Refactor TerminalInput to return strings (#15611)

`TerminalInput` is configurable, but almost entirely state-less.
As such it isn't helpful that it emits its output via a callback.
It makes tracing the flow of data harder purely from reading the code
and also raises uncertainty about when `TerminalInput` may generate
output. This commit makes it more robust by having `TerminalInput`
simply return its data. Furthermore, it returns that data as a string
instead of converting back and forth between text and `IInputEvent`.

This change will help me make conhost's `InputBuffer` implementation
leaner and help me confidently make more difficult changes to it
with the goal to improve our Unicode support/correctness.

## Validation Steps Performed
* Windows Terminal produces correct results with `showkey -a` ✅

.github/actions/spelling/expect/expect.txt

@@ -1031,6 +1031,7 @@ LOGFONT
 LOGFONTA
 LOGFONTW
 logissue
+losslessly
 loword
 lparam
 LPCCH

src/cascadia/TerminalControl/ControlCore.h

@@ -24,8 +24,6 @@
 #include "../buffer/out/search.h"
 #include "../buffer/out/TextColor.h"
 
-#include <til/ticket_lock.h>
-
 namespace ControlUnitTests
 {
     class ControlCoreTests;

src/cascadia/TerminalCore/Terminal.cpp

@@ -21,35 +21,9 @@ using namespace Microsoft::Console::VirtualTerminal;
 
 using PointTree = interval_tree::IntervalTree<til::point, size_t>;
 
-static std::wstring _KeyEventsToText(std::deque<std::unique_ptr<IInputEvent>>& inEventsToWrite)
-{
-    std::wstring wstr = L"";
-    for (const auto& ev : inEventsToWrite)
-    {
-        if (ev->EventType() == InputEventType::KeyEvent)
-        {
-            const auto& k = static_cast<KeyEvent&>(*ev);
-            const auto wch = k.GetCharData();
-            wstr += wch;
-        }
-    }
-    return wstr;
-}
-
 #pragma warning(suppress : 26455) // default constructor is throwing, too much effort to rearrange at this time.
 Terminal::Terminal()
 {
-    auto passAlongInput = [&](std::deque<std::unique_ptr<IInputEvent>>& inEventsToWrite) {
-        if (!_pfnWriteInput)
-        {
-            return;
-        }
-        const auto wstr = _KeyEventsToText(inEventsToWrite);
-        _pfnWriteInput(wstr);
-    };
-
-    _terminalInput = std::make_unique<TerminalInput>(passAlongInput);
-
     _renderSettings.SetColorAlias(ColorAlias::DefaultForeground, TextColor::DEFAULT_FOREGROUND, RGB(255, 255, 255));
     _renderSettings.SetColorAlias(ColorAlias::DefaultBackground, TextColor::DEFAULT_BACKGROUND, RGB(0, 0, 0));
 }
@@ -64,7 +38,7 @@ void Terminal::Create(til::size viewportSize, til::CoordType scrollbackLines, Re
     const UINT cursorSize = 12;
     _mainBuffer = std::make_unique<TextBuffer>(bufferSize, attr, cursorSize, true, renderer);
 
-    auto dispatch = std::make_unique<AdaptDispatch>(*this, renderer, _renderSettings, *_terminalInput);
+    auto dispatch = std::make_unique<AdaptDispatch>(*this, renderer, _renderSettings, _terminalInput);
     auto engine = std::make_unique<OutputStateMachineEngine>(std::move(dispatch));
     _stateMachine = std::make_unique<StateMachine>(std::move(engine));
 
@@ -111,7 +85,7 @@ void Terminal::UpdateSettings(ICoreSettings settings)
     _trimBlockSelection = settings.TrimBlockSelection();
     _autoMarkPrompts = settings.AutoMarkPrompts();
 
-    _terminalInput->ForceDisableWin32InputMode(settings.ForceVTInput());
+    _terminalInput.ForceDisableWin32InputMode(settings.ForceVTInput());
 
     if (settings.TabColor() == nullptr)
     {
@@ -540,7 +514,7 @@ void Terminal::TrySnapOnInput()
 // - true, if we are tracking mouse input. False, otherwise
 bool Terminal::IsTrackingMouseInput() const noexcept
 {
-    return _terminalInput->IsTrackingMouseInput();
+    return _terminalInput.IsTrackingMouseInput();
 }
 
 // Routine Description:
@@ -554,7 +528,7 @@ bool Terminal::IsTrackingMouseInput() const noexcept
 bool Terminal::ShouldSendAlternateScroll(const unsigned int uiButton,
                                          const int32_t delta) const noexcept
 {
-    return _terminalInput->ShouldSendAlternateScroll(uiButton, ::base::saturated_cast<short>(delta));
+    return _terminalInput.ShouldSendAlternateScroll(uiButton, ::base::saturated_cast<short>(delta));
 }
 
