Try to clone the settings directly from the control

  Okay this is harder, but maybe not impossible, but probably impossible in v1.

  The Profile knows how to build the connection settings, and the
  ControlSettings, etc. However, when the settings reloads like in this bug,
  we'll remove all the old profiles, and build a new list.

  If we wanted the case 1 behavior, we could wait until the Profile is a winrt
  object, then have each Pane hold a strong ref to the Profile that it's
  hosting. Then it would be trivial to be able to duplicate the settings from
  it. I believe that work is tracked in #3998.

  How palatable is doing case 3 now (to fix the crash), then filing a follow up
  to do case 1 once #3998 is done?

Author: zadjii-msft

src/cascadia/LocalTests_TerminalApp/TabTests.cpp

@@ -169,10 +169,11 @@ namespace TerminalAppLocalTests
 
     void TabTests::TryDuplicateBadTab()
     {
-        // Create a tab with a profile with GUID 1
-        // Reload the settings so that GUID 1 is no longer in the list of profiles
-        // Try calling _DuplicateTabViewItem on tab 1
-        // No new tab should be created (and more importantly, the app should not crash)
+        // * Create a tab with a profile with GUID 1
+        // * Reload the settings so that GUID 1 is no longer in the list of profiles
+        // * Try calling _DuplicateTabViewItem on tab 1
+        // * The tab that's created should use the old historySize value from the
+        //   duplicated tab. More importantly, the app should not crash.
         //
         // Created to test GH#2455
 
@@ -249,7 +250,9 @@ namespace TerminalAppLocalTests
         result = RunOnUIThread([&page]() {
             VERIFY_IS_NOT_NULL(page);
             VERIFY_IS_NOT_NULL(page->_settings);
+
             page->Create();
+            Log::Comment(NoThrowString().Format(L"Create()'d"));
 
             // I think in the tests, we don't always set the focused tab on
             // creation. Doesn't seem to be a problem in the real app, but
@@ -258,18 +261,19 @@ namespace TerminalAppLocalTests
             // Manually set it here, so that later, the _GetFocusedTabIndex call
             // in _DuplicateTabViewItem will have a sensible value.
             page->_SetFocusedTabIndex(0);
+            Log::Comment(NoThrowString().Format(L"_SetFocusedTabIndex()'d"));
         });
         VERIFY_SUCCEEDED(result);
 
         result = RunOnUIThread([&page]() {
-            VERIFY_ARE_EQUAL(1u, page->_tabs.size());
+            VERIFY_ARE_EQUAL(1u, page->_tabs.Size());
         });
         VERIFY_SUCCEEDED(result);
 
         Log::Comment(NoThrowString().Format(L"Duplicate the first tab"));
         result = RunOnUIThread([&page]() {
             page->_DuplicateTabViewItem();
-            VERIFY_ARE_EQUAL(2u, page->_tabs.size());
+            VERIFY_ARE_EQUAL(2u, page->_tabs.Size());
         });
         VERIFY_SUCCEEDED(result);
 
@@ -284,7 +288,14 @@ namespace TerminalAppLocalTests
         Log::Comment(NoThrowString().Format(L"Duplicate the tab, and don't crash"));
         result = RunOnUIThread([&page]() {
             page->_DuplicateTabViewItem();
-            VERIFY_ARE_EQUAL(2u, page->_tabs.size(), L"We should gracefully do nothing here - the profile no longer exists.");
+            VERIFY_ARE_EQUAL(3u,
+                             page->_tabs.Size(),
+                             L"We should duplicate the settings of the second "
+                             L"tab here, despite the profile no longer existing");
+
+            auto control = page->_GetStrongTabImpl(2)->GetActiveTerminalControl();
+            VERIFY_IS_NOT_NULL(control);
+            VERIFY_ARE_EQUAL(1, control.Settings().HistorySize());
         });
         VERIFY_SUCCEEDED(result);
     }