianLars]

since the other pr, wry's minimum webkitgtk increased and distros removed old-ish versions from their repos so i wonder if it's fine to enable for all again? Though that indeed would require more testing, so at least wayland and ideally also older webkitgtk/gtk versions and perhaps in a tiling wm as well since it was first reported there 🤔

[eldenpark]

@FabianLars I'm leaning toward enabling it for everyone too, but I unfortunately couldn't test on Wayland. I did do my testing under i3, so that covers the tiling-WM + X11 at least.

Is there anyone on Wayland who could give it a spin before we flip the default?

[FabianLars]

I have wayland kde and wayland gnome to test but i never used IMEs so idk how to set that up and use it 🙃

I asked on our discord server, hopefully someone's up to the task there :)

[github-actions]

Package Changes Through cac61a5

There are 1 changes which include wry with minor

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
wry	0.55.1	0.56.0

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