 // Method Description:
@@ -741,7 +715,7 @@ bool Terminal::SendKeyEvent(const WORD vkey,
     }
 
     const KeyEvent keyEv{ keyDown, 1, vkey, sc, ch, states.Value() };
-    return _terminalInput->HandleKey(&keyEv);
+    return _handleTerminalInputResult(_terminalInput.HandleKey(&keyEv));
 }
 
 // Method Description:
@@ -765,7 +739,7 @@ bool Terminal::SendMouseEvent(til::point viewportPos, const unsigned int uiButto
     // We shouldn't throw away perfectly good events when they're offscreen, so we just
     // clamp them to be within the range [(0, 0), (W, H)].
     _GetMutableViewport().ToOrigin().Clamp(viewportPos);
-    return _terminalInput->HandleMouse(viewportPos, uiButton, GET_KEYSTATE_WPARAM(states.Value()), wheelDelta, state);
+    return _handleTerminalInputResult(_terminalInput.HandleMouse(viewportPos, uiButton, GET_KEYSTATE_WPARAM(states.Value()), wheelDelta, state));
 }
 
 // Method Description:
@@ -818,7 +792,7 @@ bool Terminal::SendCharEvent(const wchar_t ch, const WORD scanCode, const Contro
     }
 
     const KeyEvent keyDown{ true, 1, vkey, scanCode, ch, states.Value() };
-    return _terminalInput->HandleKey(&keyDown);
+    return _handleTerminalInputResult(_terminalInput.HandleKey(&keyDown));
 }
 
 // Method Description:
@@ -829,9 +803,9 @@ bool Terminal::SendCharEvent(const wchar_t ch, const WORD scanCode, const Contro
 // - focused: true if we're focused, false otherwise.
 // Return Value:
 // - none
-void Terminal::FocusChanged(const bool focused) noexcept
+void Terminal::FocusChanged(const bool focused)
 {
-    _terminalInput->HandleFocus(focused);
+    _handleTerminalInputResult(_terminalInput.HandleFocus(focused));
 }
 
 // Method Description:
@@ -955,6 +929,20 @@ catch (...)
     return UNICODE_INVALID;
 }
 
+[[maybe_unused]] bool Terminal::_handleTerminalInputResult(TerminalInput::OutputType&& out) const
+{
+    if (out)
+    {
+        const auto& str = *out;
+        if (_pfnWriteInput && !str.empty())
+        {
+            _pfnWriteInput(str);
+        }
+        return true;
+    }
+    return false;
+}
+
 // Method Description:
 // - It's possible for a single scan code on a keyboard to
 //   produce different key codes depending on the keyboard state.

src/cascadia/TerminalCore/Terminal.hpp

@@ -156,7 +156,7 @@ class Microsoft::Terminal::Core::Terminal final :
     bool IsTrackingMouseInput() const noexcept;
     bool ShouldSendAlternateScroll(const unsigned int uiButton, const int32_t delta) const noexcept;
 
-    void FocusChanged(const bool focused) noexcept override;
+    void FocusChanged(const bool focused) override;
 
     std::wstring GetHyperlinkAtViewportPosition(const til::point viewportPos);
     std::wstring GetHyperlinkAtBufferPosition(const til::point bufferPos);
@@ -309,7 +309,7 @@ class Microsoft::Terminal::Core::Terminal final :
 
     RenderSettings _renderSettings;
     std::unique_ptr<::Microsoft::Console::VirtualTerminal::StateMachine> _stateMachine;
-    std::unique_ptr<::Microsoft::Console::VirtualTerminal::TerminalInput> _terminalInput;
+    ::Microsoft::Console::VirtualTerminal::TerminalInput _terminalInput;
 
     std::optional<std::wstring> _title;
     std::wstring _startingTitle;
@@ -408,6 +408,7 @@ class Microsoft::Terminal::Core::Terminal final :
     static WORD _VirtualKeyFromCharacter(const wchar_t ch) noexcept;
     static wchar_t _CharacterFromKeyEvent(const WORD vkey, const WORD scanCode, const ControlKeyStates states) noexcept;
 
+    [[maybe_unused]] bool _handleTerminalInputResult(::Microsoft::Console::VirtualTerminal::TerminalInput::OutputType&& out) const;
     void _StoreKeyEvent(const WORD vkey, const WORD scanCode) noexcept;
     WORD _TakeVirtualKeyFromLastKeyEvent(const WORD scanCode) noexcept;
 

src/cascadia/TerminalCore/TerminalApi.cpp

@@ -223,7 +223,7 @@ void Terminal::UseAlternateScreenBuffer(const TextAttribute& attrs)
 
