Fix C-M-z, C-M-x in Conpty (#4940)

## Summary of the Pull Request

This PR ensures that Conpty properly treats `^[^Z` and `^[^X` as
<kbd>Ctrl+Alt+z</kbd> and <kbd>Ctrl+Alt+x</kbd>, instead of <kbd>Ctrl+z</kbd>
and <kbd>Ctrl+x</kbd>.

## References

## PR Checklist
* [x] Closes #4201
* [x] I work here
* [x] Tests added/passed
* [n/a] Requires documentation to be updated

## Detailed Description of the Pull Request / Additional comments

`^Z` and `^X` are special control characters, SUB and CAN. For the output state
machine, these characters are supposed to be executed from _any_ state. However,
we shouldn't do this for the input engine. With the current behavior, these
characters are immediately executed regardless of what state we're in. That
means we end up synthesizing <kbd>Ctrl+z/x</kbd> for these characters. However,
for the InputStateMachine engine, when these characters are preceeded by `^[`
(ESC), we want to treat them as <kbd>Ctrl+Alt+z/x</kbd>.

This just adds a check in `StateMachine` to see if we should immediately execute
these characters from any state, similar to many of the other exceptions we
already perform in the StateMachine for the input engine.

## Validation Steps Performed
* ran tests
* checked `showkey -a` in gnome-terminal
* checked `showkey -a` in conhost
* checked `showkey -a` in vt pipeterm (conhost as a conpty terminal)
* checked `showkey -a` in Windows Terminal

doc/cascadia/SettingsSchema.md

@@ -110,31 +110,31 @@ For commands with arguments:
 
