Add support for the BEL control in Windows Terminal (#7679)

This commit makes the Windows Terminal play an audible sound when the
`BEL` control character is output.

The `BEL` control was already being forwarded through conpty, so it was
just a matter of hooking up the `WarningBell` dispatch method to
actually play a sound. I've used the `PlaySound` API to output the sound
configured for the "Critical Stop" system event (aka _SystemHand_),
since that is the sound used in conhost.

## Validation

I've manually confirmed that the terminal produces the expected sound
when executing `echo ^G` in a cmd shell, or `printf "\a"` in a WSL bash
shell.

References:
* There is a separate issue (#1608) to deal with configuring the `BEL`
  to trigger visual forms of notification.
* There is also an issue (#2360) requesting an option to disable the
  `BEL`.

Closes #4046

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -8,6 +8,7 @@
 #include "AppLogic.h"
 #include "../../types/inc/utils.hpp"
 
+#include <Mmsystem.h>
 #include <LibraryResources.h>
 
 #include "TerminalPage.g.cpp"
@@ -1141,6 +1142,8 @@ namespace winrt::TerminalApp::implementation
         // Add an event handler when the terminal wants to paste data from the Clipboard.
         term.PasteFromClipboard({ this, &TerminalPage::_PasteFromClipboardHandler });
 
+        term.WarningBell({ this, &TerminalPage::_WarningBellHandler });
+
         term.OpenHyperlink({ this, &TerminalPage::_OpenHyperlinkHandler });
 
         // Bind Tab events to the TermControl and the Tab's Pane
@@ -1801,6 +1804,18 @@ namespace winrt::TerminalApp::implementation
         CATCH_LOG();
     }
 
+    // Method Description:
+    // - Plays a warning note when triggered by the BEL control character,
+    //   using the sound configured for the "Critical Stop" system event.
+    //   This matches the behavior of the Windows Console host.
+    // Arguments:
+    // - <none>
+    void TerminalPage::_WarningBellHandler(const IInspectable sender, const IInspectable eventArgs)
+    {
+        const auto soundAlias = reinterpret_cast<LPCTSTR>(SND_ALIAS_SYSTEMHAND);
+        PlaySound(soundAlias, NULL, SND_ALIAS_ID | SND_ASYNC | SND_SENTRY);
+    }
+
     void TerminalPage::_OpenHyperlinkHandler(const IInspectable /*sender*/, const Microsoft::Terminal::TerminalControl::OpenHyperlinkEventArgs eventArgs)
     {
         try

src/cascadia/TerminalApp/TerminalPage.h

@@ -176,6 +176,7 @@ namespace winrt::TerminalApp::implementation
         winrt::fire_and_forget _PasteFromClipboardHandler(const IInspectable sender,
                                                           const Microsoft::Terminal::TerminalControl::PasteFromClipboardEventArgs eventArgs);
 
+        void _WarningBellHandler(const IInspectable sender, const IInspectable eventArgs);
         void _OpenHyperlinkHandler(const IInspectable sender, const Microsoft::Terminal::TerminalControl::OpenHyperlinkEventArgs eventArgs);
         void _ShowCouldNotOpenDialog(winrt::hstring reason, winrt::hstring uri);
         bool _CopyText(const bool singleLine, const Windows::Foundation::IReference<Microsoft::Terminal::TerminalControl::CopyFormat>& formats);

src/cascadia/TerminalControl/TermControl.cpp

@@ -83,6 +83,9 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
 
         _terminal = std::make_unique<::Microsoft::Terminal::Core::Terminal>();
 
+        auto pfnWarningBell = std::bind(&TermControl::_TerminalWarningBell, this);
+        _terminal->SetWarningBellCallback(pfnWarningBell);
+
         auto pfnTitleChanged = std::bind(&TermControl::_TerminalTitleChanged, this, std::placeholders::_1);
         _terminal->SetTitleChangedCallback(pfnTitleChanged);
 
@@ -2172,6 +2175,11 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
         }
     }
 
+    void TermControl::_TerminalWarningBell()
+    {
+        _WarningBellHandlers(*this, nullptr);
+    }
+
     void TermControl::_TerminalTitleChanged(const std::wstring_view& wstr)
     {
         _titleChangedHandlers(winrt::hstring{ wstr });

src/cascadia/TerminalControl/TermControl.h

@@ -149,6 +149,7 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
         DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(CopyToClipboard,     _clipboardCopyHandlers,     TerminalControl::TermControl, TerminalControl::CopyToClipboardEventArgs);
         DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(OpenHyperlink, _openHyperlinkHandlers, TerminalControl::TermControl, TerminalControl::OpenHyperlinkEventArgs);
 
+        TYPED_EVENT(WarningBell, IInspectable, IInspectable);
         TYPED_EVENT(ConnectionStateChanged, TerminalControl::TermControl, IInspectable);
         TYPED_EVENT(Initialized, TerminalControl::TermControl, Windows::UI::Xaml::RoutedEventArgs);
         TYPED_EVENT(TabColorChanged, IInspectable, IInspectable);
@@ -261,6 +262,7 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
         void _SwapChainScaleChanged(Windows::UI::Xaml::Controls::SwapChainPanel const& sender, Windows::Foundation::IInspectable const& args);
         void _DoResizeUnderLock(const double newWidth, const double newHeight);
         void _RefreshSizeUnderLock();
+        void _TerminalWarningBell();
         void _TerminalTitleChanged(const std::wstring_view& wstr);
         void _TerminalTabColorChanged(const std::optional<til::color> color);
         void _CopyToClipboard(const std::wstring_view& wstr);

