From 6dc051dadaa3bb9f6efc070b81e95f6711278313 Mon Sep 17 00:00:00 2001
From: Leonard Hecker <leonard@hecker.io>
Date: Fri, 16 Oct 2020 19:11:47 +0200
Subject: [PATCH] Fixed #5784: Key bindings won't consume dead keys

---
 .../actions/spell-check/dictionary/names.txt  |  2 +
 src/cascadia/TerminalControl/TermControl.cpp  | 40 +++++++++++++++++--
 src/cascadia/TerminalControl/TermControl.h    |  3 +-
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/.github/actions/spell-check/dictionary/names.txt b/.github/actions/spell-check/dictionary/names.txt
index c7f4c1f2b15..23e4f9b6430 100644
--- a/.github/actions/spell-check/dictionary/names.txt
+++ b/.github/actions/spell-check/dictionary/names.txt
@@ -31,9 +31,11 @@ mbadolato
 Mehrain
 mgravell
 michaelniksa
+michkap
 migrie
 mikegr
 mikemaccana
+miloush
 miniksa
 niksa
 oising
diff --git a/src/cascadia/TerminalControl/TermControl.cpp b/src/cascadia/TerminalControl/TermControl.cpp
index 592cd733f7f..fc33c7603c7 100644
--- a/src/cascadia/TerminalControl/TermControl.cpp
+++ b/src/cascadia/TerminalControl/TermControl.cpp
@@ -895,7 +895,7 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
         // keybindings on the keyUp, then we'll still send the keydown to the
         // connected terminal application, and something like ctrl+shift+T will
         // emit a ^T to the pipe.
-        if (!modifiers.IsAltGrPressed() && keyDown && _TryHandleKeyBinding(vkey, modifiers))
+        if (!modifiers.IsAltGrPressed() && keyDown && _TryHandleKeyBinding(vkey, scanCode, modifiers))
         {
             e.Handled(true);
             return;
@@ -917,8 +917,9 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
     // - Attempt to handle this key combination as a key binding
     // Arguments:
     // - vkey: The vkey of the key pressed.
+    // - scanCode: The scan code of the key pressed.
     // - modifiers: The ControlKeyStates representing the modifier key states.
-    bool TermControl::_TryHandleKeyBinding(const WORD vkey, ::Microsoft::Terminal::Core::ControlKeyStates modifiers) const
+    bool TermControl::_TryHandleKeyBinding(const WORD vkey, const WORD scanCode, ::Microsoft::Terminal::Core::ControlKeyStates modifiers) const
     {
         auto bindings = _settings.KeyBindings();
         if (!bindings)
@@ -926,12 +927,44 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
             return false;
         }
 
-        return bindings.TryKeyChord({
+        auto success = bindings.TryKeyChord({
             modifiers.IsCtrlPressed(),
             modifiers.IsAltPressed(),
             modifiers.IsShiftPressed(),
             vkey,
         });
+        if (!success)
+        {
+            return false;
+        }
+
+        // Let's assume the user has bound the dead key "^" to a sendInput command that sends "b".
+        // If the user presses the two keys "^a" it'll produce "bâ", despite us marking the key event as handled.
+        // The following is used to manually "consume" such dead keys and clear them from the keyboard state.
+        _ClearKeyboardState(vkey, scanCode);
+        return true;
+    }
+
+    // Method Description:
+    // - Discards currently pressed dead keys.
+    // Arguments:
+    // - vkey: The vkey of the key pressed.
+    // - scanCode: The scan code of the key pressed.
+    void TermControl::_ClearKeyboardState(const WORD vkey, const WORD scanCode) const noexcept
+    {
+        std::array<BYTE, 256> keyState;
+        if (!GetKeyboardState(keyState.data()))
+        {
+            return;
+        }
+
+        // As described in "Sometimes you *want* to interfere with the keyboard's state buffer":
+        //   http://archives.miloush.net/michkap/archive/2006/09/10/748775.html
+        // > "The key here is to keep trying to pass stuff to ToUnicode until -1 is not returned."
+        std::array<wchar_t, 16> buffer;
+        while (ToUnicodeEx(vkey, scanCode, keyState.data(), buffer.data(), gsl::narrow_cast<int>(buffer.size()), 0b1, nullptr) < 0)
+        {
+        }
     }
 
     // Method Description:
@@ -941,6 +974,7 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
     // - Makes the cursor briefly visible during typing.
     // Arguments:
     // - vkey: The vkey of the key pressed.
+    // - scanCode: The scan code of the key pressed.
     // - states: The Microsoft::Terminal::Core::ControlKeyStates representing the modifier key states.
     // - keyDown: If true, the key was pressed, otherwise the key was released.
     bool TermControl::_TrySendKeyEvent(const WORD vkey,
diff --git a/src/cascadia/TerminalControl/TermControl.h b/src/cascadia/TerminalControl/TermControl.h
index dd1118c3f1c..3d16738e020 100644
--- a/src/cascadia/TerminalControl/TermControl.h
+++ b/src/cascadia/TerminalControl/TermControl.h
@@ -285,7 +285,8 @@ namespace winrt::Microsoft::Terminal::TerminalControl::implementation
 
         void _KeyHandler(Windows::UI::Xaml::Input::KeyRoutedEventArgs const& e, const bool keyDown);
         ::Microsoft::Terminal::Core::ControlKeyStates _GetPressedModifierKeys() const;
-        bool _TryHandleKeyBinding(const WORD vkey, ::Microsoft::Terminal::Core::ControlKeyStates modifiers) const;
+        bool _TryHandleKeyBinding(const WORD vkey, const WORD scanCode, ::Microsoft::Terminal::Core::ControlKeyStates modifiers) const;
+        void _ClearKeyboardState(const WORD vkey, const WORD scanCode) const noexcept;
         bool _TrySendKeyEvent(const WORD vkey, const WORD scanCode, ::Microsoft::Terminal::Core::ControlKeyStates modifiers, const bool keyDown);
         bool _TrySendMouseEvent(Windows::UI::Input::PointerPoint const& point);
         bool _CanSendVTMouseInput();