 | Command | Command Description | Action (*=required) | Action Arguments | Argument Descriptions |
 | ------- | ------------------- | ------ | ---------------- | ----------------- |
-| closePane | Close the active pane. | | | |
-| closeTab | Close the current tab. | | | |
-| closeWindow | Close the current window and all tabs within it. | | | |
-| copy | Copy the selected terminal content to your Windows Clipboard. | `trimWhitespace` | boolean | When `true`, newlines persist from the selected text. When `false`, copied content will paste on one line. |
-| decreaseFontSize | Make the text smaller by one delta. | `delta` | integer | Amount of size decrease per command invocation. |
-| duplicateTab | Make a copy and open the current tab. | | | |
-| find | Open the search dialog box. | | | |
-| increaseFontSize | Make the text larger by one delta. | `delta` | integer | Amount of size increase per command invocation. |
-| moveFocus | Focus on a different pane depending on direction. | `direction`* | `left`, `right`, `up`, `down` | Direction in which the focus will move. |
-| newTab | Create a new tab. Without any arguments, this will open the default profile in a new tab. | 1. `commandLine`<br>2. `startingDirectory`<br>3. `tabTitle`<br>4. `index`<br>5. `profile` | 1. string<br>2. string<br>3. string<br>4. integer<br>5. string | 1. Executable run within the tab.<br>2. Directory in which the tab will open.<br>3. Title of the new tab.<br>4. Profile that will open based on its position in the dropdown (starting at 0).<br>5. Profile that will open based on its GUID or name. |
-| nextTab | Open the tab to the right of the current one. | | | |
-| openNewTabDropdown | Open the dropdown menu. | | | |
-| openSettings | Open the settings file. | | | |
-| paste | Insert the content that was copied onto the clipboard. | | | |
-| prevTab | Open the tab to the left of the current one. | | | |
-| resetFontSize | Reset the text size to the default value. | | | |
-| resizePane | Change the size of the active pane. | `direction`* | `left`, `right`, `up`, `down` | Direction in which the pane will be resized. |
-| scrollDown | Move the screen down. | | | |
-| scrollUp | Move the screen up. | | | |
-| scrollUpPage | Move the screen up a whole page. | | | |
-| scrollDownPage | Move the screen down a whole page. | | | |
-| splitPane | Halve the size of the active pane and open another. Without any arguments, this will open the default profile in the new pane. | 1. `split`*<br>2. `commandLine`<br>3. `startingDirectory`<br>4. `tabTitle`<br>5. `index`<br>6. `profile` | 1. `vertical`, `horizontal`, `auto`<br>2. string<br>3. string<br>4. string<br>5. integer<br>6. string | 1. How the pane will split. `auto` will split in the direction that provides the most surface area.<br>2. Executable run within the pane.<br>3. Directory in which the pane will open.<br>4. Title of the tab when the new pane is focused.<br>5. Profile that will open based on its position in the dropdown (starting at 0).<br>6. Profile that will open based on its GUID or name. |
-| switchToTab | Open a specific tab depending on index. | `index`* | integer | Tab that will open based on its position in the tab bar (starting at 0). |
-| toggleFullscreen | Switch between fullscreen and default window sizes. | | | |
-| unbound | Unbind the associated keys from any command. | | | |
+| `closePane` | Close the active pane. | | | |
+| `closeTab` | Close the current tab. | | | |
+| `closeWindow` | Close the current window and all tabs within it. | | | |
+| `copy` | Copy the selected terminal content to your Windows Clipboard. | `trimWhitespace` | boolean | When `true`, newlines persist from the selected text. When `false`, copied content will paste on one line. |
+| `decreaseFontSize` | Make the text smaller by one delta. | `delta` | integer | Amount of size decrease per command invocation. |
+| `duplicateTab` | Make a copy and open the current tab. | | | |
+| `find` | Open the search dialog box. | | | |
+| `increaseFontSize` | Make the text larger by one delta. | `delta` | integer | Amount of size increase per command invocation. |
+| `moveFocus` | Focus on a different pane depending on direction. | `direction`* | `left`, `right`, `up`, `down` | Direction in which the focus will move. |
+| `newTab` | Create a new tab. Without any arguments, this will open the default profile in a new tab. | 1. `commandLine`<br>2. `startingDirectory`<br>3. `tabTitle`<br>4. `index`<br>5. `profile` | 1. string<br>2. string<br>3. string<br>4. integer<br>5. string | 1. Executable run within the tab.<br>2. Directory in which the tab will open.<br>3. Title of the new tab.<br>4. Profile that will open based on its position in the dropdown (starting at 0).<br>5. Profile that will open based on its GUID or name. |
+| `nextTab` | Open the tab to the right of the current one. | | | |
+| `openNewTabDropdown` | Open the dropdown menu. | | | |
+| `openSettings` | Open the settings file. | | | |
+| `paste` | Insert the content that was copied onto the clipboard. | | | |
+| `prevTab` | Open the tab to the left of the current one. | | | |
+| `resetFontSize` | Reset the text size to the default value. | | | |
+| `resizePane` | Change the size of the active pane. | `direction`* | `left`, `right`, `up`, `down` | Direction in which the pane will be resized. |
+| `scrollDown` | Move the screen down. | | | |
+| `scrollUp` | Move the screen up. | | | |
+| `scrollUpPage` | Move the screen up a whole page. | | | |
+| `scrollDownPage` | Move the screen down a whole page. | | | |
+| `splitPane` | Halve the size of the active pane and open another. Without any arguments, this will open the default profile in the new pane. | 1. `split`*<br>2. `commandLine`<br>3. `startingDirectory`<br>4. `tabTitle`<br>5. `index`<br>6. `profile` | 1. `vertical`, `horizontal`, `auto`<br>2. string<br>3. string<br>4. string<br>5. integer<br>6. string | 1. How the pane will split. `auto` will split in the direction that provides the most surface area.<br>2. Executable run within the pane.<br>3. Directory in which the pane will open.<br>4. Title of the tab when the new pane is focused.<br>5. Profile that will open based on its position in the dropdown (starting at 0).<br>6. Profile that will open based on its GUID or name. |
+| `switchToTab` | Open a specific tab depending on index. | `index`* | integer | Tab that will open based on its position in the tab bar (starting at 0). |
+| `toggleFullscreen` | Switch between fullscreen and default window sizes. | | | |
+| `unbound` | Unbind the associated keys from any command. | | | |
 
 ### Accepted Modifiers and Keys
 

src/terminal/parser/stateMachine.cpp

@@ -1167,8 +1167,13 @@ void StateMachine::ProcessCharacter(const wchar_t wch)
     _trace.TraceCharInput(wch);
 
