Add basic support for the DECRQSS settings query (#11152)

This PR adds support for the `DECRQSS` (Request Selection or Setting)
escape sequence, which is a standard VT query for reporting the state of
various control functions. This initial implementation only supports
queries for the `DECSTBM` margins, and the `SGR` graphic rendition
attributes.

This can be useful for certain forms of capability detection (#1040). As
one example in particular, it can serve as an alternative to the
`COLORTERM` environment variable for detecting truecolor support
(#11057). 

Of the settings that can be queried by `DECRQSS`, the only other one
that we could be supporting at the moment is `DECSCUSR` (Cursor Style).
However, that would require passing the query through to the conpty
client, which is a lot more complicated, so I thought it best to leave
for a future PR.

For now this gets the basic framework in place, so we are at least
responding to queries, and even just supporting the `SGR` attributes
query is useful in itself.

Validation
----------
I've added a unit test verifying the reports for the `DECSTBM` and `SGR`
settings with a range of different parameters. I've also tested the
`DECSTBM` and `SGR` reports manually in _Vttest_, under menu 11.2.5.3.6
(Status-String Reports).

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

@@ -536,6 +536,7 @@ DECRC
 DECREQTPARM
 DECRLM
 DECRQM
+DECRQSS
 DECRST
 DECSASD
 DECSC

src/terminal/adapter/ITermDispatch.hpp

@@ -141,6 +141,8 @@ class Microsoft::Console::VirtualTerminal::ITermDispatch
                                        const DispatchTypes::DrcsFontUsage fontUsage,
                                        const VTParameter cellHeight,
                                        const DispatchTypes::DrcsCharsetSize charsetSize) = 0; // DECDLD
+
+    virtual StringHandler RequestSetting() = 0; // DECRQSS
 };
 inline Microsoft::Console::VirtualTerminal::ITermDispatch::~ITermDispatch() {}
 #pragma warning(pop)

src/terminal/adapter/adaptDispatch.cpp

@@ -2527,6 +2527,152 @@ ITermDispatch::StringHandler AdaptDispatch::DownloadDRCS(const size_t fontNumber
     };
 }
 
