Docking: Fix undocking (#3243), amend 7b3d3798 (#1738)

imgui.cpp

@@ -6796,9 +6796,14 @@ void ImGui::FocusWindow(ImGuiWindow* window)
     IM_ASSERT(window == NULL || window->RootWindow != NULL);
     ImGuiWindow* focus_front_window = window ? window->RootWindowDockStop : NULL;
     ImGuiWindow* display_front_window = window ? window->RootWindow : NULL;
-
-    // Steal focus on active widgets
-    if (g.ActiveId != 0 && g.ActiveIdWindow && g.ActiveIdWindow->RootWindowDockStop != focus_front_window)
+    ImGuiDockNode* dock_node = window ? window->DockNode : NULL;
+    bool active_id_window_is_dock_node_host = (g.ActiveIdWindow && dock_node && dock_node->HostWindow == g.ActiveIdWindow);
+
+    // Steal active widgets. Some of the cases it triggers includes:
+    // - Focus a window while an InputText in another window is active, if focus happens before the old InputText can run.
+    // - When using Nav to activate menu items (due to timing of activating on press->new window appears->losing ActiveId)
+    // - Using dock host items (tab, collapse button) can trigger this before we redirect the ActiveIdWindow toward the child window.
+    if (g.ActiveId != 0 && g.ActiveIdWindow && g.ActiveIdWindow->RootWindowDockStop != focus_front_window && !active_id_window_is_dock_node_host)
         ClearActiveID();
 
     // Passing NULL allow to disable keyboard focus
@@ -6807,8 +6812,8 @@ void ImGui::FocusWindow(ImGuiWindow* window)
     window->LastFrameJustFocused = g.FrameCount;
 
     // Select in dock node
-    if (window->DockNode && window->DockNode->TabBar)
-        window->DockNode->TabBar->SelectedTabId = window->DockNode->TabBar->NextSelectedTabId = window->ID;
+    if (dock_node && dock_node->TabBar)
+        dock_node->TabBar->SelectedTabId = dock_node->TabBar->NextSelectedTabId = window->ID;
 
     // Bring to front
     BringWindowToFocusFront(focus_front_window);

imgui_widgets.cpp

@@ -7289,6 +7289,11 @@ bool    ImGui::TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open,
         tab_bar->NextSelectedTabId = id;
     hovered |= (g.HoveredId == id);
 
+    // Transfer active id window so the active id is not owned by the dock host (as StartMouseMovingWindow()
+    // will only do it on the drag). This allows FocusWindow() to be more conservative in how it clears active id.
+    if (held && docked_window && g.ActiveId == id && g.ActiveIdIsJustActivated)
+        g.ActiveIdWindow = docked_window;
+
     // Allow the close button to overlap unless we are dragging (in which case we don't want any overlapping tabs to be hovered)
     if (!held)
         SetItemAllowOverlap();