Allow keyboard and pointer grabs to hook clear_focus()

This is necessary for some grabs, which currently have no way of knowing
when the pointer/keyboard focus has left a surface. For example, without
this, a drag-and-drop grab can erroneously drop into a window that the
cursor is no longer over.

This is the plumbing needed to properly fix swaywm/sway#5220. The
existing fix, swaywm/sway#5222, relies on every grab's `enter()` hook
allowing a `NULL` surface. This is not guaranteed by the API and, in
fact, is not the case for the xdg-shell popup grab and results in a
crash when the cursor leaves a surface and does not immediately enter
another one while a popup is open (#2161).

This fix also adds an assertion to wlr_seat_pointer_notify_enter() that
ensures it's never called with a `NULL` surface. This will make Sway
crash much more until it fixes its usage of the API, so we should land
this at the same time as a fix in Sway (which I haven't posted yet).

include/wlr/types/wlr_seat.h

@@ -78,6 +78,7 @@ struct wlr_seat_pointer_grab;
 struct wlr_pointer_grab_interface {
 	void (*enter)(struct wlr_seat_pointer_grab *grab,
 			struct wlr_surface *surface, double sx, double sy);
+	void (*clear_focus)(struct wlr_seat_pointer_grab *grab);
 	void (*motion)(struct wlr_seat_pointer_grab *grab, uint32_t time_msec,
 			double sx, double sy);
 	uint32_t (*button)(struct wlr_seat_pointer_grab *grab, uint32_t time_msec,
@@ -95,6 +96,7 @@ struct wlr_keyboard_grab_interface {
 	void (*enter)(struct wlr_seat_keyboard_grab *grab,
 			struct wlr_surface *surface, uint32_t keycodes[],
 			size_t num_keycodes, struct wlr_keyboard_modifiers *modifiers);
+	void (*clear_focus)(struct wlr_seat_keyboard_grab *grab);
 	void (*key)(struct wlr_seat_keyboard_grab *grab, uint32_t time_msec,
 			uint32_t key, uint32_t state);
 	void (*modifiers)(struct wlr_seat_keyboard_grab *grab,
@@ -354,6 +356,8 @@ void wlr_seat_pointer_enter(struct wlr_seat *wlr_seat,
 
 /**
  * Clear the focused surface for the pointer and leave all entered surfaces.
+ * This function does not respect pointer grabs: you probably want
+ * `wlr_seat_pointer_notify_clear_focus()` instead.
  */
 void wlr_seat_pointer_clear_focus(struct wlr_seat *wlr_seat);
 
@@ -399,6 +403,12 @@ void wlr_seat_pointer_send_frame(struct wlr_seat *wlr_seat);
 void wlr_seat_pointer_notify_enter(struct wlr_seat *wlr_seat,
 		struct wlr_surface *surface, double sx, double sy);
 
+/**
+ * Notify the seat of a pointer leave event to the currently-focused surface.
+ * Defers to any grab of the pointer.
+ */
+void wlr_seat_pointer_notify_clear_focus(struct wlr_seat *wlr_seat);
+
 /**
  * Notify the seat of motion over the given surface. Pass surface-local
  * coordinates where the pointer motion occurred. Defers to any grab of the
@@ -485,6 +495,8 @@ void wlr_seat_keyboard_enter(struct wlr_seat *seat,
 
 /**
  * Clear the focused surface for the keyboard and leave all entered surfaces.
+ * This function does not respect keyboard grabs: you probably want
+ * `wlr_seat_keyboard_notify_clear_focus()` instead.
  */
 void wlr_seat_keyboard_clear_focus(struct wlr_seat *wlr_seat);
 
@@ -511,6 +523,12 @@ void wlr_seat_keyboard_notify_enter(struct wlr_seat *seat,
 		struct wlr_surface *surface, uint32_t keycodes[], size_t num_keycodes,
 		struct wlr_keyboard_modifiers *modifiers);
 
