fix(wasm): Keep the TextBox in sync with Android soft keyboard input - #24502

Fixes Android soft-keyboard IME synchronization for Skia WebAssembly TextBoxes.

Changes:

• Synchronizes hidden-input text, caret, and composition state.
• Adds composition start-index reporting and key-name fallback mapping.
• Adds runtime coverage for composition ordering and Backspace behavior.

Suppressed comments (5)

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/Devices/Input/BrowserKeyboardInputSource.cs:55

• The new FromKey fallback is not exercised by the added soft-keyboard tests: those events are stopped at the hidden input before the document-level BrowserKeyboardInputSource callback runs. Add a direct OnNativeKeyboardEvent regression case such as code="", key="Backspace" and assert VirtualKey.Back; otherwise this mapping can regress without a test.

		var virtualKey = BrowserVirtualKeyHelper.FromCode(code);
		if (virtualKey is VirtualKey.None)
		{
			// Soft keyboards report an empty code, so the key name is all there is to go on.
			virtualKey = BrowserVirtualKeyHelper.FromKey(key);
		}

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:167

• Unlike OnCompositionUpdated, syncTextFromInput does not honor core.IsReadOnly; ProcessTextInput accepts the value. Because the hidden element is never marked read-only, a focused read-only TextBox can be mutated by a composing soft-keyboard input that this new unconditional sync forwards. Reject native input for read-only cores (or configure the hidden input accordingly) before syncing it.

					BrowserInvisibleTextBoxViewExtension.syncTextFromInput(input);

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:167

• This raises TextCompositionChanged before syncTextFromInput updates the managed TextBox. On the first preedit, handlers can therefore observe a composition range that is outside Text (the existing IME sample reads that range from Text), and the event ordering differs from the normal IME path, which applies text before raising the event. Update the managed value first while preserving the platform-apply guard, then raise the composition event.

						BrowserInvisibleTextBoxViewExtension._imeExports.OnCompositionUpdated(
							BrowserInvisibleTextBoxViewExtension.compositionText,
							BrowserInvisibleTextBoxViewExtension.findCompositionStart(input));
					}
					BrowserInvisibleTextBoxViewExtension.syncTextFromInput(input);

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:216

• With Safari's ordering, the committed input event arrives after compositionend. Clearing isComposing and completing here means the later oninput skips findCompositionStart; when an IME has reopened over existing text, the managed session still has the caret captured at compositionstart, so TextCompositionEndedEventArgs.StartIndex reports the wrong range. Defer completion until the following input, or otherwise carry that input's computed range into completion.

				BrowserInvisibleTextBoxViewExtension.isComposing = false;
				if (ev.data.length > 0) {
					BrowserInvisibleTextBoxViewExtension._imeExports.OnCompositionCompleted(ev.data);

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_TextBox.BrowserSoftKeyboard.cs:58

• This test does not actually model the Safari ordering described in its comment: ComposePreedit already dispatches an input event before compositionend, so ab has been synced before completion and the post-end input is only a duplicate. It therefore cannot catch a completion callback observing stale managed text; construct the sequence with the first committed input after compositionend and assert the composition event state as well as the final value.

		ComposePreedit("ab", "ab", caret: 2);
		DispatchComposition("compositionend", "ab");
		DispatchInput("insertCompositionText", "ab", isComposing: false);
		SetHiddenInputValue("ab ", caret: 3);
		DispatchInput("insertText", " ", isComposing: false);

• Files reviewed: 6/6 changed files
• Comments generated: 2
• Review effort level: Lite

Suppressed comments (5)

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/Devices/Input/BrowserKeyboardInputSource.cs:55

• The new FromKey fallback is not exercised by the added soft-keyboard tests: those dispatch events on the hidden input, where the TypeScript handler stops propagation before OnNativeKeyboardEvent is called. The existing browser keyboard tests cover only non-empty event.code, so a regression in mapping an empty-code Backspace/Enter to its key name would pass; add a direct OnNativeKeyboardEvent test for the fallback.

