view: try to reduce confusion in focused_view tracking

Our current approach to handling the focused/active view is a bit
confusing. In particular, it's hard to be sure when server->focused_view
is or isn't in sync with the real wlroots keyboard focus.

Try to clean things up a bit. In particular:

- Add comments to server->focused_view and desktop_focused_view() to
  clarify that they should match, but it's not guaranteed.

- desktop_focused_view() now prints a warning if it detects that
  server->focused_view is out of sync. We should keep an eye out for
  this warning, and if we see it, try to figure out why it happened.

- For consistency, use only "focus/defocus" as the verbs in function
  names rather than "activate". This is a bit arbitrary, but the idea is
  that focus is the primary action while the active/inactive state is a
  side effect.

- view_focus/defocus() replace view_set_activated() and now update both
  focus and active/inactive state, to try to keep them in sync.

- Add comments at view_focus/defocus() to warn against calling them
  directly (we should generally call the desktop.c functions).

- desktop_focus_view(NULL) is now forbidden and is no longer handled as
  a special case to clear the focus. This was (at least to me) a
  surprising behavior and caused trouble when working on another change.

- To maintain existing behavior, desktop_focus_topmost_mapped_view() now
  explicitly clears the focus if there are no mapped views.

There should be no behavioral change here.

src/action.c

@@ -634,7 +634,7 @@ actions_run(struct view *activator, struct server *server,
 			break;
 		case ACTION_TYPE_FOCUS:
 			if (view) {
-				desktop_focus_and_activate_view(&server->seat, view);
+				desktop_focus_view(view);
 			}
 			break;
 		case ACTION_TYPE_ICONIFY:

src/cursor.c

@@ -478,7 +478,7 @@ process_cursor_motion(struct server *server, uint32_t time)
 	}
 
 	if (ctx.view && rc.focus_follow_mouse) {
-		desktop_focus_and_activate_view(seat, ctx.view);
+		desktop_focus_view(ctx.view);
 		if (rc.raise_on_focus) {
 			view_move_to_front(ctx.view);
 		}
@@ -522,7 +522,7 @@ _cursor_update_focus(struct server *server)
 			&& !rc.focus_follow_mouse_requires_movement
 			&& !server->osd_state.cycle_view) {
 		/* Prevents changing keyboard focus during A-Tab */
-		desktop_focus_and_activate_view(&server->seat, ctx.view);
+		desktop_focus_view(ctx.view);
 		if (rc.raise_on_focus) {
 			view_move_to_front(ctx.view);
 		}

src/desktop.c

@@ -35,13 +35,9 @@ desktop_arrange_all_views(struct server *server)
 }
 
 void
-desktop_focus_and_activate_view(struct seat *seat, struct view *view)
+desktop_focus_view(struct view *view)
 {
-	if (!view) {
-		seat_focus_surface(seat, NULL);
-		return;
-	}
-
+	assert(view);
 	/*
 	 * Guard against views with no mapped surfaces when handling
 	 * 'request_activate' and 'request_minimize'.
@@ -51,8 +47,9 @@ desktop_focus_and_activate_view(struct seat *seat, struct view *view)
 		return;
 	}
 
-	if (input_inhibit_blocks_surface(seat, view->surface->resource)
-			|| seat->server->session_lock) {
+	struct server *server = view->server;
+	if (input_inhibit_blocks_surface(&server->seat, view->surface->resource)
+			|| server->session_lock) {
 		return;
 	}
 
@@ -69,16 +66,7 @@ desktop_focus_and_activate_view(struct seat *seat, struct view *view)
 		return;
 	}
 
-	struct wlr_surface *prev_surface;
-	prev_surface = seat->seat->keyboard_state.focused_surface;
-
-	/* Do not re-focus an already focused surface. */
-	if (prev_surface == view->surface) {
-		return;
-	}
-
-	view_set_activated(view);
-	seat_focus_surface(seat, view->surface);
+	view_focus(view);
 }
 
 static struct wl_list *
@@ -210,28 +198,45 @@ struct view *
 desktop_focused_view(struct server *server)
 {
 	struct seat *seat = &server->seat;
-	struct wlr_surface *focused_surface;
-	focused_surface = seat->seat->keyboard_state.focused_surface;
-	if (!focused_surface) {
-		return NULL;
-	}
-	struct view *view;
-	wl_list_for_each(view, &server->views, link) {
-		if (view->surface == focused_surface) {
-			return view;
+	struct wlr_surface *focused_surface =
+		seat->seat->keyboard_state.focused_surface;
+	struct view *focused_view = NULL;
+
+	if (focused_surface) {
+		struct view *view;
+		wl_list_for_each(view, &server->views, link) {
+			if (view->surface == focused_surface) {
+				focused_view = view;
+				break;
+			}
 		}
 	}
 
-	return NULL;
+	/* warn so we can identify cases where this occurs */
+	if (focused_view != server->focused_view) {
+		wlr_log(WLR_ERROR, "server->focused_view is out of sync");
+	}
+
+	return focused_view;
 }
 
 void
 desktop_focus_topmost_mapped_view(struct server *server)
 {
 	struct view *view = desktop_topmost_mapped_view(server);
-	desktop_focus_and_activate_view(&server->seat, view);
 	if (view) {
+		desktop_focus_view(view);
 		view_move_to_front(view);
+	} else {
+		/*
+		 * Defocus previous focused surface/view if no longer
+		 * focusable (e.g. unmapped or on a different workspace).
+		 * Note than a non-view surface may have been focused.
+		 */
+		seat_focus_surface(&server->seat, NULL);
+		if (server->focused_view) {
+			view_defocus(server->focused_view);
+		}
 	}
 }
 
