[ainulindale] The Terminal shouldn't crash on a WM_SETTINGCHANGE

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -335,7 +335,7 @@ void AppHost::Initialize()
     _window->DragRegionClicked([this]() { _windowLogic.TitlebarClicked(); });
 
     _window->WindowVisibilityChanged([this](bool showOrHide) { _windowLogic.WindowVisibilityChanged(showOrHide); });
-    _window->UpdateSettingsRequested([this]() { _appLogic.ReloadSettings(); });
+    _window->UpdateSettingsRequested({ this, &AppHost::_requestUpdateSettings });
 
     _revokers.RequestedThemeChanged = _windowLogic.RequestedThemeChanged(winrt::auto_revoke, { this, &AppHost::_UpdateTheme });
     _revokers.FullscreenChanged = _windowLogic.FullscreenChanged(winrt::auto_revoke, { this, &AppHost::_FullscreenChanged });
@@ -1228,3 +1228,11 @@ void AppHost::_handleSendContent(const winrt::Windows::Foundation::IInspectable&
 {
     _windowLogic.SendContentToOther(winrt::TerminalApp::RequestReceiveContentArgs{ args.SourceWindow(), args.TargetWindow(), args.TabIndex() });
 }
+
+// Bubble the update settings request up to the emperor. We're being called on
+// the Window thread, but the Emperor needs to update the settings on the _main_
+// thread.
+void AppHost::_requestUpdateSettings()
+{
+    _UpdateSettingsRequestedHandlers();
+}

src/cascadia/WindowsTerminal/AppHost.h

@@ -26,6 +26,8 @@ class AppHost
 
     static void s_DisplayMessageBox(const winrt::TerminalApp::ParseCommandlineResult& message);
 
+    WINRT_CALLBACK(UpdateSettingsRequested, winrt::delegate<void()>);
+
 private:
     std::unique_ptr<IslandWindow> _window;
 
@@ -123,6 +125,8 @@ class AppHost
     void _handleAttach(const winrt::Windows::Foundation::IInspectable& sender,
                        winrt::Microsoft::Terminal::Remoting::AttachRequest args);
 
+    void _requestUpdateSettings();
+
     // Page -> us -> monarch
     void _handleReceiveContent(const winrt::Windows::Foundation::IInspectable& sender,
                                winrt::TerminalApp::RequestReceiveContentArgs args);

src/cascadia/WindowsTerminal/WindowEmperor.cpp

@@ -122,10 +122,15 @@ void WindowEmperor::CreateNewWindowThread(Remoting::WindowRequestedArgs args, co
         // Add a callback to the window's logic to let us know when the window's
         // quake mode state changes. We'll use this to check if we need to add
         // or remove the notification icon.
-        sender->Logic().IsQuakeWindowChanged([this](auto&&, auto&&) -> winrt::fire_and_forget {
+        sender->Logic().IsQuakeWindowChanged([this](auto&&, auto &&) -> winrt::fire_and_forget {
             co_await wil::resume_foreground(this->_dispatcher);
             this->_checkWindowsForNotificationIcon();
         });
+        sender->UpdateSettingsRequested([this]() -> winrt::fire_and_forget {
+            // We MUST be on the main thread to update the settings. We will crash when trying to enumerate fragement extensions otherwise.
+            co_await wil::resume_foreground(this->_dispatcher);
+            _app.Logic().ReloadSettings();
+        });
 
         // These come in on the sender's thread. Move back to our thread.
         co_await wil::resume_foreground(_dispatcher);

src/cascadia/WindowsTerminal/WindowThread.cpp

@@ -24,7 +24,7 @@ void WindowThread::Start()
                                             _args,
                                             _manager,
                                             _peasant);
-
+        _host->UpdateSettingsRequested([this]() { _UpdateSettingsRequestedHandlers(); });
         // Enter the main window loop.
         const auto exitCode = WindowProc();
         _host = nullptr;

src/cascadia/WindowsTerminal/WindowThread.h

@@ -19,6 +19,7 @@ class WindowThread
 
     WINRT_CALLBACK(Started, winrt::delegate<>);
     WINRT_CALLBACK(Exited, winrt::delegate<uint64_t>);
+    WINRT_CALLBACK(UpdateSettingsRequested, winrt::delegate<void()>);
 
 private:
     winrt::Microsoft::Terminal::Remoting::Peasant _peasant{ nullptr };