`StreamReader` over standard input stream does not echo if `Console.ReadLine` has been run first

[mjcheetham]

Description

When targeting .NET Core 3.x (netcoreapp3.0 and netcoreapp3.1), a call to StreamReader::ReadLine with the standard input Stream as the underlying stream does not 'echo' typed characters at the terminal on macOS/Linux IF a call to Console.ReadLine has been made before.

This issue does not occur when targetting netcoreapp2.1; both Console.ReadLine and StreamReader::ReadLine echo typed characters.

using System;
using System.IO;

class Program
{
    // Only repros in .NET Core 3.1
    static void Main(string[] args)
    {
        // Comment this line out and echo with StreamReader:ReadLine works
        string consoleText = Console.ReadLine();

        var stdin = Console.OpenStandardInput();
        using (var sr = new StreamReader(stdin))
        {
            // Does not echo if the Console.ReadLine call has been executed
            string readerText = sr.ReadLine();
        }
    }
}

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <!-- Does not repro if you target .NET Core 2.1 -->
    <!--<TargetFramework>netcoreapp2.1</TargetFramework>-->
  </PropertyGroup>
</Project>

$ dotnet run
hello<return>                               # Console.ReadLine
<typed characters here do not echo><return> # StreamReader.ReadLine
<program exit>

Configuration

OSs

• Ubuntu 20.04 LTS x86_64
• macOS 10.15 Catalina x86_64

Target Frameworks

• netcoreapp3.0
• netcoreapp3.1

Installed SDK
3.1.301

Regression?

Yes. When targeting .NET Core 2.1 this does not repro.

Other information

I know there have been many issues in this space over in prior releases in order to support ReadKey(intercept: true) on *nix systems. I imagine there's a problem in the initialisation of the console and terminal options for echo since this only happens if you interact with the console and standard input stream via Console.ReadLine before.

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[stephentoub]

cc: @tmds

[mjcheetham]

You can also replace the Console.ReadLine with a ReadKey to get the same results.

[tmds]

This is caused by dotnet/corefx#35621.
Currently echoing is only turned back on when a child process needs it.
ReadKey writes to Console to make the input echo.
We can do something similar for OpenStandardInput Stream.

@stephentoub you can assign this to me.

[stephentoub]

thanks, Tom.