Docking: Fixed reappearing docked windows with no close button showing a tab with extraneous space for one frame.

docs/CHANGELOG.txt

@@ -138,7 +138,8 @@ Docking Branch:
 - Docking: Dockspace() never draws a background. (#3924)
 - Docking: undocking nodes/windows covering most of the monitor max their size down to 90% to ease further manipulations.
 - Docking: Fixed restoring of tab order within a dockspace or a split node.
-- Docking: Fixed multiple simultaneously reappearing window from appearing undocked in their initial frame.
+- Docking: Fixed reappearing docked windows with no close button showing a tab with extraneous space for one frame.
+- Docking: Fixed multiple simultaneously reappearing window from appearing undocked for one frame.
 - Viewports: Hotfix for crash in monitor array access, caused by 4b9bc4902. (#3967)
 - Backends, Viewports: GLFW: Add a workaround for stuck keys after closing a GLFW window (#3837).
 - Backends, Viewports: Vulkan: Rebuild swapchain on VK_SUBOPTIMAL_KHR. (#3881)

imgui.cpp

@@ -16260,7 +16260,12 @@ void ImGui::ShowMetricsWindow(bool* p_open)
     if (TreeNode("TabBars", "Tab Bars (%d)", g.TabBars.GetSize()))
     {
         for (int n = 0; n < g.TabBars.GetSize(); n++)
-            DebugNodeTabBar(g.TabBars.GetByIndex(n), "TabBar");
+        {
+            ImGuiTabBar* tab_bar = g.TabBars.GetByIndex(n);
+            PushID(tab_bar);
+            DebugNodeTabBar(tab_bar, "TabBar");
+            PopID();
+        }
         TreePop();
     }
 
@@ -16702,7 +16707,7 @@ void ImGui::DebugNodeTabBar(ImGuiTabBar* tab_bar, const char* label)
     }
     p += ImFormatString(p, buf_end - p, (tab_bar->Tabs.Size > 3) ? " ... }" : " } ");
     if (!is_active) { PushStyleColor(ImGuiCol_Text, GetStyleColorVec4(ImGuiCol_TextDisabled)); }
-    bool open = TreeNode(tab_bar, "%s", buf);
+    bool open = TreeNode(label, "%s", buf);
     if (!is_active) { PopStyleColor(); }
     if (is_active && IsItemHovered())
     {

imgui_widgets.cpp

@@ -7422,6 +7422,9 @@ void ImGui::TabBarAddTab(ImGuiTabBar* tab_bar, ImGuiTabItemFlags tab_flags, ImGu
     IM_ASSERT(TabBarFindTabByID(tab_bar, window->ID) == NULL);
     IM_ASSERT(g.CurrentTabBar != tab_bar);  // Can't work while the tab bar is active as our tab doesn't have an X offset yet, in theory we could/should test something like (tab_bar->CurrFrameVisible < g.FrameCount) but we'd need to solve why triggers the commented early-out assert in BeginTabBarEx() (probably dock node going from implicit to explicit in same frame)
 
+    if (!window->HasCloseButton)
+        tab_flags |= ImGuiTabItemFlags_NoCloseButton;       // Set _NoCloseButton immediately because it will be used for first-frame width calculation.
+
     ImGuiTabItem new_tab;
     new_tab.ID = window->ID;
     new_tab.Flags = tab_flags;