feat(webkitgtk): make input method preedit configurable

.changes/configurable-input-method-preedit.md

@@ -0,0 +1,5 @@
+---
+"wry": minor
+---
+
+On Linux, add `WebViewBuilderExtUnix::with_input_method_preedit(bool)` to make the input method preedit configurable. Defaults to `false`, preserving the behavior introduced in wry 0.29.0 (see tauri-apps/tauri#5986). Apps targeting modern webkit2gtk (≥ 2.50) can opt in to inline preedit, which CJK IMEs use to render composition state inside editable elements.

src/lib.rs

@@ -1920,6 +1920,7 @@ impl WebViewBuilderExtAndroid for WebViewBuilder<'_> {
 pub(crate) struct PlatformSpecificWebViewAttributes {
   extension_path: Option<PathBuf>,
   related_view: Option<webkit2gtk::WebView>,
+  input_method_preedit: bool,
 }
 
 #[cfg(any(
@@ -1950,6 +1951,26 @@ pub trait WebViewBuilderExtUnix<'a> {
   /// Creates a new webview sharing the same web process with the provided webview.
   /// Useful if you need to link a webview to another, for instance when using the [`WebViewBuilder::with_new_window_req_handler`].
   fn with_related_view(self, webview: webkit2gtk::WebView) -> Self;
+
+  /// Set whether the WebView's input method context should report
+  /// preedit text to the application during composition.
+  ///
+  /// When `true`, IME composition events (`compositionstart`,
+  /// `compositionupdate`, `compositionend`) fire in the DOM and
+  /// CJK input methods can render their preedit inline in editable
+  /// elements. When `false` (the default), preedit is suppressed
+  /// and the IM falls back to its own popup UI; this matches the
+  /// behavior introduced in wry 0.29.0 to mitigate
+  /// popup-positioning issues on older webkit2gtk versions (see
+  /// [tauri-apps/tauri#5986]).
+  ///
+  /// On modern webkit2gtk-4.1 (≥ 2.50) inline preedit works
+  /// correctly with major IMEs (fcitx5, ibus, etc.); apps targeting
+  /// those environments can opt in here to match the IME UX of
+  /// native GTK / Firefox / Chromium-based apps.
+  ///
+  /// [tauri-apps/tauri#5986]: https://github.com/tauri-apps/tauri/issues/5986
+  fn with_input_method_preedit(self, enabled: bool) -> Self;
 }
 
 #[cfg(any(
@@ -1979,6 +2000,11 @@ impl<'a> WebViewBuilderExtUnix<'a> for WebViewBuilder<'a> {
     self.platform_specific.related_view.replace(webview);
     self
   }
+
+  fn with_input_method_preedit(mut self, enabled: bool) -> Self {
+    self.platform_specific.input_method_preedit = enabled;
+    self
+  }
 }
 
 /// The fundamental type to present a [`WebView`].

src/webkitgtk/mod.rs

@@ -301,7 +301,7 @@ impl InnerWebView {
     }
 
     // Webview Settings
-    Self::set_webview_settings(&webview, &attributes);
+    Self::set_webview_settings(&webview, &attributes, &pl_attrs);
 
     // Webview handlers
     Self::attach_handlers(&webview, web_context, &mut attributes);
@@ -411,10 +411,19 @@ impl InnerWebView {
     builder.build()
   }
 
-  fn set_webview_settings(webview: &WebView, attributes: &WebViewAttributes) {
-    // Disable input preedit,fcitx input editor can anchor at edit cursor position
+  fn set_webview_settings(
+    webview: &WebView,
+    attributes: &WebViewAttributes,
+    pl_attrs: &super::PlatformSpecificWebViewAttributes,
+  ) {
+    // Configure input method preedit per the platform-specific
+    // attribute. Default is `false` (disabled) — fcitx-style IMEs
+    // anchor their popup at the edit cursor (see
+    // tauri-apps/tauri#5986 for the original motivation). When
+    // `true`, WebKit reports composition events to the DOM and
+    // CJK IMEs render preedit inline.
     if let Some(input_context) = webview.input_method_context() {
-      input_context.set_enable_preedit(false);
+      input_context.set_enable_preedit(pl_attrs.input_method_preedit);
     }
 
     // use system scrollbars