		var virtualKey = BrowserVirtualKeyHelper.FromCode(code);
		if (virtualKey is VirtualKey.None)
		{
			// Soft keyboards report an empty code, so the key name is all there is to go on.
			virtualKey = BrowserVirtualKeyHelper.FromKey(key);
		}

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/UI/Xaml/Controls/TextBox/WasmImeTextBoxExtension.cs:71

• In Safari's ordering, compositionend arrives before the committed input event. This raises TextCompositionEnded with TextAlreadyApplied before the hidden input's value has been synchronized, so managed handlers observe the old Text (the IME sample computes the committed substring from that property); only the later input event fixes the final value. Defer completion/ended notification until after the trailing input sync, or synchronize managed text before raising these events.

		Instance._isComposing = false;
		Instance.CompositionCompleted?.Invoke(Instance, new ImeCompositionEventArgs(text, textAlreadyApplied: true));
		Instance.CompositionEnded?.Invoke(Instance, EventArgs.Empty);

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:481

• This guard suppresses every setText call during an input callback, including the writeback from TextBoxView.UpdateTextFromNative when BeforeTextChanging or text coercion changes/rejects the DOM value. In that case the hidden input keeps the rejected value while managed Text has another value; composition completion is marked already applied, so no later path necessarily resynchronizes them. Suppress only the exact echo, or restore the managed value and end the composition when the input was rejected.

				if (BrowserInvisibleTextBoxViewExtension.isComposing && BrowserInvisibleTextBoxViewExtension.isSyncingFromInput) {
					return;

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:216

• Safari can deliver the committed input event after compositionend, but this invokes OnCompositionCompleted immediately and marks the managed composition complete before that input syncs TextBox.Text. TextCompositionEnded handlers therefore see stale text and a range that may not exist; the existing IME sample's substring lookup will report the committed preedit as out of range in this ordering. Buffer the completion notification until the value has been synchronized, or otherwise apply the committed value before raising the managed event.

				BrowserInvisibleTextBoxViewExtension.isComposing = false;
				if (ev.data.length > 0) {
					BrowserInvisibleTextBoxViewExtension._imeExports.OnCompositionCompleted(ev.data);

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_TextBox.BrowserSoftKeyboard.cs:58

• This test does not actually replay the Safari ordering described in its comment: ComposePreedit dispatches the final input before compositionend, and the post-end input carries the same already-synchronized value. Consequently it cannot catch handlers observing stale TextCompositionEnded state in Safari order. Model the final preedit with compositionupdate only, then set the value and dispatch the committed input after compositionend.

		// Safari order: the input event carrying the committed preedit follows compositionend.
		DispatchComposition("compositionstart", "");
		ComposePreedit("ab", "ab", caret: 2);
		DispatchComposition("compositionend", "ab");
		DispatchInput("insertCompositionText", "ab", isComposing: false);
		SetHiddenInputValue("ab ", caret: 3);
		DispatchInput("insertText", " ", isComposing: false);

• Files reviewed: 6/6 changed files
• Comments generated: 1
• Review effort level: Lite

Suppressed comments (1)

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:50

• The described key-name fallback is not implemented here: for an empty or unmapped event.code, this branch only stops propagation, while BrowserKeyboardInputSource.OnNativeKeyboardEvent still calls BrowserVirtualKeyHelper.FromCode(code) and never uses KeyboardEvent.key. Consequently such events still become VirtualKey.None wherever they are routed to managed input; add that fallback in the keyboard source or remove the claim from the PR description.

		private static isSoftKeyboardKey(ev: KeyboardEvent): boolean {
			return ev.keyCode === BrowserInvisibleTextBoxViewExtension.ANDROID_IME_KEYCODE || ev.code === "";
		}

• Files reviewed: 7/7 changed files
• Comments generated: 1
• Review effort level: Lite

Suppressed comments (4)

