Drag and Drop, Nav: Disabling navigation arrow keys when drag and drop is active. (#3025)

docs/CHANGELOG.txt

@@ -36,6 +36,8 @@ HOW TO UPDATE?
 
 Other Changes:
 
+- Drag and Drop, Nav: Disabling navigation arrow keys when drag and drop is active. In the docking
+  branch pressing arrow keys while dragging a window from a tab could trigger an assert. (#3025)
 - ColorButton: Added ImGuiColorEditFlags_NoBorder flag to remove the border normally enforced
   by default for standalone ColorButton.
 - InputText: Fixed password fields displaying ASCII spaces as blanks instead of using the '*'

imgui.cpp

@@ -3254,6 +3254,9 @@ void ImGui::StartMouseMovingWindow(ImGuiWindow* window)
 
 // Handle mouse moving window
 // Note: moving window with the navigation keys (Square + d-pad / CTRL+TAB + Arrows) are processed in NavUpdateWindowing()
+// FIXME: We don't have strong guarantee that g.MovingWindow stay synched with g.ActiveId == g.MovingWindow->MoveId.
+// This is currently enforced by the fact that BeginDragDropSource() is setting all g.ActiveIdUsingXXXX flags to inhibit navigation inputs,
+// but if we should more thoroughly test cases where g.ActiveId or g.MovingWindow gets changed and not the other.
 void ImGui::UpdateMouseMovingWindowNewFrame()
 {
     ImGuiContext& g = *GImGui;
@@ -8999,6 +9002,11 @@ bool ImGui::BeginDragDropSource(ImGuiDragDropFlags flags)
             return false;
         source_parent_id = window->IDStack.back();
         source_drag_active = IsMouseDragging(mouse_button);
+
+        // Disable navigation and key inputs while dragging
+        g.ActiveIdUsingNavDirMask = ~(ImU32)0;
+        g.ActiveIdUsingNavInputMask = ~(ImU32)0;
+        g.ActiveIdUsingKeyInputMask = ~(ImU64)0;
     }
     else
     {