     // GH#3321: Make sure we let the TerminalInput know that we switched
     // buffers. This might affect how we interpret certain mouse events.
-    _terminalInput->UseAlternateScreenBuffer();
+    _terminalInput.UseAlternateScreenBuffer();
 
     // Update scrollbars
     _NotifyScrollEvent();
@@ -277,7 +277,7 @@ void Terminal::UseMainScreenBuffer()
 
     // GH#3321: Make sure we let the TerminalInput know that we switched
     // buffers. This might affect how we interpret certain mouse events.
-    _terminalInput->UseMainScreenBuffer();
+    _terminalInput.UseMainScreenBuffer();
 
     // Update scrollbars
     _NotifyScrollEvent();

src/host/inputBuffer.cpp

@@ -26,13 +26,8 @@ using namespace Microsoft::Console;
 // - A new instance of InputBuffer
 InputBuffer::InputBuffer() :
     InputMode{ INPUT_BUFFER_DEFAULT_INPUT_MODE },
-    WaitQueue{},
-    _pTtyConnection(nullptr),
-    _termInput(std::bind(&InputBuffer::_HandleTerminalInputCallback, this, std::placeholders::_1))
+    _pTtyConnection(nullptr)
 {
-    // The _termInput's constructor takes a reference to this object's _HandleTerminalInputCallback.
-    // We need to use std::bind to create a reference to that function without a reference to this InputBuffer
-
     // initialize buffer header
     fInComposition = false;
 }
@@ -689,7 +684,10 @@ void InputBuffer::WriteFocusEvent(bool focused) noexcept
 {
     if (IsInVirtualTerminalInputMode())
     {
-        _termInput.HandleFocus(focused);
+        if (const auto out = _termInput.HandleFocus(focused))
+        {
+            _HandleTerminalInputCallback(*out);
+        }
     }
     else
     {
@@ -726,7 +724,11 @@ bool InputBuffer::WriteMouseEvent(til::point position, const unsigned int button
         const auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
         gci.GetActiveOutputBuffer().GetViewport().ToOrigin().Clamp(position);
 
-        return _termInput.HandleMouse(position, button, keyState, wheelDelta, state);
+        if (const auto out = _termInput.HandleMouse(position, button, keyState, wheelDelta, state))
+        {
+            _HandleTerminalInputCallback(*out);
+            return true;
+        }
     }
 
     return false;
@@ -765,10 +767,9 @@ void InputBuffer::_WriteBuffer(_Inout_ std::deque<std::unique_ptr<IInputEvent>>&
         inEvents.pop_front();
         if (vtInputMode)
         {
-            // GH#11682: TerminalInput::HandleKey can handle both KeyEvents and Focus events seamlessly
-            const auto handled = _termInput.HandleKey(inEvent.get());
-            if (handled)
+            if (const auto out = _termInput.HandleKey(inEvent.get()))
             {
+                _HandleTerminalInputCallback(*out);
                 eventsWritten++;
                 continue;
             }
@@ -994,16 +995,18 @@ bool InputBuffer::IsInVirtualTerminalInputMode() const
 // - inEvents - Series of input records to insert into the buffer
 // Return Value:
 // - <none>
-void InputBuffer::_HandleTerminalInputCallback(std::deque<std::unique_ptr<IInputEvent>>& inEvents)
+void InputBuffer::_HandleTerminalInputCallback(const TerminalInput::StringType& text)
 {
     try
     {
-        // add all input events to the storage queue
-        while (!inEvents.empty())
+        if (text.empty())
         {
-            auto inEvent = std::move(inEvents.front());
-            inEvents.pop_front();
-            _storage.push_back(std::move(inEvent));
+            return;
+        }
+
+        for (const auto& wch : text)
+        {
+            _storage.push_back(std::make_unique<KeyEvent>(true, 1ui16, 0ui16, 0ui16, wch, 0));
         }
 
         if (!_vtInputShouldSuppress)

src/host/inputBuffer.hpp

@@ -128,7 +128,7 @@ class InputBuffer final : public ConsoleObjectHeader
     bool _CoalesceRepeatedKeyPressEvents(_Inout_ std::deque<std::unique_ptr<IInputEvent>>& inEvents);
     void _HandleConsoleSuspensionEvents(_Inout_ std::deque<std::unique_ptr<IInputEvent>>& inEvents);
 
-    void _HandleTerminalInputCallback(_In_ std::deque<std::unique_ptr<IInputEvent>>& inEvents);
+    void _HandleTerminalInputCallback(const Microsoft::Console::VirtualTerminal::TerminalInput::StringType& text);
 
 #ifdef UNIT_TESTING
     friend class InputBufferTests;