Fix wide char support for WriteConsoleOutputAttribute (#18796)

When we overwrite the attributes during the fill,
we must retain the lead/trail byte attributes.

Closes #18746

## Validation Steps Performed
* Added a unit test ✅

src/host/_output.cpp

@@ -110,15 +110,25 @@ static FillConsoleResult FillConsoleImpl(SCREEN_INFORMATION& screenInfo, FillCon
             switch (mode)
             {
             case FillConsoleMode::WriteAttribute:
+            {
                 for (; columns < columnsAvailable && inputPos < lengthToWrite; ++columns, ++inputPos)
                 {
-                    infoBuffer[columns].Attributes = input[inputPos];
+                    // Overwrite all attributes except for the lead/trail byte markers.
+                    // Those are used by WriteConsoleOutputWImplHelper to correctly serialize the input.
+                    constexpr auto LT = COMMON_LVB_LEADING_BYTE | COMMON_LVB_TRAILING_BYTE;
+                    auto& attributes = infoBuffer[columns].Attributes;
+                    attributes = (input[inputPos] & ~LT) | (attributes & LT);
                 }
                 break;
+            }
             case FillConsoleMode::FillAttribute:
                 for (const auto attr = input[0]; columns < columnsAvailable && inputPos < lengthToWrite; ++columns, ++inputPos)
                 {
-                    infoBuffer[columns].Attributes = attr;
+                    // Overwrite all attributes except for the lead/trail byte markers.
+                    // Those are used by WriteConsoleOutputWImplHelper to correctly serialize the input.
+                    constexpr auto LT = COMMON_LVB_LEADING_BYTE | COMMON_LVB_TRAILING_BYTE;
+                    auto& attributes = infoBuffer[columns].Attributes;
+                    attributes = (attr & ~LT) | (attributes & LT);
                 }
                 break;
             case FillConsoleMode::WriteCharacter:

src/host/ut_host/VtIoTests.cpp

@@ -52,6 +52,16 @@ static constexpr std::wstring_view s_initialContentVT{
     // clang-format on
 };
 
+static constexpr std::wstring_view s_initialContentVTWide{
+    // clang-format off
+    L""
+    sgr_red("〇") sgr_blu("一") sgr_red("二") sgr_blu("三") "\r\n"
+    sgr_red("四") sgr_blu("五") sgr_red("六") sgr_blu("七") "\r\n"
+    sgr_blu("八") sgr_red("九") sgr_blu("十") sgr_red("百") "\r\n"
+    sgr_blu("千") sgr_red("万") sgr_blu("億") sgr_red("兆")
+    // clang-format on
+};
+
 class ::Microsoft::Console::VirtualTerminal::VtIoTests
 {
     BEGIN_TEST_CLASS(VtIoTests)
@@ -71,11 +81,11 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         return { &rxBuf[0], read };
     }
 
-    void setupInitialContents() const
+    void setupInitialContents(bool wide) const
     {
         auto& sm = screenInfo->GetStateMachine();
         sm.ProcessString(L"\033c");
-        sm.ProcessString(s_initialContentVT);
+        sm.ProcessString(wide ? s_initialContentVTWide : s_initialContentVT);
         sm.ProcessString(L"\x1b[H" sgr_rst());
     }
 
@@ -277,7 +287,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
 
     TEST_METHOD(WriteConsoleOutputAttribute)
     {
-        setupInitialContents();
+        setupInitialContents(false);
 
         static constexpr std::array payload{ red, blu, red, blu };
         static constexpr til::point target{ 6, 1 };
@@ -295,7 +305,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
 
     TEST_METHOD(WriteConsoleOutputCharacterW)
     {
-        setupInitialContents();
+        setupInitialContents(false);
 
         size_t written = 0;
         std::string_view expected;
@@ -354,7 +364,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         actual = readOutput();
         VERIFY_ARE_EQUAL(expected, actual);
 
-        setupInitialContents();
+        setupInitialContents(false);
 
         // Writing at the start of a line.
         THROW_IF_FAILED(routines.FillConsoleOutputAttributeImpl(*screenInfo, red, 3, { 0, 0 }, cellsModified, false));
@@ -388,6 +398,25 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         VERIFY_ARE_EQUAL(expected, actual);
     }
 
+    TEST_METHOD(FillConsoleOutputAttributeWide)
+    {
+        setupInitialContents(true);
+
+        size_t cellsModified = 0;
+        std::string_view expected;
+        std::string_view actual;
+
+        // Writing nothing should produce nothing.
+        THROW_IF_FAILED(routines.FillConsoleOutputAttributeImpl(*screenInfo, red, 4, { 2, 1 }, cellsModified, false));
+        expected =
+            decsc() //
+            cup(2, 3) sgr_red("五六") //
+            decrc();
+        actual = readOutput();
+        VERIFY_ARE_EQUAL(4u, cellsModified);
+        VERIFY_ARE_EQUAL(expected, actual);
+    }
+
     TEST_METHOD(FillConsoleOutputCharacterW)
     {
         size_t cellsModified = 0;
@@ -407,7 +436,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         actual = readOutput();
         VERIFY_ARE_EQUAL(expected, actual);
 
-        setupInitialContents();
+        setupInitialContents(false);
 
         // Writing at the start of a line.
         THROW_IF_FAILED(routines.FillConsoleOutputCharacterWImpl(*screenInfo, L'a', 3, { 0, 0 }, cellsModified, false));
@@ -453,7 +482,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         std::string_view expected;
         std::string_view actual;
 
-        setupInitialContents();
+        setupInitialContents(false);
 
         // Scrolling from nowhere to somewhere are no-ops and should not emit anything.
         THROW_IF_FAILED(routines.ScrollConsoleScreenBufferWImpl(*screenInfo, { 0, 0, -1, -1 }, {}, std::nullopt, L' ', 0, false));
@@ -487,7 +516,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         //
         //   m   n   M   N   o   p   O   P
         //
-        setupInitialContents();
+        setupInitialContents(false);
 
         // Scrolling from somewhere to somewhere.
         //
@@ -626,7 +655,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         std::string_view expected;
         std::string_view actual;
 
-        setupInitialContents();
+        setupInitialContents(false);
 
         // Scrolling from nowhere to somewhere are no-ops and should not emit anything.
         THROW_IF_FAILED(routines.ScrollConsoleScreenBufferWImpl(*screenInfo, { 0, 0, -1, -1 }, {}, std::nullopt, L' ', 0, false));
@@ -660,7 +689,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
         //
         //   m   n   M   N   o   p   O   P
         //
-        setupInitialContents();
+        setupInitialContents(false);
 
         // Scrolling from somewhere to somewhere.
         //
@@ -797,7 +826,7 @@ class ::Microsoft::Console::VirtualTerminal::VtIoTests
             &screenInfoAlt));
 
         routines.SetConsoleActiveScreenBufferImpl(*screenInfoAlt);
-        setupInitialContents();
+        setupInitialContents(false);
         THROW_IF_FAILED(routines.SetConsoleOutputModeImpl(*screenInfoAlt, ENABLE_PROCESSED_OUTPUT | ENABLE_WRAP_AT_EOL_OUTPUT | ENABLE_VIRTUAL_TERMINAL_PROCESSING));
         readOutput();