Add support for DECSCUSR "0" to restore cursor to user default (#7379)

This PR is about the behavior of DECSCUSR. This PR changes the meaning
of DECSCUSR 0 to restore the cursor style back to user default. This
differs from what VT spec says but it’s used in popular terminal
emulators like iTerm2 and VTE-based ones. See #1604. 

Another change is that for parameter greater than 6, DECSCUSR should be
ignored, instead of restoring the cursor to legacy. This PR fixes it.
See #7382.

Fixes #1604.

src/cascadia/TerminalCore/Terminal.cpp

@@ -134,6 +134,8 @@ void Terminal::UpdateSettings(ICoreSettings settings)
                                       cursorShape);
     }
 
+    _defaultCursorShape = cursorShape;
+
     for (int i = 0; i < 16; i++)
     {
         _colorTable.at(i) = settings.GetColorTableEntry(i);

src/cascadia/TerminalCore/Terminal.hpp

@@ -221,6 +221,7 @@ private:
     std::array<COLORREF, XTERM_COLOR_TABLE_SIZE> _colorTable;
     COLORREF _defaultFg;
     COLORREF _defaultBg;
+    CursorType _defaultCursorShape;
     bool _screenReversed;
 
     bool _snapOnInput;

src/cascadia/TerminalCore/TerminalApi.cpp

@@ -389,8 +389,10 @@ bool Terminal::SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle) noex
 
     switch (cursorStyle)
     {
-    case DispatchTypes::CursorStyle::BlinkingBlockDefault:
-        [[fallthrough]];
+    case DispatchTypes::CursorStyle::UserDefault:
+        finalCursorType = _defaultCursorShape;
+        shouldBlink = true;
+        break;
     case DispatchTypes::CursorStyle::BlinkingBlock:
         finalCursorType = CursorType::FullBox;
         shouldBlink = true;
@@ -415,9 +417,10 @@ bool Terminal::SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle) noex
         finalCursorType = CursorType::VerticalBar;
         shouldBlink = false;
         break;
+
     default:
-        finalCursorType = CursorType::Legacy;
-        shouldBlink = false;
+        // Invalid argument should be ignored.
+        return true;
     }
 
     _buffer->GetCursor().SetType(finalCursorType);

src/host/outputStream.cpp

@@ -513,6 +513,19 @@ bool ConhostInternalGetSet::PrivateEraseAll()
     return SUCCEEDED(DoSrvPrivateEraseAll(_io.GetActiveOutputBuffer()));
 }
 
+// Method Description:
+// - Retrieves the current user default cursor style.
+// Arguments:
+// - style - Structure to receive cursor style.
+// Return Value:
+// - true if successful. false otherwise.
+bool ConhostInternalGetSet::GetUserDefaultCursorStyle(CursorType& style)
+{
+    const auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
+    style = gci.GetCursorType();
+    return true;
+}
+
 // Routine Description:
 // - Connects the SetCursorStyle call directly into our Driver Message servicing call inside Conhost.exe
 //   SetCursorStyle is an internal-only "API" call that the vt commands can execute,

src/host/outputStream.hpp

@@ -107,6 +107,7 @@ public:
     bool PrivatePrependConsoleInput(std::deque<std::unique_ptr<IInputEvent>>& events,
                                     size_t& eventsWritten) override;
 
+    bool GetUserDefaultCursorStyle(CursorType& style) override;
     bool SetCursorStyle(CursorType const style) override;
     bool SetCursorColor(COLORREF const color) override;
 

src/terminal/adapter/DispatchTypes.hpp

@@ -216,8 +216,8 @@ namespace Microsoft::Console::VirtualTerminal::DispatchTypes
 
     enum class CursorStyle : unsigned int
     {
-        BlinkingBlock = 0,
-        BlinkingBlockDefault = 1,
+        UserDefault = 0, // Implemented as "restore cursor to user default".
+        BlinkingBlock = 1,
         SteadyBlock = 2,
         BlinkingUnderline = 3,
         SteadyUnderline = 4,

src/terminal/adapter/adaptDispatch.cpp

@@ -2160,8 +2160,11 @@ bool AdaptDispatch::SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle)
 
     switch (cursorStyle)
     {
+    case DispatchTypes::CursorStyle::UserDefault:
+        _pConApi->GetUserDefaultCursorStyle(actualType);
+        fEnableBlinking = true;
+        break;
     case DispatchTypes::CursorStyle::BlinkingBlock:
-    case DispatchTypes::CursorStyle::BlinkingBlockDefault:
         fEnableBlinking = true;
         actualType = CursorType::FullBox;
         break;
@@ -2187,6 +2190,10 @@ bool AdaptDispatch::SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle)
         fEnableBlinking = false;
         actualType = CursorType::VerticalBar;
         break;
+
+    default:
+        // Invalid argument should be handled by the connected terminal.
+        return false;
     }
 
     bool success = _pConApi->SetCursorStyle(actualType);

src/terminal/adapter/conGetSet.hpp

@@ -70,6 +70,7 @@ namespace Microsoft::Console::VirtualTerminal
         virtual bool PrivateEnableAnyEventMouseMode(const bool enabled) = 0;
         virtual bool PrivateEnableAlternateScroll(const bool enabled) = 0;
         virtual bool PrivateEraseAll() = 0;
+        virtual bool GetUserDefaultCursorStyle(CursorType& style) = 0;
         virtual bool SetCursorStyle(const CursorType style) = 0;
         virtual bool SetCursorColor(const COLORREF color) = 0;
         virtual bool PrivatePrependConsoleInput(std::deque<std::unique_ptr<IInputEvent>>& events,

src/terminal/adapter/ut_adapter/adapterTest.cpp

@@ -434,6 +434,12 @@ public:
         return TRUE;
     }
 
+    bool GetUserDefaultCursorStyle(CursorType& style) override
+    {
+        style = CursorType::Legacy;
+        return true;
+    }
+
     bool SetCursorStyle(const CursorType cursorType) override
     {
         Log::Comment(L"SetCursorStyle MOCK called...");

src/terminal/parser/OutputStateMachineEngine.hpp

@@ -239,7 +239,7 @@ namespace Microsoft::Console::VirtualTerminal
         bool _GetOscSetColor(const std::wstring_view string,
                              DWORD& rgb) const noexcept;
 
-        static constexpr DispatchTypes::CursorStyle DefaultCursorStyle = DispatchTypes::CursorStyle::BlinkingBlockDefault;
+        static constexpr DispatchTypes::CursorStyle DefaultCursorStyle = DispatchTypes::CursorStyle::UserDefault;
         bool _GetCursorStyle(const gsl::span<const size_t> parameters,
                              DispatchTypes::CursorStyle& cursorStyle) const noexcept;