     // Process "from anywhere" events first.
-    if (wch == AsciiChars::CAN ||
-        wch == AsciiChars::SUB)
+    const bool isFromAnywhereChar = (wch == AsciiChars::CAN || wch == AsciiChars::SUB);
+
+    // GH#4201 - If this sequence was ^[^X or ^[^Z, then we should
+    // _ActionExecuteFromEscape, as to send a Ctrl+Alt+key key. We should only
+    // do this for the InputStateMachineEngine - the OutputEngine should execute
+    // these from any state.
+    if (isFromAnywhereChar && !(_state == VTStates::Escape && _engine->DispatchControlCharsFromEscape()))
     {
         _ActionExecute(wch);
         _EnterGround();

src/terminal/parser/ut_parser/InputEngineTest.cpp

@@ -259,6 +259,7 @@ class Microsoft::Console::VirtualTerminal::InputEngineTest
     TEST_METHOD(SGRMouseTest_Modifiers);
     TEST_METHOD(SGRMouseTest_Movement);
     TEST_METHOD(SGRMouseTest_Scroll);
+    TEST_METHOD(CtrlAltZCtrlAltXTest);
 
     friend class TestInteractDispatch;
 };
@@ -1141,3 +1142,68 @@ void InputEngineTest::SGRMouseTest_Scroll()
     // clang-format on
     VerifySGRMouseData(testData);
 }
+
+void InputEngineTest::CtrlAltZCtrlAltXTest()
+{
+    auto pfn = std::bind(&TestState::TestInputCallback, &testState, std::placeholders::_1);
+
+    auto dispatch = std::make_unique<TestInteractDispatch>(pfn, &testState);
+    auto inputEngine = std::make_unique<InputStateMachineEngine>(std::move(dispatch));
+    auto _stateMachine = std::make_unique<StateMachine>(std::move(inputEngine));
+    VERIFY_IS_NOT_NULL(_stateMachine);
+    testState._stateMachine = _stateMachine.get();
+
+    // This is a test for GH#4201. See that issue for more details.
+    Log::Comment(L"Test Ctrl+Alt+Z and Ctrl+Alt+X, which execute from anywhere "
+                 L"in the output engine, but should be Escape-Executed in the "
+                 L"input engine.");
+
+    DisableVerifyExceptions disable;
+
+    {
+        auto inputSeq = L"\x1b\x1a"; // ^[^Z
+
+        wchar_t expectedWch = L'Z';
+        short keyscan = VkKeyScanW(expectedWch);
+        short vkey = keyscan & 0xff;
+        WORD scanCode = (WORD)MapVirtualKeyW(vkey, MAPVK_VK_TO_VSC);
+
+        INPUT_RECORD inputRec;
+
+        inputRec.EventType = KEY_EVENT;
+        inputRec.Event.KeyEvent.bKeyDown = TRUE;
+        inputRec.Event.KeyEvent.dwControlKeyState = LEFT_ALT_PRESSED | LEFT_CTRL_PRESSED;
+        inputRec.Event.KeyEvent.wRepeatCount = 1;
+        inputRec.Event.KeyEvent.wVirtualKeyCode = vkey;
+        inputRec.Event.KeyEvent.wVirtualScanCode = scanCode;
+        inputRec.Event.KeyEvent.uChar.UnicodeChar = expectedWch - 0x40;
+
+        testState.vExpectedInput.push_back(inputRec);
+
+        _stateMachine->ProcessString(inputSeq);
+    }
+    {
+        auto inputSeq = L"\x1b\x18"; // ^[^X
+
+        wchar_t expectedWch = L'X';
+        short keyscan = VkKeyScanW(expectedWch);
+        short vkey = keyscan & 0xff;
+        WORD scanCode = (WORD)MapVirtualKeyW(vkey, MAPVK_VK_TO_VSC);
+
+        INPUT_RECORD inputRec;
+
+        inputRec.EventType = KEY_EVENT;
+        inputRec.Event.KeyEvent.bKeyDown = TRUE;
+        inputRec.Event.KeyEvent.dwControlKeyState = LEFT_ALT_PRESSED | LEFT_CTRL_PRESSED;
+        inputRec.Event.KeyEvent.wRepeatCount = 1;
+        inputRec.Event.KeyEvent.wVirtualKeyCode = vkey;
+        inputRec.Event.KeyEvent.wVirtualScanCode = scanCode;
+        inputRec.Event.KeyEvent.uChar.UnicodeChar = expectedWch - 0x40;
+
+        testState.vExpectedInput.push_back(inputRec);
+
+        _stateMachine->ProcessString(inputSeq);
+    }
+
+    VerifyExpectedInputDrained();
+}