A new approach to handling flagsChanged with IME

Bypass cocoa's flagsChanged handling and call handleevent ourselves,
this allows us to know exactly what the IME is doing. Hopefully fixes
issues with IMEs that change state on modifier key presses.

Fixes #4541

glfw/cocoa_init.m

@@ -800,12 +800,26 @@ int _glfwPlatformInit(void)
         return nil;
     };
 
+    NSEvent* (^flags_changed_block)(NSEvent*) = ^ NSEvent* (NSEvent* event)
+    {
+        debug_key("-------------- flags changed -----------------\n");
+        debug_key("%s\n", [[event description] UTF8String]);
+        last_keydown_shortcut_event.virtual_key_code = 0xffff;
+        NSWindow *kw = [NSApp keyWindow];
+        if (kw && kw.contentView) [kw.contentView flagsChanged:event];
+        else debug_key("flagsChanged ignored as no keyWindow present\n");
+        return nil;
+    };
+
     _glfw.ns.keyUpMonitor =
         [NSEvent addLocalMonitorForEventsMatchingMask:NSEventMaskKeyUp
                                               handler:keyup_block];
     _glfw.ns.keyDownMonitor =
         [NSEvent addLocalMonitorForEventsMatchingMask:NSEventMaskKeyDown
                                               handler:keydown_block];
+    _glfw.ns.flagsChangedMonitor =
+        [NSEvent addLocalMonitorForEventsMatchingMask:NSEventMaskFlagsChanged
+                                              handler:flags_changed_block];
 
     if (_glfw.hints.init.ns.chdir)
         changeToResourcesDirectory();
@@ -890,6 +904,8 @@ void _glfwPlatformTerminate(void)
         [NSEvent removeMonitor:_glfw.ns.keyUpMonitor];
     if (_glfw.ns.keyDownMonitor)
         [NSEvent removeMonitor:_glfw.ns.keyDownMonitor];
+    if (_glfw.ns.flagsChangedMonitor)
+        [NSEvent removeMonitor:_glfw.ns.flagsChangedMonitor];
 
     if (_glfw.ns.appleSettings != nil) {
         [_glfw.ns.appleSettings release];

glfw/cocoa_platform.h

@@ -174,8 +174,7 @@ typedef struct _GLFWlibraryNS
     IOHIDManagerRef     hidManager;
     id                  unicodeData;
     id                  helper;
-    id                  keyUpMonitor;
+    id                  keyUpMonitor, keyDownMonitor, flagsChangedMonitor;
-    id                  keyDownMonitor;
     id                  appleSettings;
     id                  nibObjects;
 

glfw/cocoa_window.m

@@ -752,7 +752,6 @@ static const NSRange kEmptyRange = { NSNotFound, 0 };
     NSMutableAttributedString* markedText;
     NSRect markedRect;
     bool marked_text_cleared_by_insert;
-    bool in_key_down;
     NSString *input_source_at_last_key_event;
 }
 
@@ -1151,14 +1150,12 @@ is_ascii_control_char(char x) {
         debug_key("\x1b[31mPress:\x1b[m native_key: 0x%x (%s) glfw_key: 0x%x %schar_count: %lu deadKeyState: %u repeat: %d ",
                 keycode, safe_name_for_keycode(keycode), key, format_mods(mods), char_count, window->ns.deadKeyState, event.ARepeat);
         marked_text_cleared_by_insert = false;
-        in_key_down = true;
         if (process_text) {
             // this will call insertText which will fill up _glfw.ns.text
             [self interpretKeyEvents:@[event]];
         } else {
             window->ns.deadKeyState = 0;
         }
-        in_key_down = false;
         if (window->ns.deadKeyState && (char_count == 0 || keycode == 0x75)) {
             // 0x75 is the delete key which needs to be ignored during a compose sequence
             debug_key("Sending pre-edit text for dead key (text: %s markedText: %s).\n", format_text(_glfw.ns.text), glfw_keyevent.text);
@@ -1201,16 +1198,19 @@ is_ascii_control_char(char x) {
         // insertText followed by setMarkedText
         UPDATE_PRE_EDIT_TEXT;
     }
-#undef CLEAR_PRE_EDIT_TEXT
-#undef UPDATE_PRE_EDIT_TEXT
 }
 