+/**
+ * Notify the seat of a keyboard leave event to the currently-focused surface.
+ * Defers to any keyboard grabs.
+ */
+void wlr_seat_keyboard_notify_clear_focus(struct wlr_seat *wlr_seat);
+
 /**
  * Start a grab of the keyboard of this seat. The grabber is responsible for
  * handling all keyboard events until the grab ends.

types/data_device/wlr_drag.c

@@ -159,6 +159,11 @@ static void drag_handle_pointer_enter(struct wlr_seat_pointer_grab *grab,
 	drag_set_focus(drag, surface, sx, sy);
 }
 
+static void drag_handle_pointer_clear_focus(struct wlr_seat_pointer_grab *grab) {
+	struct wlr_drag *drag = grab->data;
+	drag_set_focus(drag, NULL, 0, 0);
+}
+
 static void drag_handle_pointer_motion(struct wlr_seat_pointer_grab *grab,
 		uint32_t time, double sx, double sy) {
 	struct wlr_drag *drag = grab->data;
@@ -238,6 +243,7 @@ static void drag_handle_pointer_cancel(struct wlr_seat_pointer_grab *grab) {
 static const struct wlr_pointer_grab_interface
 		data_device_pointer_drag_interface = {
 	.enter = drag_handle_pointer_enter,
+	.clear_focus = drag_handle_pointer_clear_focus,
 	.motion = drag_handle_pointer_motion,
 	.button = drag_handle_pointer_button,
 	.axis = drag_handle_pointer_axis,
@@ -303,6 +309,10 @@ static void drag_handle_keyboard_enter(struct wlr_seat_keyboard_grab *grab,
 	// nothing has keyboard focus during drags
 }
 
+static void drag_handle_keyboard_clear_focus(struct wlr_seat_keyboard_grab *grab) {
+	// nothing has keyboard focus during drags
+}
+
 static void drag_handle_keyboard_key(struct wlr_seat_keyboard_grab *grab,
 		uint32_t time, uint32_t key, uint32_t state) {
 	// no keyboard input during drags
@@ -323,6 +333,7 @@ static void drag_handle_keyboard_cancel(struct wlr_seat_keyboard_grab *grab) {
 static const struct wlr_keyboard_grab_interface
 		data_device_keyboard_drag_interface = {
 	.enter = drag_handle_keyboard_enter,
+	.clear_focus = drag_handle_keyboard_clear_focus,
 	.key = drag_handle_keyboard_key,
 	.modifiers = drag_handle_keyboard_modifiers,
 	.cancel = drag_handle_keyboard_cancel,

types/seat/wlr_seat_keyboard.c

@@ -21,6 +21,10 @@ static void default_keyboard_enter(struct wlr_seat_keyboard_grab *grab,
 	wlr_seat_keyboard_enter(grab->seat, surface, keycodes, num_keycodes, modifiers);
 }
 
+static void default_keyboard_clear_focus(struct wlr_seat_keyboard_grab *grab) {
+	wlr_seat_keyboard_clear_focus(grab->seat);
+}
+
 static void default_keyboard_key(struct wlr_seat_keyboard_grab *grab,
 		uint32_t time, uint32_t key, uint32_t state) {
 	wlr_seat_keyboard_send_key(grab->seat, time, key, state);
@@ -37,6 +41,7 @@ static void default_keyboard_cancel(struct wlr_seat_keyboard_grab *grab) {
 
