Demo: Testing return value of BeginTabBar() for consistency.

docs/TODO.txt

@@ -150,7 +150,8 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - dock: C- nav: CTRL+TAB highlighting tabs shows the mismatch between focus-stack and tab-order (not visible in VS because it doesn't highlight the tabs)
  - dock: C- after a dock/undock, the Scrollbar Status update in Begin() should use an updated e.g. size_y_for_scrollbars to avoid a 1 frame scrollbar flicker.
 
- - tabs: re-ordering, close buttons, context menu, persistent order (#261, #351)
+ - tabs: make EndTabBar fail if users doesn't respect BeginTabBar return value, for consistency/future-proofing.
+ - tabs: persistent order/focus in BeginTabBar() api (#261, #351)
 
  - ext: stl-ish friendly extension (imgui_stl.h) that has wrapper for std::string, std::vector etc.
 

imgui_demo.cpp

@@ -1721,7 +1721,8 @@ void ImGui::ShowDemoWindow(bool* p_open)
             if (ImGui::TreeNode("Basic"))
             {
                 ImGuiTabBarFlags tab_bar_flags = ImGuiTabBarFlags_None;
-                ImGui::BeginTabBar("MyTabBar", tab_bar_flags);
+                if (ImGui::BeginTabBar("MyTabBar", tab_bar_flags))
+                {
                     if (ImGui::BeginTabItem("Avocado"))
                     {
                         ImGui::Text("This is the Avocado tab!\nblah blah blah blah blah");
@@ -1738,6 +1739,7 @@ void ImGui::ShowDemoWindow(bool* p_open)
                         ImGui::EndTabItem();
                     }
                     ImGui::EndTabBar();
+                }
                 ImGui::Separator();
                 ImGui::TreePop();
             }
@@ -1766,7 +1768,8 @@ void ImGui::ShowDemoWindow(bool* p_open)
                 }
 
                 // Passing a bool* to BeginTabItem() is similar to passing one to Begin(): the underlying bool will be set to false when the tab is closed.
-                ImGui::BeginTabBar("MyTabBar", tab_bar_flags);
+                if (ImGui::BeginTabBar("MyTabBar", tab_bar_flags))
+                {
                     for (int n = 0; n < IM_ARRAYSIZE(opened); n++)
                         if (opened[n] && ImGui::BeginTabItem(names[n], &opened[n]))
                         {
@@ -1776,6 +1779,7 @@ void ImGui::ShowDemoWindow(bool* p_open)
                             ImGui::EndTabItem();
                         }
                     ImGui::EndTabBar();
+                }
                 ImGui::Separator();
                 ImGui::TreePop();
             }
@@ -3952,8 +3956,8 @@ void ShowExampleAppDocuments(bool* p_open)
     if (opt_target == Target_Tab)
     {
         ImGuiTabBarFlags tab_bar_flags = (opt_fitting_flags) | (opt_reorderable ? ImGuiTabBarFlags_Reorderable : 0);
-        ImGui::BeginTabBar("##tabs", tab_bar_flags);
+        if (ImGui::BeginTabBar("##tabs", tab_bar_flags))
-
+        {
             if (opt_reorderable)
                 NotifyOfDocumentsClosedElsewhere(app);
 
@@ -3988,6 +3992,7 @@ void ShowExampleAppDocuments(bool* p_open)
 
             ImGui::EndTabBar();
         }
+    }
     else if (opt_target == Target_Window)
     {
         if (ImGui::GetIO().ConfigFlags & ImGuiConfigFlags_DockingEnable)