src/cascadia/TerminalControl/TermControl.idl

@@ -60,6 +60,7 @@ namespace Microsoft.Terminal.TerminalControl
         event Windows.Foundation.TypedEventHandler<TermControl, CopyToClipboardEventArgs> CopyToClipboard;
         event Windows.Foundation.TypedEventHandler<TermControl, PasteFromClipboardEventArgs> PasteFromClipboard;
         event Windows.Foundation.TypedEventHandler<TermControl, OpenHyperlinkEventArgs> OpenHyperlink;
+        event Windows.Foundation.TypedEventHandler<Object, Object> WarningBell;
 
         event Windows.Foundation.TypedEventHandler<TermControl, Windows.UI.Xaml.RoutedEventArgs> Initialized;
         // This is an event handler forwarder for the underlying connection.

src/cascadia/TerminalCore/ITerminalApi.hpp

@@ -34,6 +34,7 @@ namespace Microsoft::Terminal::Core
         virtual bool EraseInLine(const ::Microsoft::Console::VirtualTerminal::DispatchTypes::EraseType eraseType) noexcept = 0;
         virtual bool EraseInDisplay(const ::Microsoft::Console::VirtualTerminal::DispatchTypes::EraseType eraseType) noexcept = 0;
 
+        virtual bool WarningBell() noexcept = 0;
         virtual bool SetWindowTitle(std::wstring_view title) noexcept = 0;
 
         virtual bool SetColorTableEntry(const size_t tableIndex, const DWORD color) noexcept = 0;

src/cascadia/TerminalCore/Terminal.cpp

@@ -965,6 +965,11 @@ void Terminal::SetWriteInputCallback(std::function<void(std::wstring&)> pfn) noe
     _pfnWriteInput.swap(pfn);
 }
 
+void Terminal::SetWarningBellCallback(std::function<void()> pfn) noexcept
+{
+    _pfnWarningBell.swap(pfn);
+}
+
 void Terminal::SetTitleChangedCallback(std::function<void(const std::wstring_view&)> pfn) noexcept
 {
     _pfnTitleChanged.swap(pfn);

src/cascadia/TerminalCore/Terminal.hpp

@@ -90,6 +90,7 @@ class Microsoft::Terminal::Core::Terminal final :
     bool EraseCharacters(const size_t numChars) noexcept override;
     bool EraseInLine(const ::Microsoft::Console::VirtualTerminal::DispatchTypes::EraseType eraseType) noexcept override;
     bool EraseInDisplay(const ::Microsoft::Console::VirtualTerminal::DispatchTypes::EraseType eraseType) noexcept override;
+    bool WarningBell() noexcept override;
     bool SetWindowTitle(std::wstring_view title) noexcept override;
     bool SetColorTableEntry(const size_t tableIndex, const COLORREF color) noexcept override;
     bool SetCursorStyle(const ::Microsoft::Console::VirtualTerminal::DispatchTypes::CursorStyle cursorStyle) noexcept override;
@@ -175,6 +176,7 @@ class Microsoft::Terminal::Core::Terminal final :
 #pragma endregion
 
     void SetWriteInputCallback(std::function<void(std::wstring&)> pfn) noexcept;
+    void SetWarningBellCallback(std::function<void()> pfn) noexcept;
     void SetTitleChangedCallback(std::function<void(const std::wstring_view&)> pfn) noexcept;
     void SetTabColorChangedCallback(std::function<void(const std::optional<til::color>)> pfn) noexcept;
     void SetCopyToClipboardCallback(std::function<void(const std::wstring_view&)> pfn) noexcept;
@@ -207,6 +209,7 @@ class Microsoft::Terminal::Core::Terminal final :
 
 private:
     std::function<void(std::wstring&)> _pfnWriteInput;
+    std::function<void()> _pfnWarningBell;
     std::function<void(const std::wstring_view&)> _pfnTitleChanged;
     std::function<void(const std::wstring_view&)> _pfnCopyToClipboard;
     std::function<void(const int, const int, const int)> _pfnScrollPositionChanged;

src/cascadia/TerminalCore/TerminalApi.cpp

@@ -345,6 +345,14 @@ try
 }
 CATCH_LOG_RETURN_FALSE()
 
+bool Terminal::WarningBell() noexcept
+try
+{
+    _pfnWarningBell();
+    return true;
+}
+CATCH_LOG_RETURN_FALSE()
+
 bool Terminal::SetWindowTitle(std::wstring_view title) noexcept
 try
 {

src/cascadia/TerminalCore/TerminalDispatch.cpp

@@ -109,6 +109,13 @@ try
 }
 CATCH_LOG_RETURN_FALSE()
 
+bool TerminalDispatch::WarningBell() noexcept
+try
+{
+    return _terminalApi.WarningBell();
+}
+CATCH_LOG_RETURN_FALSE()
+
 bool TerminalDispatch::CarriageReturn() noexcept
 try
 {

src/cascadia/TerminalCore/TerminalDispatch.hpp

@@ -30,6 +30,7 @@ class TerminalDispatch : public Microsoft::Console::VirtualTerminal::TermDispatc
     bool LineFeed(const ::Microsoft::Console::VirtualTerminal::DispatchTypes::LineFeedType lineFeedType) noexcept override;
 
     bool EraseCharacters(const size_t numChars) noexcept override;
+    bool WarningBell() noexcept override;
     bool CarriageReturn() noexcept override;
     bool SetWindowTitle(std::wstring_view title) noexcept override;