Fix Cmd key regression

Shift and Alt modifiers now register in combination with Cmd and e.g.
arrow keys.

src/MacVim/MMBackend.m

@@ -1954,8 +1954,19 @@ static void netbeansReadCallback(CFSocketRef s,
     if (mods & MOD_MASK_CMD) {
         // NOTE: For normal input (non-special, 'macmeta' off) the modifier
         // flags are already included in the key event.  However, the Cmd key
-        // flag is special and must always be added manually.  The frontend is
-        // responsible for clearing unnecessary flags when Cmd is held.
+        // flag is special and must always be added manually.
+        // The Shift flag is already included in the key when the Command
+        // key is held.  The same goes for Alt, unless Ctrl is held or
+        // 'macmeta' is set.  It is important that these flags are cleared
+        // _after_ special keys have been handled, since they should never be
+        // cleared for special keys.
+        mods &= ~MOD_MASK_SHIFT;
+        if (!(mods & MOD_MASK_CTRL)) {
+            BOOL mmta = curbuf ? curbuf->b_p_mmta : YES;
+            if (!mmta)
+                mods &= ~MOD_MASK_ALT;
+        }
+
         ASLogDebug(@"add mods=%#x", mods);
         char_u modChars[3] = { CSI, KS_MODIFIER, mods };
         add_to_input_buf(modChars, 3);

src/MacVim/MMTextViewHelper.m

@@ -162,8 +162,8 @@ KeyboardInputSourcesEqual(TISInputSourceRef a, TISInputSourceRef b)
             // HACK! When Command is held we have to more or less guess whether
             // we should use characters or charactersIgnoringModifiers.  The
             // following heuristic seems to work but it may have to change.
-            // Note that the Shift and Alt flags may be cleared before passing
-            // the event on to Vim (see doKeyDown:).
+            // Note that the Shift and Alt flags may also need to be cleared
+            // (see doKeyDown:keyCode:modifiers: in MMBackend).
             if ((flags & NSShiftKeyMask && !(flags & NSAlternateKeyMask))
                     || flags & NSControlKeyMask)
                 string = unmod;
@@ -897,18 +897,6 @@ KeyboardInputSourcesEqual(TISInputSourceRef a, TISInputSourceRef b)
     unsigned keyCode = [currentEvent keyCode];
     unsigned flags = [currentEvent modifierFlags];
 
-    if (flags & NSCommandKeyMask) {
-        // The Shift flag is already included in the key when the Command key
-        // is held.  The same goes for Alt, unless Ctrl is held or 'macmeta' is
-        // set.
-        flags &= ~NSShiftKeyMask;
-        if (!(flags & NSControlKeyMask)) {
-            id mmta = [[[self vimController] vimState] objectForKey:@"p_mmta"];
-            if (![mmta boolValue])
-                flags &= ~NSAlternateKeyMask;
-        }
-    }
-
     // The low 16 bits are not used for modifier flags by NSEvent.  Use
     // these bits for custom flags.
     flags &= NSDeviceIndependentModifierFlagsMask;