API Review: Custom context menu Spellcheck

specs/CustomContextMenuSpellcheck.md

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+Spell Check Support for Custom Context Menus
+===
+
+# Background
+
+When a host application renders a custom context menu via the `ContextMenuRequested` event, spell check
+suggestions for misspelled words are not available. The browser's built-in spell check pipeline resolves
+suggestions asynchronously, but there is no mechanism for custom context menu hosts to retrieve or apply
+these suggestions.
+
+This feature adds spell check support to custom context menus by extending
+`ICoreWebView2ContextMenuTarget` with a new `ICoreWebView2ContextMenuTarget2` interface. The host
+checks whether a misspelled word is present, then asynchronously retrieves spelling suggestions.
+
+# Description
+
+The `ICoreWebView2ContextMenuTarget` is extended with `ICoreWebView2ContextMenuTarget2`.
+This new interface provides:
+
+- **`HasSpellingError`** — Read-only BOOL property indicating whether the context menu target
+  contains a spelling error. This is always available synchronously when the event fires.
+- **`GetSpellCheckSuggestions(handler)`** — Asynchronously retrieves spell check suggestions as
+  `ICoreWebView2ContextMenuItem` objects. Each suggestion has a `Label` (display text) and
+  `CommandId` (opaque identifier).
+
+**Runtime version detection:** If `QueryInterface` (QI) for `Target2` returns `E_NOINTERFACE`, the host
+is running on an older runtime that does not support this feature.
+
+**Why async?** Spell check suggestions are resolved asynchronously by the platform spell checker
+(e.g., Windows `ISpellChecker`). When `ContextMenuRequested` fires, suggestions may not yet be
+available. `GetSpellCheckSuggestions` handles this transparently — it invokes the handler
+immediately if suggestions are ready, or waits for the platform spell checker to deliver them.
+If the platform spell checker does not respond within an internal timeout, the handler is invoked
+with an empty collection.
+
+**Commanding model:** The host applies a suggestion by passing its `CommandId` to
+`put_SelectedCommandId` on the EventArgs — the same execution path used for Cut, Copy, Paste, and
+all other context menu items. No separate execution method is needed.
+
+# Examples
+
+## Win32 C++
+
+```cpp
+webView->add_ContextMenuRequested(
+    Callback<ICoreWebView2ContextMenuRequestedEventHandler>(
+        [this](ICoreWebView2* sender,
+               ICoreWebView2ContextMenuRequestedEventArgs* args) -> HRESULT
+        {
+            wil::com_ptr<ICoreWebView2ContextMenuTarget> target;
+            CHECK_FAILURE(args->get_ContextMenuTarget(&target));
+
+            // QI for Target2 — returns E_NOINTERFACE on older runtimes.
+            auto target2 = wil::try_com_query<
+                ICoreWebView2ContextMenuTarget2>(target);
+            if (!target2)
+                return S_OK;
+
+            // Check if the context menu target has a spelling error.
+            BOOL hasSpellingError = FALSE;
+            CHECK_FAILURE(target2->get_HasSpellingError(&hasSpellingError));
+            if (!hasSpellingError)
+                return S_OK;
+
+            // Take deferral — menu will be shown after async callback.
+            wil::com_ptr<ICoreWebView2Deferral> deferral;
+            CHECK_FAILURE(args->GetDeferral(&deferral));
+            CHECK_FAILURE(args->put_Handled(true));
+
+            // Asynchronously retrieve spell check suggestions.
+            CHECK_FAILURE(target2->GetSpellCheckSuggestions(
+                Callback<
+                    ICoreWebView2GetSpellCheckSuggestionsCompletedHandler>(
+                    [args, deferral](
+                        HRESULT errorCode,
+                        ICoreWebView2ContextMenuItemCollection*
+                            suggestions) -> HRESULT
+                    {
+                        // Enumerate suggestions — each has Label and CommandId.
+                        UINT32 count = 0;
+                        if (SUCCEEDED(errorCode) && suggestions)
+                            suggestions->get_Count(&count);
+
+                        for (UINT32 i = 0; i < count; i++)
+                        {
+                            wil::com_ptr<ICoreWebView2ContextMenuItem> item;
+                            suggestions->GetValueAtIndex(i, &item);
+                            wil::unique_cotaskmem_string label;
+                            item->get_Label(&label);
+                            INT32 cmdId;
+                            item->get_CommandId(&cmdId);
+                            // ... add to custom menu using label and cmdId ...
+                        }
+
+                        // Apply selection via unified commanding.
+                        // args->put_SelectedCommandId(selectedCmdId);
+
+                        deferral->Complete();
+                        return S_OK;
+                    })
+                    .Get()));
+            return S_OK;
+        })
+        .Get(),
+    &m_contextMenuRequestedToken);
+```
+
+## .NET/WinRT
+
+```csharp
+webView.CoreWebView2.ContextMenuRequested += async (sender, args) =>
+{
+    var target = args.ContextMenuTarget;
+
+    // Check if the context menu target has a spelling error.