 const struct wlr_keyboard_grab_interface default_keyboard_grab_impl = {
 	.enter = default_keyboard_enter,
+	.clear_focus = default_keyboard_clear_focus,
 	.key = default_keyboard_key,
 	.modifiers = default_keyboard_modifiers,
 	.cancel = default_keyboard_cancel,
@@ -311,15 +316,22 @@ void wlr_seat_keyboard_enter(struct wlr_seat *seat,
 void wlr_seat_keyboard_notify_enter(struct wlr_seat *seat,
 		struct wlr_surface *surface, uint32_t keycodes[], size_t num_keycodes,
 		struct wlr_keyboard_modifiers *modifiers) {
+	// NULL surfaces are prohibited in the grab-compatible API. Use
+	// wlr_seat_keyboard_notify_clear_focus() instead.
+	assert(surface);
 	struct wlr_seat_keyboard_grab *grab = seat->keyboard_state.grab;
 	grab->interface->enter(grab, surface, keycodes, num_keycodes, modifiers);
 }
 
 void wlr_seat_keyboard_clear_focus(struct wlr_seat *seat) {
-	// TODO respect grabs here?
 	wlr_seat_keyboard_enter(seat, NULL, NULL, 0, NULL);
 }
 
+void wlr_seat_keyboard_notify_clear_focus(struct wlr_seat *seat) {
+	struct wlr_seat_keyboard_grab *grab = seat->keyboard_state.grab;
+	grab->interface->clear_focus(grab);
+}
+
 bool wlr_seat_keyboard_has_grab(struct wlr_seat *seat) {
 	return seat->keyboard_state.grab->interface != &default_keyboard_grab_impl;
 }

types/seat/wlr_seat_pointer.c

@@ -15,6 +15,10 @@ static void default_pointer_enter(struct wlr_seat_pointer_grab *grab,
 	wlr_seat_pointer_enter(grab->seat, surface, sx, sy);
 }
 
+static void default_pointer_clear_focus(struct wlr_seat_pointer_grab *grab) {
+	wlr_seat_pointer_clear_focus(grab->seat);
+}
+
 static void default_pointer_motion(struct wlr_seat_pointer_grab *grab,
 		uint32_t time, double sx, double sy) {
 	wlr_seat_pointer_send_motion(grab->seat, time, sx, sy);
@@ -42,6 +46,7 @@ static void default_pointer_cancel(struct wlr_seat_pointer_grab *grab) {
 
 const struct wlr_pointer_grab_interface default_pointer_grab_impl = {
 	.enter = default_pointer_enter,
+	.clear_focus = default_pointer_clear_focus,
 	.motion = default_pointer_motion,
 	.button = default_pointer_button,
 	.axis = default_pointer_axis,
@@ -331,10 +336,18 @@ void wlr_seat_pointer_end_grab(struct wlr_seat *wlr_seat) {
 
 void wlr_seat_pointer_notify_enter(struct wlr_seat *wlr_seat,
 		struct wlr_surface *surface, double sx, double sy) {
+	// NULL surfaces are prohibited in the grab-compatible API. Use
+	// wlr_seat_pointer_notify_clear_focus() instead.
+	assert(surface);
 	struct wlr_seat_pointer_grab *grab = wlr_seat->pointer_state.grab;
 	grab->interface->enter(grab, surface, sx, sy);
 }
 
+void wlr_seat_pointer_notify_clear_focus(struct wlr_seat *wlr_seat) {
+	struct wlr_seat_pointer_grab *grab = wlr_seat->pointer_state.grab;
+	grab->interface->clear_focus(grab);
+}
+
 void wlr_seat_pointer_notify_motion(struct wlr_seat *wlr_seat, uint32_t time,
 		double sx, double sy) {
 	clock_gettime(CLOCK_MONOTONIC, &wlr_seat->last_event);

types/xdg_shell/wlr_xdg_popup.c

@@ -25,6 +25,10 @@ static void xdg_pointer_grab_enter(struct wlr_seat_pointer_grab *grab,
 	}
 }
 