@@ -257,7 +262,7 @@ desktop_focus_output(struct output *output)
 		}
 		if (wlr_output_layout_intersects(layout,
 				output->wlr_output, &view->current)) {
-			desktop_focus_and_activate_view(&output->server->seat, view);
+			desktop_focus_view(view);
 			wlr_cursor_warp(output->server->seat.cursor, NULL,
 				view->current.x + view->current.width / 2,
 				view->current.y + view->current.height / 2);

src/foreign.c

@@ -37,7 +37,7 @@ handle_request_activate(struct wl_listener *listener, void *data)
 	if (view->workspace != view->server->workspace_current) {
 		workspaces_switch_to(view->workspace);
 	}
-	desktop_focus_and_activate_view(&view->server->seat, view);
+	desktop_focus_view(view);
 	view_move_to_front(view);
 }
 

src/keyboard.c

@@ -41,8 +41,8 @@ keyboard_any_modifiers_pressed(struct wlr_keyboard *keyboard)
 static void
 end_cycling(struct server *server)
 {
-	desktop_focus_and_activate_view(&server->seat, server->osd_state.cycle_view);
 	if (server->osd_state.cycle_view) {
+		desktop_focus_view(server->osd_state.cycle_view);
 		view_move_to_front(server->osd_state.cycle_view);
 	}
 

src/view-impl-common.c

@@ -51,7 +51,7 @@ view_impl_move_sub_views(struct view *parent, enum z_direction z_direction)
 void
 view_impl_map(struct view *view)
 {
-	desktop_focus_and_activate_view(&view->server->seat, view);
+	desktop_focus_view(view);
 	view_move_to_front(view);
 	view_update_title(view);
 	view_update_app_id(view);

src/view.c

@@ -187,19 +187,50 @@ _view_set_activated(struct view *view, bool activated)
 	}
 }
 
+/*
+ * Give the view keyboard focus and mark it active. This function should
+ * only be called by desktop_focus_view(), which contains additional
+ * checks to make sure it's okay to give focus.
+ */
 void
-view_set_activated(struct view *view)
+view_focus(struct view *view)
 {
 	assert(view);
-	struct view *last = view->server->focused_view;
-	if (last == view) {
-		return;
+	/* Update seat focus */
+	struct seat *seat = &view->server->seat;
+	if (view->surface != seat->seat->keyboard_state.focused_surface) {
+		seat_focus_surface(seat, view->surface);
 	}
-	if (last) {
-		_view_set_activated(last, false);
+	/* Update active view */
+	if (view != view->server->focused_view) {
+		if (view->server->focused_view) {
+			_view_set_activated(view->server->focused_view, false);
+		}
+		_view_set_activated(view, true);
+		view->server->focused_view = view;
+	}
+}
+
+/*
+ * Take keyboard focus from the view and mark it inactive. It's rarely
+ * necessary to call this function directly; usually it's better to
+ * focus a different view instead by calling something like
+ * desktop_focus_topmost_mapped_view().
+ */
+void
+view_defocus(struct view *view)
+{
+	assert(view);
+	/* Update seat focus */
+	struct seat *seat = &view->server->seat;
+	if (view->surface == seat->seat->keyboard_state.focused_surface) {
+		seat_focus_surface(seat, NULL);
+	}
+	/* Update active view */
+	if (view == view->server->focused_view) {
+		_view_set_activated(view, false);
+		view->server->focused_view = NULL;
 	}
-	_view_set_activated(view, true);
-	view->server->focused_view = view;
 }
 
 void
@@ -377,18 +408,7 @@ _minimize(struct view *view, bool minimized)
 	view->minimized = minimized;
 	if (minimized) {
 		view->impl->unmap(view, /* client_request */ false);
-		_view_set_activated(view, false);
-		if (view == view->server->focused_view) {
-			/*
-			 * Prevents clearing the active view when
-			 * we don't actually have keyboard focus.
-			 *
-			 * This may happen when using a custom mouse
-			 * focus configuration or by using the foreign
-			 * toplevel protocol via some panel.
-			 */
-			view->server->focused_view = NULL;
-		}
+		view_defocus(view);
 	} else {
 		view->impl->map(view);
 	}

src/xdg.c

@@ -615,7 +615,7 @@ xdg_activation_handle_request(struct wl_listener *listener, void *data)
 	if (view->workspace != view->server->workspace_current) {
 		workspaces_switch_to(view->workspace);
 	}
-	desktop_focus_and_activate_view(&view->server->seat, view);
+	desktop_focus_view(view);
 	view_move_to_front(view);
 }
 

src/xwayland.c

@@ -256,7 +256,7 @@ handle_request_activate(struct wl_listener *listener, void *data)
 		return;
 	}
 
-	desktop_focus_and_activate_view(&view->server->seat, view);
+	desktop_focus_view(view);
 	view_move_to_front(view);
 }