+// Method Description:
+// - DECRQSS - Requests the state of a VT setting. The value being queried is
+//   identified by the intermediate and final characters of its control
+//   sequence, which are passed to the string handler.
+// Arguments:
+// - None
+// Return Value:
+// - a function to receive the VTID of the setting being queried
+ITermDispatch::StringHandler AdaptDispatch::RequestSetting()
+{
+    // We use a VTIDBuilder to parse the characters in the control string into
+    // an ID which represents the setting being queried. If the given ID isn't
+    // supported, we respond with an error sequence: DCS 0 $ r ST. Note that
+    // this is the opposite of what is documented in most DEC manuals, which
+    // say that 0 is for a valid response, and 1 is for an error. The correct
+    // interpretation is documented in the DEC STD 070 reference.
+    const auto idBuilder = std::make_shared<VTIDBuilder>();
+    return [=](const auto ch) {
+        if (ch >= '\x40' && ch <= '\x7e')
+        {
+            const auto id = idBuilder->Finalize(ch);
+            switch (id)
+            {
+            case VTID('m'):
+                _ReportSGRSetting();
+                break;
+            case VTID('r'):
+                _ReportDECSTBMSetting();
+                break;
+            default:
+                _WriteResponse(L"\033P0$r\033\\");
+                break;
+            }
+            return false;
+        }
+        else
+        {
+            if (ch >= '\x20' && ch <= '\x2f')
+            {
+                idBuilder->AddIntermediate(ch);
+            }
+            return true;
+        }
+    };
+}
+
+// Method Description:
+// - Reports the current SGR attributes in response to a DECRQSS query.
+// Arguments:
+// - None
+// Return Value:
+// - None
+void AdaptDispatch::_ReportSGRSetting() const
+{
+    // A valid response always starts with DCS 1 $ r.
+    // Then the '0' parameter is to reset the SGR attributes to the defaults.
+    std::wstring response = L"\033P1$r0";
+
+    TextAttribute attr;
+    if (_pConApi->PrivateGetTextAttributes(attr))
+    {
+        // For each boolean attribute that is set, we add the appropriate
+        // parameter value to the response string.
+        const auto addAttribute = [&](const auto parameter, const auto enabled) {
+            if (enabled)
+            {
+                response += parameter;
+            }
+        };
+        addAttribute(L";1", attr.IsBold());
+        addAttribute(L";2", attr.IsFaint());
+        addAttribute(L";3", attr.IsItalic());
+        addAttribute(L";4", attr.IsUnderlined());
+        addAttribute(L";5", attr.IsBlinking());
+        addAttribute(L";7", attr.IsReverseVideo());
+        addAttribute(L";8", attr.IsInvisible());
+        addAttribute(L";9", attr.IsCrossedOut());
+        addAttribute(L";21", attr.IsDoublyUnderlined());
+        addAttribute(L";53", attr.IsOverlined());
+
+        // We also need to add the appropriate color encoding parameters for
+        // both the foreground and background colors.
+        const auto addColor = [&](const auto base, const auto color) {
+            const auto iterator = std::back_insert_iterator(response);
+            if (color.IsIndex16())
+            {
+                const auto index = XtermToWindowsIndex(color.GetIndex());
+                const auto colorParameter = base + (index >= 8 ? 60 : 0) + (index % 8);
+                fmt::format_to(iterator, FMT_STRING(L";{}"), colorParameter);
+            }
+            else if (color.IsIndex256())
+            {
+                const auto index = Xterm256ToWindowsIndex(color.GetIndex());
+                fmt::format_to(iterator, FMT_STRING(L";{};5;{}"), base + 8, index);
+            }
+            else if (color.IsRgb())
+            {
+                const auto r = GetRValue(color.GetRGB());
+                const auto g = GetGValue(color.GetRGB());
+                const auto b = GetBValue(color.GetRGB());
+                fmt::format_to(iterator, FMT_STRING(L";{};2;{};{};{}"), base + 8, r, g, b);
+            }
+        };
+        addColor(30, attr.GetForeground());
+        addColor(40, attr.GetBackground());
+    }
+
+    // The 'm' indicates this is an SGR response, and ST ends the sequence.
+    response += L"m\033\\";
+    _WriteResponse(response);
+}
+
+// Method Description:
+// - Reports the DECSTBM margin range in response to a DECRQSS query.
+// Arguments:
+// - None
+// Return Value:
+// - None
+void AdaptDispatch::_ReportDECSTBMSetting() const
+{
+    // A valid response always starts with DCS 1 $ r.
+    std::wstring response = L"\033P1$r";
+
+    CONSOLE_SCREEN_BUFFER_INFOEX csbiex = { 0 };
+    csbiex.cbSize = sizeof(CONSOLE_SCREEN_BUFFER_INFOEX);
+    if (_pConApi->GetConsoleScreenBufferInfoEx(csbiex))
+    {
+        auto marginTop = _scrollMargins.Top + 1;
+        auto marginBottom = _scrollMargins.Bottom + 1;
+        // If the margin top is greater than or equal to the bottom, then the
+        // margins aren't actually set, so we need to return the full height
+        // of the window for the margin range.
+        if (marginTop >= marginBottom)
+        {
+            marginTop = 1;
+            marginBottom = csbiex.srWindow.Bottom - csbiex.srWindow.Top;
+        }
+        const auto iterator = std::back_insert_iterator(response);
+        fmt::format_to(iterator, FMT_STRING(L"{};{}"), marginTop, marginBottom);
+    }
+
+    // The 'r' indicates this is an DECSTBM response, and ST ends the sequence.
+    response += L"r\033\\";
+    _WriteResponse(response);
+}
+
 // Routine Description:
 // - Determines whether we should pass any sequence that manipulates
 //   TerminalInput's input generator through the PTY. It encapsulates

src/terminal/adapter/adaptDispatch.hpp

@@ -140,6 +140,8 @@ namespace Microsoft::Console::VirtualTerminal
                                    const VTParameter cellHeight,
                                    const DispatchTypes::DrcsCharsetSize charsetSize) override; // DECDLD
 
+        StringHandler RequestSetting() override; // DECRQSS
+
     private:
         enum class ScrollDirection
         {
@@ -189,6 +191,9 @@ namespace Microsoft::Console::VirtualTerminal
         void _ResetTabStops() noexcept;
         void _InitTabStopsForWidth(const size_t width);
 
+        void _ReportSGRSetting() const;
+        void _ReportDECSTBMSetting() const;
+
         bool _ShouldPassThroughInputModeChange() const;
 
         std::vector<bool> _tabStopColumns;

src/terminal/adapter/termDispatch.hpp

@@ -132,4 +132,6 @@ class Microsoft::Console::VirtualTerminal::TermDispatch : public Microsoft::Cons
                                const DispatchTypes::DrcsFontUsage /*fontUsage*/,
                                const VTParameter /*cellHeight*/,
                                const DispatchTypes::DrcsCharsetSize /*charsetSize*/) noexcept override { return nullptr; }
+
+    StringHandler RequestSetting() noexcept override { return nullptr; }; // DECRQSS
 };

src/terminal/adapter/ut_adapter/adapterTest.cpp

@@ -1990,6 +1990,109 @@ class AdapterTest
         VERIFY_IS_FALSE(_pDispatch.get()->RequestTerminalParameters(DispatchTypes::ReportingPermission::Unsolicited));
     }
 