+    if (!target.HasSpellingError)
+        return;
+
+    // Take deferral — menu will be shown after async call completes.
+    var deferral = args.GetDeferral();
+    args.Handled = true;
+
+    // Asynchronously retrieve spell check suggestions.
+    IReadOnlyList<CoreWebView2ContextMenuItem> suggestions =
+        await target.GetSpellCheckSuggestionsAsync();
+
+    // Build custom menu with suggestions.
+    var contextMenu = new ContextMenuStrip();
+    foreach (var suggestion in suggestions)
+    {
+        var item = new ToolStripMenuItem(suggestion.Label);
+        var capturedId = suggestion.CommandId;
+        item.Click += (_, _) =>
+        {
+            // Apply selection via unified commanding.
+            args.SelectedCommandId = capturedId;
+        };
+        contextMenu.Items.Add(item);
+    }
+
+    // Show menu and complete deferral when closed.
+    contextMenu.Closed += (_, _) => deferral.Complete();
+    contextMenu.Show(webView, new Point(args.Location.X, args.Location.Y));
+};
+```
+
+# API Details
+
+## Win32 COM IDL
+
+```idl
+// ─── ContextMenuTarget2: Spell check support ───
+
+/// Extends `ICoreWebView2ContextMenuTarget` with spell check support for
+/// custom context menus.
+///
+/// The host can `QueryInterface` the `ICoreWebView2ContextMenuTarget` returned
+/// by `ICoreWebView2ContextMenuRequestedEventArgs::get_ContextMenuTarget` to
+/// obtain this interface. Check `HasSpellingError` to determine whether
+/// the context menu was invoked on a misspelled word, then call
+/// `GetSpellCheckSuggestions` to asynchronously retrieve spelling corrections.
+///
+/// To apply a suggestion, pass the selected item's `CommandId` to
+/// `ICoreWebView2ContextMenuRequestedEventArgs::put_SelectedCommandId`.
+[uuid(f7a3b8c1-2d4e-5f6a-8b9c-0d1e2f3a4b5c), object, pointer_default(unique)]
+interface ICoreWebView2ContextMenuTarget2 : ICoreWebView2ContextMenuTarget {
+  /// Returns TRUE if the context menu target contains a spelling error.
+  /// When TRUE, call `GetSpellCheckSuggestions` to retrieve the available
+  /// spelling correction suggestions asynchronously.
+  [propget] HRESULT HasSpellingError([out, retval] BOOL* value);
+
+  /// Asynchronously retrieves spell check suggestion options as a collection
+  /// of context menu items. The handler is invoked immediately if suggestions
+  /// are already available, or when they become available from the platform
+  /// spell check engine. Each item's `Label` is the suggestion text and its
+  /// `CommandId` can be passed to `put_SelectedCommandId` to apply the
+  /// correction. The handler receives an empty collection if no suggestions
+  /// are available, if `HasSpellingError` is FALSE, or if the underlying
+  /// spell check service does not respond within an internal timeout.
+  /// Multiple concurrent calls are supported; each handler will be invoked
+  /// with the same result when suggestions become available.
+  /// Returns `E_POINTER` if `handler` is null.
+  HRESULT GetSpellCheckSuggestions(
+      [in] ICoreWebView2GetSpellCheckSuggestionsCompletedHandler* handler);
+}
+
+/// Receives the result of the `GetSpellCheckSuggestions` method.
+[uuid(d73832f9-d05b-438d-bb6d-6441245221e3), object, pointer_default(unique)]
+interface ICoreWebView2GetSpellCheckSuggestionsCompletedHandler : IUnknown {
+  /// Provides the result of the corresponding asynchronous method.
+  /// Each item in the `suggestions` collection is an
+  /// `ICoreWebView2ContextMenuItem` whose `Label` is the suggestion text
+  /// and whose `CommandId` uniquely identifies it. To apply a suggestion,
+  /// pass the selected item's `CommandId` to
+  /// `ICoreWebView2ContextMenuRequestedEventArgs.put_SelectedCommandId`.
+  HRESULT Invoke(
+      [in] HRESULT errorCode,
+      [in] ICoreWebView2ContextMenuItemCollection* suggestions);
+}
+```
+
+## .NET/WinRT
+
+```csharp
+namespace Microsoft.Web.WebView2.Core
+{
+    runtimeclass CoreWebView2ContextMenuTarget
+    {
+        // Existing members unchanged.
+
+        [interface_name("ICoreWebView2ContextMenuTarget2")]
+        {
+            /// <summary>
+            /// Returns TRUE if the context menu target contains a spelling error.
+            /// </summary>
+            Boolean HasSpellingError { get; };
+
+            /// <summary>
+            /// Asynchronously retrieves spell check suggestions. Each item's
+            /// CommandId can be passed to SelectedCommandId to apply the correction.