 - (void)flagsChanged:(NSEvent *)event
 {
     int action = GLFW_RELEASE;
-    const unsigned int modifierFlags =
+    const char old_first_char = _glfw.ns.text[0];
-        [event modifierFlags] & NSEventModifierFlagDeviceIndependentFlagsMask;
+    _glfw.ns.text[0] = 0;
+    const NSUInteger modifierFlags = [event modifierFlags] & NSEventModifierFlagDeviceIndependentFlagsMask;
     const uint32_t key = vk_code_to_functional_key_code([event keyCode]);
+    const unsigned int keycode = [event keyCode];
+    const int mods = translateFlags(modifierFlags);
+    const bool process_text = !_glfw.ignoreOSKeyboardProcessing && (!window->ns.textInputFilterCallback || window->ns.textInputFilterCallback(key, mods, keycode, modifierFlags) != 1);
+
     switch(key) {
         case GLFW_FKEY_CAPS_LOCK:
             action = modifierFlags & NSEventModifierFlagCapsLock ? GLFW_PRESS : GLFW_RELEASE; break;
@@ -1229,7 +1229,17 @@ is_ascii_control_char(char x) {
         default:
             return;
     }
-    GLFWkeyevent glfw_keyevent = {.key = key, .native_key = [event keyCode], .native_key_id = [event keyCode], .action = action, .mods = translateFlags(modifierFlags)};
+    GLFWkeyevent glfw_keyevent = {.key = key, .native_key = keycode, .native_key_id = keycode, .action = action, .mods = mods};
+    marked_text_cleared_by_insert = false;
+    NSTextInputContext *inpctx = [NSTextInputContext currentInputContext];
+    if (process_text && inpctx) {
+        // this will call insertText which will fill up _glfw.ns.text
+        [inpctx handleEvent:event];
+        if (marked_text_cleared_by_insert) { CLEAR_PRE_EDIT_TEXT; }
+        if (_glfw.ns.text[0]) glfw_keyevent.text = _glfw.ns.text;
+        else _glfw.ns.text[0] = old_first_char;
+    }
+    glfw_keyevent.ime_state = GLFW_IME_NONE;
     _glfwInputKeyboard(window, &glfw_keyevent);
 }
 
@@ -1246,6 +1256,9 @@ is_ascii_control_char(char x) {
     _glfwInputKeyboard(window, &glfw_keyevent);
 }
 
+#undef CLEAR_PRE_EDIT_TEXT
+#undef UPDATE_PRE_EDIT_TEXT
+
 - (void)scrollWheel:(NSEvent *)event
 {
     double deltaX = [event scrollingDeltaX];
@@ -1423,11 +1436,6 @@ void _glfwPlatformUpdateIMEState(_GLFWwindow *w, const GLFWIMEUpdateEvent *ev) {
     char *s = _glfw.ns.text + strnlen(_glfw.ns.text, sizeof(_glfw.ns.text));
     snprintf(s, sizeof(_glfw.ns.text) - (s - _glfw.ns.text), "%s", utf8);
     _glfw.ns.text[sizeof(_glfw.ns.text) - 1] = 0;
-    if (!in_key_down && !strlen(utf8)) {
-        // is called by cocoa when a modifier is pressed, for example shift
-        GLFWkeyevent dummy = {.action = GLFW_RELEASE, .ime_state = GLFW_IME_PREEDIT_CHANGED};
-        _glfwInputKeyboard(window, &dummy);
-    }
 }
 
 - (void)doCommandBySelector:(SEL)selector