Add support for Ctrl+# keys (#4938)

## Summary of the Pull Request

Fixes the <kbd>Ctrl+Num</kbd> keys in both conhost and the Terminal. These keys are supposed to be mapped to specific characters according to [this doc](https://vt100.net/docs/vt220-rm/table3-5.html). Now we actually handle them correctly.

## PR Checklist
* [x] Closes #3507 
* [x] I work here
* [x] Tests added/passed
* [n/a] Requires documentation to be updated

## Validation Steps Performed

* Ran test
* tested in `gnome-terminal` with `showkeys -a`
* tested in conhost with `showkeys -a`
* tested in Windows Terminal with `showkeys -a`

src/terminal/adapter/ut_adapter/inputTest.cpp

@@ -45,6 +45,7 @@ class Microsoft::Console::VirtualTerminal::InputTest
     TEST_METHOD(TerminalInputModifierKeyTests);
     TEST_METHOD(TerminalInputNullKeyTests);
     TEST_METHOD(DifferentModifiersTest);
+    TEST_METHOD(CtrlNumTest);
 
     wchar_t GetModifierChar(const bool fShift, const bool fAlt, const bool fCtrl)
     {
@@ -511,6 +512,13 @@ void InputTest::TerminalInputModifierKeyTests()
                 s_pwsInputBuffer[1] = wchShifted;
                 fExpectedKeyHandled = true;
             }
+            else if (ControlPressed(uiKeystate) && (vkey >= '1' && vkey <= '9'))
+            {
+                // The C-# keys get translated into very specific control
+                // characters that don't play nicely with this test. These keys
+                // are tested in the CtrlNumTest Test instead.
+                continue;
+            }
             else
             {
                 fExpectedKeyHandled = false;
@@ -714,3 +722,49 @@ void InputTest::DifferentModifiersTest()
     // LEFT_CTRL_PRESSED | RIGHT_ALT_PRESSED is skipped because that's AltGr
     TestKey(pInput, SHIFT_PRESSED | RIGHT_CTRL_PRESSED | RIGHT_ALT_PRESSED, vkey, L'?');
 }
+
+void InputTest::CtrlNumTest()
+{
+    Log::Comment(L"Starting test...");
+
+    const TerminalInput* const pInput = new TerminalInput(s_TerminalInputTestCallback);
+
+    Log::Comment(L"Sending the various Ctrl+Num keys.");
+
+    unsigned int uiKeystate = LEFT_CTRL_PRESSED;
+    BYTE vkey = static_cast<WORD>('1');
+    s_pwszInputExpected = L"1";
+    TestKey(pInput, uiKeystate, vkey);
+
+    Log::Comment(NoThrowString().Format(
+        L"Skipping Ctrl+2, since that's supposed to send NUL, and doesn't play "
+        L"nicely with this test. Ctrl+2 is covered by other tests in this class."));
+
+    vkey = static_cast<WORD>('3');
+    s_pwszInputExpected = L"\x1b";
+    TestKey(pInput, uiKeystate, vkey);
+
+    vkey = static_cast<WORD>('4');
+    s_pwszInputExpected = L"\x1c";
+    TestKey(pInput, uiKeystate, vkey);
+
+    vkey = static_cast<WORD>('5');
+    s_pwszInputExpected = L"\x1d";
+    TestKey(pInput, uiKeystate, vkey);
+
+    vkey = static_cast<WORD>('6');
+    s_pwszInputExpected = L"\x1e";
+    TestKey(pInput, uiKeystate, vkey);
+
+    vkey = static_cast<WORD>('7');
+    s_pwszInputExpected = L"\x1f";
+    TestKey(pInput, uiKeystate, vkey);
+
+    vkey = static_cast<WORD>('8');
+    s_pwszInputExpected = L"\x7f";
+    TestKey(pInput, uiKeystate, vkey);
+
+    vkey = static_cast<WORD>('9');
+    s_pwszInputExpected = L"9";
+    TestKey(pInput, uiKeystate, vkey);
+}

src/terminal/input/terminalInput.cpp

@@ -185,13 +185,31 @@ static constexpr std::array<TermKeyMap, 22> s_modifierKeyMapping{
 // These sequences are not later updated to encode the modifier state in the
 //      sequence itself, they are just weird exceptional cases to the general
 //      rules above.
-static constexpr std::array<TermKeyMap, 6> s_simpleModifiedKeyMapping{
+static constexpr std::array<TermKeyMap, 14> s_simpleModifiedKeyMapping{
     TermKeyMap{ VK_BACK, CTRL_PRESSED, L"\x8" },
     TermKeyMap{ VK_BACK, ALT_PRESSED, L"\x1b\x7f" },
     TermKeyMap{ VK_BACK, CTRL_PRESSED | ALT_PRESSED, L"\x1b\x8" },
     TermKeyMap{ VK_TAB, CTRL_PRESSED, L"\t" },
     TermKeyMap{ VK_TAB, SHIFT_PRESSED, L"\x1b[Z" },
     TermKeyMap{ VK_DIVIDE, CTRL_PRESSED, L"\x1F" },
+
+    // GH#3507 - We should also be encoding Ctrl+# according to the following table:
+    // https://vt100.net/docs/vt220-rm/table3-5.html
+    // * 1 and 9 do not send any special characters, but they _should_ send
+    //   through the character unmodified.
+    // * 0 doesn't seem to send even an unmodified '0' through.
+    // * Ctrl+2 is already special-cased below in `HandleKey`, so it's not
+    //   included here.
+    TermKeyMap{ static_cast<WORD>('1'), CTRL_PRESSED, L"1" },
+    // TermKeyMap{ static_cast<WORD>('2'), CTRL_PRESSED, L"\x00" },
+    TermKeyMap{ static_cast<WORD>('3'), CTRL_PRESSED, L"\x1B" },
+    TermKeyMap{ static_cast<WORD>('4'), CTRL_PRESSED, L"\x1C" },
+    TermKeyMap{ static_cast<WORD>('5'), CTRL_PRESSED, L"\x1D" },
+    TermKeyMap{ static_cast<WORD>('6'), CTRL_PRESSED, L"\x1E" },
+    TermKeyMap{ static_cast<WORD>('7'), CTRL_PRESSED, L"\x1F" },
+    TermKeyMap{ static_cast<WORD>('8'), CTRL_PRESSED, L"\x7F" },
+    TermKeyMap{ static_cast<WORD>('9'), CTRL_PRESSED, L"9" },
+
     // These two are not implemented here, because they are system keys.
     // TermKeyMap{ VK_TAB, ALT_PRESSED, L""}, This is the Windows system shortcut for switching windows.
     // TermKeyMap{ VK_ESCAPE, ALT_PRESSED, L""}, This is another Windows system shortcut for switching windows.