Cursor shape gets reverted to legacy style after hiding the cursor and then making it visible again in console window

[daxian-dbw]

Environment

Windows build number: Microsoft Windows [Version 10.0.18363.535]
Windows Terminal version (if applicable): NA

Any other software? No

Steps to reproduce

After setting the cursor shape in Properties->Terminal, hiding and then showing the cursor by setting Console.CursorVisible to false and then true causes the cursor shape to be restored to the legacy style in console host.

The following simple C# program can show the problem:

using System;
using System.Text;

namespace cursorShape
{
    class Program
    {
        static void Main(string[] args)
        {
            const string prompt = "PROMP> ";
            StringBuilder sb = new StringBuilder();
            int top = Console.CursorTop;

            Console.OutputEncoding = Encoding.UTF8;
            Console.Write(prompt);

            while (true)
            {
                var key = Console.ReadKey();
                if (key.Key == ConsoleKey.Q)
                {
                    break;
                }

                sb.Append(key.KeyChar);

                Console.CursorVisible = false;   // Hide the cursor before rewriting
                Console.SetCursorPosition(0, top);
                Console.Write($"{prompt}{sb}");
                Console.SetCursorPosition(Console.CursorLeft, top);
                Console.CursorVisible = true;    // Show the cursor afterwards
            }
        }
    }
}

Expected behavior

Setting Console.CursorVisible should not revert the cursor shape.

Actual behavior

The cursor shape gets reverted from Solid Box to the legacy style (Underline):

Related issues

#409 and #1145 and PowerShell/PSReadLine#903
Those 2 issues were reported in the PowerShell+PSReadLine context. PSReadLine depends on Console.CursorVisible to hide and show the cursor during rendering, so the cursor shape gets reverted.

[DHowett-MSFT]

Well, heck.

[j4james]

As explained in #409, the problem is that calling the SetConsoleCursorInfo sets the cursor size, and setting the cursor size forces the cursor shape back to the legacy style (because that's the only shape for which the size is applicable AFAIK).

It's easy enough to "fix". We could just delete this line from the SetCursorInformation method:

terminal/src/host/screenInfo.cpp

Line 1778 in 6f667f4

cursor.SetType(CursorType::Legacy);

But that's a change in behavior for a public API, and it's possible some applications could actually be relying on that behavior (although I would think that unlikely).

Ideally the Console.CursorVisible property should be using an API that just sets the visibility and nothing else, but but I don't think there is such a thing. The best you could do is use a VT sequence, but that's obviously not going to work with older versions of Windows.