Fix another VT input double-encoding issue (#19083)

Closes #17264
Closes microsoft/edit#182

Long shot, but probably also...
Closes #18579
Closes #19082

Author: lhecker

src/terminal/adapter/InteractDispatch.cpp

@@ -62,15 +62,38 @@ void InteractDispatch::WriteString(const std::wstring_view string)
 {
     if (!string.empty())
     {
-        const auto codepage = _api.GetOutputCodePage();
-        InputEventQueue keyEvents;
-
-        for (const auto& wch : string)
+        const auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
+#pragma warning(suppress : 26429) // Symbol 'inputBuffer' is never tested for nullness, it can be marked as not_null (f.23).
+        const auto inputBuffer = gci.GetActiveInputBuffer();
+
+        // The input *may* be keyboard input in which case we must call CharToKeyEvents.
+        //
+        // However, it could also be legitimate VT sequences (e.g. a bracketed paste sequence).
+        // If we called `InputBuffer::Write` with those, we would end up indirectly
+        // calling `TerminalInput::HandleKey` and "double encode" the sequence.
+        // The effect of this is noticeable with the German keyboard layout, for instance,
+        // where the [ key maps to AltGr+8, and we fail to map it back to [ later.
+        //
+        // It's worth noting that all of this is bad design in either case.
+        // The way it should work is that we write INPUT_RECORDs and Strings as-is into the
+        // InputBuffer, and only during retrieval they're converted into one or the other.
+        // This prevents any kinds of double-encoding issues.
+        if (inputBuffer->IsInVirtualTerminalInputMode())
         {
-            CharToKeyEvents(wch, codepage, keyEvents);
+            inputBuffer->WriteString(string);
         }
+        else
+        {
+            const auto codepage = _api.GetOutputCodePage();
+            InputEventQueue keyEvents;
 
-        WriteInput(keyEvents);
+            for (const auto& wch : string)
+            {
+                CharToKeyEvents(wch, codepage, keyEvents);
+            }
+
+            inputBuffer->Write(keyEvents);
+        }
     }
 }