From 7132f773ba2a1dc440e39fa8ab364505f1dc61c9 Mon Sep 17 00:00:00 2001
From: Stephen A Pohl <spohl.mozilla.bugs@gmail.com>
Date: Sat, 2 Nov 2024 02:13:06 +0000
Subject: [PATCH] Bug 1833923: Start detecting when the Fn key is pressed on
 macOS, which allows for built-in macOS shortcuts (such as Fn+e for the emoji
 picker) to start working. r=masayuki

Depends on D195016

Differential Revision: https://phabricator.services.mozilla.com/D223630
---
 dom/events/KeyEventHandler.h     |  2 --
 widget/TextEvents.h              |  2 +-
 widget/cocoa/TextInputHandler.mm | 14 ++++++++++++--
 widget/cocoa/nsCocoaUtils.mm     | 18 ++++++++++++++----
 4 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/dom/events/KeyEventHandler.h b/dom/events/KeyEventHandler.h
index 5d444cf32270..974c5c4c2f64 100644
--- a/dom/events/KeyEventHandler.h
+++ b/dom/events/KeyEventHandler.h
@@ -133,13 +133,11 @@ class KeyEventHandler final {
   static const int32_t cAlt;
   static const int32_t cControl;
   static const int32_t cMeta;
-  static const int32_t cOS;
 
   static const int32_t cShiftMask;
   static const int32_t cAltMask;
   static const int32_t cControlMask;
   static const int32_t cMetaMask;
-  static const int32_t cOSMask;
 
   static const int32_t cAllModifiers;
 
diff --git a/widget/TextEvents.h b/widget/TextEvents.h
index a775dd84c41a..41bb624c9d0d 100644
--- a/widget/TextEvents.h
+++ b/widget/TextEvents.h
@@ -238,7 +238,7 @@ class WidgetKeyboardEvent final : public WidgetInputEvent {
     //       we don't have any bug reports that user cannot input proper
     //       character with Alt and/or Ctrl key.
     //       -- On macOS, IMEInputHandler::WillDispatchKeyboardEvent() clears
-    //       MODIFIER_ALT and MDOFIEIR_CONTROL of eKeyPress event only when
+    //       MODIFIER_ALT and MODIFIER_CONTROL of eKeyPress event only when
     //       TextInputHandler::InsertText() has been called for the event.
     //       I.e., they are cleared only when an editor has focus (even if IME
     //       is disabled in password field or by |ime-mode: disabled;|) because
diff --git a/widget/cocoa/TextInputHandler.mm b/widget/cocoa/TextInputHandler.mm
index e25acef5d738..a7fba34f94c0 100644
--- a/widget/cocoa/TextInputHandler.mm
+++ b/widget/cocoa/TextInputHandler.mm
@@ -545,9 +545,11 @@ bool TISInputSourceWrapper::IsDeadKey(NSEvent* aNativeKeyEvent) {
     return false;
   }
 
-  // Assmue that if control key or command key is pressed, it's not a dead key.
+  // Assume that if the control key, command key or Fn key is pressed, it's not
+  // a dead key.
   NSUInteger cocoaState = [aNativeKeyEvent modifierFlags];
-  if (cocoaState & (NSEventModifierFlagControl | NSEventModifierFlagCommand)) {
+  if (cocoaState & (NSEventModifierFlagControl | NSEventModifierFlagCommand |
+                    NSEventModifierFlagFunction)) {
     return false;
   }
 
@@ -1849,6 +1851,14 @@ bool TextInputHandler::HandleKeyDownEvent(NSEvent* aNativeEvent,
     return false;
   }
 
+  // macOS supports shortcut keys using the `Fn` key. Check first if this key
+  // event is such a shortcut key.
+  if (nsCocoaUtils::ModifiersForEvent(aNativeEvent) & MODIFIER_FN) {
+    if (mWidget->SendEventToNativeMenuSystem(aNativeEvent)) {
+      return true;
+    }
+  }
+
   // Let Cocoa interpret the key events, caching IsIMEComposing first.
   bool wasComposing = IsIMEComposing();
   bool interpretKeyEventsCalled = false;
diff --git a/widget/cocoa/nsCocoaUtils.mm b/widget/cocoa/nsCocoaUtils.mm
index 5ecca19e3b17..e0b3e1d79353 100644
--- a/widget/cocoa/nsCocoaUtils.mm
+++ b/widget/cocoa/nsCocoaUtils.mm
@@ -701,7 +701,8 @@ NSEvent* nsCocoaUtils::MakeNewCococaEventFromWidgetEvent(
       {MODIFIER_ALTGRAPH, NSEventModifierFlagOption},
       {MODIFIER_META, NSEventModifierFlagCommand},
       {MODIFIER_CAPSLOCK, NSEventModifierFlagCapsLock},
-      {MODIFIER_NUMLOCK, NSEventModifierFlagNumericPad}};
+      {MODIFIER_NUMLOCK, NSEventModifierFlagNumericPad},
+      {MODIFIER_FN, NSEventModifierFlagFunction}};
 
   NSUInteger modifierFlags = 0;
   for (uint32_t i = 0; i < std::size(sModifierFlagMap); ++i) {
@@ -786,9 +787,18 @@ Modifiers nsCocoaUtils::ModifiersForEvent(NSEvent* aNativeEvent) {
     result |= MODIFIER_NUMLOCK;
   }
 
-  // Be aware, NSEventModifierFlagFunction is included when arrow keys, home key
-  // or some other keys are pressed. We cannot check whether 'fn' key is pressed
-  // or not by the flag.
+  // Be aware, NSEventModifierFlagFunction is also set on the native event when
+  // arrow keys, the home key or some other keys are pressed. We cannot check
+  // whether the 'fn' key is pressed or not by the flag alone. We need to check
+  // that the event's keyCode falls outside the range of keys that will also set
+  // the function modifier.
+  if (!!(modifiers & NSEventModifierFlagFunction) &&
+      (aNativeEvent.type == NSKeyDown || aNativeEvent.type == NSKeyUp ||
+       aNativeEvent.type == NSFlagsChanged) &&
+      !(kVK_Return <= aNativeEvent.keyCode &&
+        aNativeEvent.keyCode <= NSModeSwitchFunctionKey)) {
+    result |= MODIFIER_FN;
+  }
 
   return result;
 }