+static void xdg_pointer_grab_clear_focus(struct wlr_seat_pointer_grab *grab) {
+	wlr_seat_pointer_clear_focus(grab->seat);
+}
+
 static void xdg_pointer_grab_motion(struct wlr_seat_pointer_grab *grab,
 		uint32_t time, double sx, double sy) {
 	wlr_seat_pointer_send_motion(grab->seat, time, sx, sy);
@@ -59,6 +63,7 @@ static void xdg_pointer_grab_cancel(struct wlr_seat_pointer_grab *grab) {
 
 static const struct wlr_pointer_grab_interface xdg_pointer_grab_impl = {
 	.enter = xdg_pointer_grab_enter,
+	.clear_focus = xdg_pointer_grab_clear_focus,
 	.motion = xdg_pointer_grab_motion,
 	.button = xdg_pointer_grab_button,
 	.cancel = xdg_pointer_grab_cancel,
@@ -72,6 +77,10 @@ static void xdg_keyboard_grab_enter(struct wlr_seat_keyboard_grab *grab,
 	// keyboard focus should remain on the popup
 }
 
+static void xdg_keyboard_grab_clear_focus(struct wlr_seat_keyboard_grab *grab) {
+	// keyboard focus should remain on the popup
+}
+
 static void xdg_keyboard_grab_key(struct wlr_seat_keyboard_grab *grab, uint32_t time,
 		uint32_t key, uint32_t state) {
 	wlr_seat_keyboard_send_key(grab->seat, time, key, state);
@@ -88,6 +97,7 @@ static void xdg_keyboard_grab_cancel(struct wlr_seat_keyboard_grab *grab) {
 
 static const struct wlr_keyboard_grab_interface xdg_keyboard_grab_impl = {
 	.enter = xdg_keyboard_grab_enter,
+	.clear_focus = xdg_keyboard_grab_clear_focus,
 	.key = xdg_keyboard_grab_key,
 	.modifiers = xdg_keyboard_grab_modifiers,
 	.cancel = xdg_keyboard_grab_cancel,

types/xdg_shell_v6/wlr_xdg_popup_v6.c

@@ -35,6 +35,10 @@ static void xdg_pointer_grab_enter(struct wlr_seat_pointer_grab *grab,
 	}
 }
 
+static void xdg_pointer_grab_clear_focus(struct wlr_seat_pointer_grab *grab) {
+	wlr_seat_pointer_clear_focus(grab->seat);
+}
+
 static void xdg_pointer_grab_motion(struct wlr_seat_pointer_grab *grab,
 		uint32_t time, double sx, double sy) {
 	wlr_seat_pointer_send_motion(grab->seat, time, sx, sy);
@@ -69,6 +73,7 @@ static void xdg_pointer_grab_cancel(struct wlr_seat_pointer_grab *grab) {
 
 static const struct wlr_pointer_grab_interface xdg_pointer_grab_impl = {
 	.enter = xdg_pointer_grab_enter,
+	.clear_focus = xdg_pointer_grab_clear_focus,
 	.motion = xdg_pointer_grab_motion,
 	.button = xdg_pointer_grab_button,
 	.cancel = xdg_pointer_grab_cancel,
@@ -82,6 +87,10 @@ static void xdg_keyboard_grab_enter(struct wlr_seat_keyboard_grab *grab,
 	// keyboard focus should remain on the popup
 }
 
+static void xdg_keyboard_grab_clear_focus(struct wlr_seat_keyboard_grab *grab) {
+	// keyboard focus should remain on the popup
+}
+
 static void xdg_keyboard_grab_key(struct wlr_seat_keyboard_grab *grab,
 		uint32_t time, uint32_t key, uint32_t state) {
 	wlr_seat_keyboard_send_key(grab->seat, time, key, state);
@@ -98,6 +107,7 @@ static void xdg_keyboard_grab_cancel(struct wlr_seat_keyboard_grab *grab) {
 
 static const struct wlr_keyboard_grab_interface xdg_keyboard_grab_impl = {
 	.enter = xdg_keyboard_grab_enter,
+	.clear_focus = xdg_keyboard_grab_clear_focus,
 	.key = xdg_keyboard_grab_key,
 	.modifiers = xdg_keyboard_grab_modifiers,
 	.cancel = xdg_keyboard_grab_cancel,