Fix TabBar initialization issue and add tests

Author: kitbdev

scene/gui/tab_bar.cpp

@@ -354,6 +354,8 @@ void TabBar::_notification(int p_what) {
 			if (scroll_to_selected) {
 				ensure_tab_visible(current);
 			}
+			// Set initialized even if no tabs were set.
+			initialized = true;
 		} break;
 
 		case NOTIFICATION_INTERNAL_PROCESS: {
@@ -655,10 +657,10 @@ void TabBar::set_tab_count(int p_count) {
 	}
 
 	if (!initialized) {
-		if (queued_current != current) {
-			current = queued_current;
-		}
 		initialized = true;
+		if (queued_current != CURRENT_TAB_UNINITIALIZED && queued_current != current) {
+			set_current_tab(queued_current);
+		}
 	}
 
 	queue_redraw();
@@ -740,6 +742,13 @@ bool TabBar::select_next_available() {
 	return false;
 }
 
+void TabBar::set_tab_offset(int p_offset) {
+	ERR_FAIL_INDEX(p_offset, tabs.size());
+	offset = p_offset;
+	_update_cache();
+	queue_redraw();
+}
+
 int TabBar::get_tab_offset() const {
 	return offset;
 }

scene/gui/tab_bar.h

@@ -117,8 +117,9 @@ class TabBar : public Control {
 	bool scroll_to_selected = true;
 	int tabs_rearrange_group = -1;
 
+	static const int CURRENT_TAB_UNINITIALIZED = -2;
 	bool initialized = false;
-	int queued_current = -1;
+	int queued_current = CURRENT_TAB_UNINITIALIZED;
 
 	const float DEFAULT_GAMEPAD_EVENT_DELAY_MS = 0.5;
 	const float GAMEPAD_EVENT_REPEAT_RATE_MS = 1.0 / 20;
@@ -249,6 +250,7 @@ class TabBar : public Control {
 	bool select_previous_available();
 	bool select_next_available();
 
+	void set_tab_offset(int p_offset);
 	int get_tab_offset() const;
 	bool get_offset_buttons_visible() const;
 

scene/gui/tab_container.cpp

@@ -190,7 +190,7 @@ void TabContainer::_notification(int p_what) {
 		} break;
 
 		case NOTIFICATION_VISIBILITY_CHANGED: {
-			if (!is_visible() || setup_current_tab > -2) {
+			if (!is_visible()) {
 				return;
 			}
 
@@ -200,7 +200,7 @@ void TabContainer::_notification(int p_what) {
 			// beat it to the punch and make sure that the correct node is the only one visible first.
 			// Otherwise, it can prevent a tab change done right before this container was made visible.
 			Vector<Control *> controls = _get_tab_controls();
-			int current = get_current_tab();
+			int current = setup_current_tab > -2 ? setup_current_tab : get_current_tab();
 			for (int i = 0; i < controls.size(); i++) {
 				controls[i]->set_visible(i == current);
 			}