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:50

• This only recognizes an empty code (or keyCode 229) as a soft-keyboard event. The document path still maps only FromCode(code); for a key such as { key: 'Backspace', code: 'Unidentified' }, this predicate is false, the handler's later preventDefault() runs, and managed code receives VirtualKey.None, so deletion still fails. Add the key-name fallback or classify these unmapped events as native before they are prevented.

		private static isSoftKeyboardKey(ev: KeyboardEvent): boolean {
			return ev.keyCode === BrowserInvisibleTextBoxViewExtension.ANDROID_IME_KEYCODE || ev.code === "";
		}

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:69

• The active-element check still admits only HTMLInputElement, while createInput creates an HTMLTextAreaElement for multiline (acceptsReturn) TextBoxes. Native selection changes in those controls therefore never reach OnSelectionChanged, leaving the managed caret stale when the IME or native keyboard moves it during composition. Include HTMLTextAreaElement in this guard.

						if (input.selectionDirection == "backward") {
							BrowserInvisibleTextBoxViewExtension._exports.OnSelectionChanged(input.selectionEnd, input.selectionStart - input.selectionEnd);
						} else {
							BrowserInvisibleTextBoxViewExtension._exports.OnSelectionChanged(input.selectionStart, input.selectionEnd - input.selectionStart);

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:267

• An empty compositionupdate is valid when an IME clears or cancels its preedit, but value.startsWith("", editEnd) is always true here. This returns the end of the value (or the suffix boundary) instead of the caret captured at compositionstart, so the managed StartIndex and ended range can jump to the end of existing text. Preserve the composition-start caret for the empty-preedit case before using the diff.

			// The preedit ends where the edited region ends, or starts where it starts.
			const editEnd = value.length - suffix;
			if (editEnd >= text.length && value.startsWith(text, editEnd - text.length)) {
				return editEnd - text.length;

src/Uno.UI/UI/Xaml/Controls/TextBoxCore/TextBoxCore.IME.cs:156

• syncFromInput invokes OnCompositionUpdated before syncing the input value into managed text. For an empty preedit, IsCompositionTextApplied("") is always true because the zero-length comparison succeeds, so this branch raises TextCompositionChanged while Text still has the old value during delete/cancel updates. Keep that update pending until the input value has been applied, then flush it after the sync so handlers never observe a stale composition range.

		if (textAlreadyApplied && !IsCompositionTextApplied(compositionText))
		{
			_compositionChangedPending = true;
		}
		else
		{
			_host.RaiseTextCompositionChanged(new TextCompositionChangedEventArgs(_compositionStartIndex, _compositionLength));

• Files reviewed: 7/7 changed files
• Comments generated: 0 new
• Review effort level: Lite

Suppressed comments (1)

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:50

• The PR description says unmapped event.code values fall back to the key name, but this change only classifies empty/Unidentified codes as native soft-keyboard input. The keyboard bridge still passes non-empty codes directly to BrowserVirtualKeyHelper.FromCode, whose unknown-code path returns VirtualKey.None, so that promised fallback is not implemented for other unmapped codes. Please add the fallback in the bridge (with coverage) or remove that claim from the PR description.

		private static isSoftKeyboardKey(ev: KeyboardEvent): boolean {
			return ev.keyCode === BrowserInvisibleTextBoxViewExtension.ANDROID_IME_KEYCODE || ev.code === "" || ev.code === "Unidentified";
		}

• Files reviewed: 7/7 changed files
• Comments generated: 2
• Review effort level: Lite

Suppressed comments (1)

src/Uno.UI.Runtime.Skia.WebAssembly.Browser/ts/Runtime/BrowserInvisibleTextBoxViewExtension.ts:161

• The hidden <textarea> normalizes CR/CRLF to LF, but this records the pre-normalized managed string. On a multiline TextBox, compositionend therefore sees a phantom value change even before the user edits anything. Initialize the synchronization marker from the actual DOM value.

			BrowserInvisibleTextBoxViewExtension.lastSyncedValue = text;

• Files reviewed: 7/7 changed files
• Comments generated: 1
• Review effort level: Lite

• Files reviewed: 7/7 changed files
• Comments generated: 0 new
• Review effort level: Lite