+            /// </summary>
+            Windows.Foundation.IAsyncOperation<IVectorView<CoreWebView2ContextMenuItem>>
+                GetSpellCheckSuggestionsAsync();
+        }
+    }
+}
+```
+
+# Behavioral Details
+
+## Discovery Flow
+
+| Step | Action | Result |
+|------|--------|--------|
+| 1 | QI for `Target2` from `ContextMenuTarget` | `E_NOINTERFACE` → old runtime, fall back to default menu |
+| 2 | Read `HasSpellingError` | `TRUE` → spelling error present; `FALSE` → no spelling error |
+| 3 | Call `GetSpellCheckSuggestions(handler)` | Handler invoked when suggestions are available |
+
+## Suggestion Item Properties
+
+Each `ICoreWebView2ContextMenuItem` returned by `GetSpellCheckSuggestions` has:
+
+| Property | Value |
+|----------|-------|
+| `Label` | Suggestion text (e.g., "the") |
+| `CommandId` | WebView2-allocated opaque ID (e.g., 50001) |
+| `Name` | `"spellCheckSuggestion"` |
+| `Kind` | `COREWEBVIEW2_CONTEXT_MENU_ITEM_KIND_COMMAND` |
+| `IsEnabled` | true |
+| `IsChecked` | false |
+| `Icon` | null |
+| `ShortcutKeyDescription` | empty string |
+| `Children` | null |
+
+## Async Timing
+
+Spell check suggestions are resolved asynchronously by the platform spell checker in the browser
+process. When `ContextMenuRequested` fires, the suggestions may be:
+
+| State | Meaning | `GetSpellCheckSuggestions` behavior |
+|-------|---------|-------------------------------------|
+| **Ready** | Suggestions already resolved before the event fired | Handler invoked immediately |
+| **Not Ready** | Platform spell checker still working | Handler stored; invoked when browser delivers results via IPC, or after internal timeout with empty collection |
+
+The host does **not** need to check readiness — `GetSpellCheckSuggestions` handles both cases
+transparently. In the typical case, the platform spell checker responds within a few milliseconds.
+The internal timeout is a conservative safeguard for rare scenarios where the platform spell checker
+is slow or unresponsive.
+
+### Host Patterns
+
+**Pattern 1: Wait-then-show** (simpler — used in the examples above)
+
+The host defers the context menu, calls `GetSpellCheckSuggestions`, and builds/shows the menu
+only after the handler fires. This produces a complete menu in one shot but delays appearance
+if suggestions are not yet ready.
+
+```
+ContextMenuRequested → put_Handled(TRUE) + GetDeferral → GetSpellCheckSuggestions
+    → [handler fires] → build & show menu → complete deferral
+```
+
+**Pattern 2: Show-then-update** (responsive — mirrors browser built-in behavior)
+
+The host shows the context menu immediately with a placeholder (e.g., "Loading suggestions…")
+and updates it in-place when the handler fires. This keeps menu appearance instant at the cost
+of added complexity. Since the host owns the custom context menu UI, it can modify the menu
+while it is open.
+
+```
+ContextMenuRequested → put_Handled(TRUE) + GetDeferral → show menu with placeholder
+    → GetSpellCheckSuggestions → [handler fires] → update menu items in-place
+    → [user selects] → complete deferral
+```
+
+Either pattern is valid. Pattern 1 is recommended for most hosts because the delay is typically
+imperceptible (suggestions often resolve before the event fires or within a few milliseconds
+after). Pattern 2 is appropriate for hosts that require guaranteed instant menu appearance.
+
+# Appendix
+
+## Planned Spell Check Extensions
+
+The following actions will be added as additional `ICoreWebView2ContextMenuItem` entries in the
+collection returned by `GetSpellCheckSuggestions`. No new interfaces or methods are required:
+
+| Action | `Name` value |
+|--------|-------------|
+| Add to Dictionary | `"spellCheckAddToDictionary"` |
+| Ignore (session) | `"spellCheckIgnore"` |
+
+These follow the same commanding model: the host renders them like any other item and applies via
+`SelectedCommandId`. A `Language` property (BCP-47 tag of the dictionary that flagged the misspelling)
+may also be added to `ICoreWebView2ContextMenuTarget2` in a follow-up version. Profile-level
+spell check configuration (`IsSpellCheckEnabled`, `SpellCheckLanguages`) is tracked as a separate
+follow-up.
+
+## Relationship to Existing APIs
+
+| Existing API | This Feature |
+|-------------|-------------|
+| `EventArgs.MenuItems` | Synchronous snapshot of menu items |
+| `EventArgs.SelectedCommandId` | Execution path — now also used for spell check suggestions |
+| `ContextMenuItem.CommandId` | Already used for all items — spell check items join this pool |
+| `ContextMenuItem.Label` | Display text — spell check suggestions use this for the suggestion word |
+| `EventArgs.GetDeferral()` | Must be held across the async `GetSpellCheckSuggestions` gap |
+| `ContextMenuTarget` | Base target — QI to `Target2` for spell check support |