From ab4d9a9f73843486f39e8874afb303d3d5b9f0d9 Mon Sep 17 00:00:00 2001
From: Matej Knopp <matej.knopp@gmail.com>
Date: Sat, 31 Jul 2021 03:00:54 +0200
Subject: [PATCH] Do not generate keydown event for empty modifier flags
 (#27817)

* Do not generate keydown event for empty modifier flags

* Mask 0x100 bit instead of comparison

* Comment

* Update comment

* comment

* Add comment
---
 .../framework/Source/FlutterChannelKeyResponder.mm  |  8 +++++---
 .../Source/FlutterChannelKeyResponderUnittests.mm   | 13 ++++++++++++-
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponder.mm b/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponder.mm
index b6aaae1376247..29436dec17ea1 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponder.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponder.mm
@@ -39,6 +39,8 @@ - (nonnull instancetype)initWithChannel:(nonnull FlutterBasicMessageChannel*)cha
 }
 
 - (void)handleEvent:(NSEvent*)event callback:(FlutterAsyncKeyCallback)callback {
+  // Remove the modifier bits that Flutter is not interested in.
+  NSEventModifierFlags modifierFlags = event.modifierFlags & ~0x100;
   NSString* type;
   switch (event.type) {
     case NSEventTypeKeyDown:
@@ -48,9 +50,9 @@ - (void)handleEvent:(NSEvent*)event callback:(FlutterAsyncKeyCallback)callback {
       type = @"keyup";
       break;
     case NSEventTypeFlagsChanged:
-      if (event.modifierFlags < _previouslyPressedFlags) {
+      if (modifierFlags < _previouslyPressedFlags) {
         type = @"keyup";
-      } else if (event.modifierFlags > _previouslyPressedFlags) {
+      } else if (modifierFlags > _previouslyPressedFlags) {
         type = @"keydown";
       } else {
         // ignore duplicate modifiers; This can happen in situations like switching
@@ -61,7 +63,7 @@ - (void)handleEvent:(NSEvent*)event callback:(FlutterAsyncKeyCallback)callback {
     default:
       NSAssert(false, @"Unexpected key event type (got %lu).", event.type);
   }
-  _previouslyPressedFlags = event.modifierFlags;
+  _previouslyPressedFlags = modifierFlags;
   NSMutableDictionary* keyMessage = [@{
     @"keymap" : @"macos",
     @"type" : type,
diff --git a/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponderUnittests.mm b/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponderUnittests.mm
index 01254d6b7c780..d5629e900bea8 100644
--- a/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponderUnittests.mm
+++ b/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponderUnittests.mm
@@ -52,9 +52,20 @@
         callback(keyMessage);
       }));
 
-  // Key down
   FlutterChannelKeyResponder* responder =
       [[FlutterChannelKeyResponder alloc] initWithChannel:mockKeyEventChannel];
+
+  // Initial empty modifiers. This can happen when user opens window while modifier key is pressed
+  // and then releases the modifier. Shouldn't result in an event being sent.
+  // Regression test for https://github.com/flutter/flutter/issues/87339.
+  [responder handleEvent:keyEvent(NSEventTypeFlagsChanged, 0x100, @"", @"", FALSE, 60)
+                callback:^(BOOL handled) {
+                  [responses addObject:@(handled)];
+                }];
+
+  EXPECT_EQ([messages count], 0u);
+
+  // Key down
   [responder handleEvent:keyEvent(NSEventTypeKeyDown, 0x100, @"a", @"a", FALSE, 0)
                 callback:^(BOOL handled) {
                   [responses addObject:@(handled)];