IME: don't forward key-release without correspinding key-press

After commit e2189903 in wlroots, when ctrl-f is pressed in firefox with
a IME client running, the following key-release event for "f" is not
sent, thus "f" is repeated like "ffffffffff..." in the input box of
firefox. This is because the key-release event for "f" is firstly
forwarded to the IME client and then sent via the virtual keyboard created
by the IME client while the preceding key-press event is sent via physical
keyboard, and with e2189903, key-release events without a corresponding
key-press event on the same keyboard is not emitted to the compositor.

So this commit fixes this problem by not forwarding the key-release event
to the IME client unless the corresponding key-press event was also
forwarded.

src/core/seat/input-method-relay.cpp

@@ -284,6 +284,19 @@ bool wf::input_method_relay::handle_key(struct wlr_keyboard *kbd, uint32_t time,
         return false;
     }
 
+    if (state == WL_KEYBOARD_KEY_STATE_PRESSED) {
+        pressed_keys.insert(key);
+    } else
+    {
+        // Don't forward the release event if the press event for the same key
+        // has also been forwarded.
+        if (!pressed_keys.count(key))
+        {
+            return false;
+        }
+        pressed_keys.erase(key);
+    }
+
     wlr_input_method_keyboard_grab_v2_set_keyboard(keyboard_grab, kbd);
     wlr_input_method_keyboard_grab_v2_send_key(keyboard_grab, time, key, state);
     return true;

src/core/seat/input-method-relay.hpp

@@ -7,6 +7,7 @@
 
 #include <vector>
 #include <memory>
+#include <set>
 
 namespace wf
 {
@@ -25,6 +26,8 @@ class input_method_relay : public text_input_v3_im_relay_interface_t
     uint32_t next_done_serial = 0;
     void send_im_done();
 
+    std::multiset<uint32_t> pressed_keys;
+
     text_input *find_focusable_text_input();
     void set_focus(wlr_surface*);