+    TEST_METHOD(RequestSettingsTests)
+    {
+        const auto requestSetting = [=](const std::wstring_view settingId = {}) {
+            const auto stringHandler = _pDispatch.get()->RequestSetting();
+            for (auto ch : settingId)
+            {
+                stringHandler(ch);
+            }
+            stringHandler(L'\033'); // String terminator
+        };
+
+        Log::Comment(L"Requesting DECSTBM margins (5 to 10).");
+        _testGetSet->PrepData();
+        _pDispatch.get()->SetTopBottomScrollingMargins(5, 10);
+        requestSetting(L"r");
+        _testGetSet->ValidateInputEvent(L"\033P1$r5;10r\033\\");
+
+        Log::Comment(L"Requesting DECSTBM margins (full screen).");
+        _testGetSet->PrepData();
+        // Set screen height to 25 - this will be the expected margin range.
+        _testGetSet->_viewport.Bottom = _testGetSet->_viewport.Top + 25;
+        _pDispatch.get()->SetTopBottomScrollingMargins(0, 0);
+        requestSetting(L"r");
+        _testGetSet->ValidateInputEvent(L"\033P1$r1;25r\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (default).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (bold, underlined, reversed).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetBold(true);
+        _testGetSet->_attribute.SetUnderlined(true);
+        _testGetSet->_attribute.SetReverseVideo(true);
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;1;4;7m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (faint, blinking, invisible).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetFaint(true);
+        _testGetSet->_attribute.SetBlinking(true);
+        _testGetSet->_attribute.SetInvisible(true);
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;2;5;8m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (italic, crossed-out).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetItalic(true);
+        _testGetSet->_attribute.SetCrossedOut(true);
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;3;9m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (doubly underlined, overlined).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetDoublyUnderlined(true);
+        _testGetSet->_attribute.SetOverlined(true);
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;21;53m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (standard colors).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetIndexedForeground((BYTE)::XtermToWindowsIndex(3));
+        _testGetSet->_attribute.SetIndexedBackground((BYTE)::XtermToWindowsIndex(6));
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;33;46m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (AIX colors).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetIndexedForeground((BYTE)::XtermToWindowsIndex(14));
+        _testGetSet->_attribute.SetIndexedBackground((BYTE)::XtermToWindowsIndex(11));
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;96;103m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (ITU indexed colors).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetIndexedForeground256(123);
+        _testGetSet->_attribute.SetIndexedBackground256(45);
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;38;5;123;48;5;45m\033\\");
+
+        Log::Comment(L"Requesting SGR attributes (ITU RGB colors).");
+        _testGetSet->PrepData();
+        _testGetSet->_attribute = {};
+        _testGetSet->_attribute.SetForeground(RGB(12, 34, 56));
+        _testGetSet->_attribute.SetBackground(RGB(65, 43, 21));
+        requestSetting(L"m");
+        _testGetSet->ValidateInputEvent(L"\033P1$r0;38;2;12;34;56;48;2;65;43;21m\033\\");
+
+        Log::Comment(L"Requesting an unsupported setting.");
+        _testGetSet->PrepData();
+        requestSetting(L"x");
+        _testGetSet->ValidateInputEvent(L"\033P0$r\033\\");
+    }
+
     TEST_METHOD(CursorKeysModeTest)
     {
         Log::Comment(L"Starting test...");

src/terminal/parser/OutputStateMachineEngine.cpp

@@ -661,6 +661,9 @@ IStateMachineEngine::StringHandler OutputStateMachineEngine::ActionDcsDispatch(c
                                           parameters.at(6),
                                           parameters.at(7));
         break;
+    case DcsActionCodes::DECRQSS_RequestSetting:
+        handler = _dispatch->RequestSetting();
+        break;
     default:
         handler = nullptr;
         break;

src/terminal/parser/OutputStateMachineEngine.hpp

@@ -147,6 +147,7 @@ namespace Microsoft::Console::VirtualTerminal
         enum DcsActionCodes : uint64_t
         {
             DECDLD_DownloadDRCS = VTID("{"),
+            DECRQSS_RequestSetting = VTID("$q")
         };
 
         enum Vt52ActionCodes : uint64_t