Remove ListDirectoryAsync(string path, CancellationToken cancellationToken)

[drieseng]

@IgorMilavec added a ListDirectoryAsync(string path, CancellationToken cancellationToken) to SftpClient that returns a Task<IEnumerable.

I don't want to ship a release (even if it's beta) with this method.
I see two options:

• Remove this method
• Change return type to IAsyncEnumerable<ISftpFile>

Let's discuss these (and perhaps other) options in the next days.

[WojciechNagorski]

We have a PR for second opinion but there are problems. Tomorrow I will look at it.
#907

[WojciechNagorski]

To use IAsyncEnumerable on .NET 4.6.2 and .NET Standard 2.0 we can add a reference to Microsoft's Nuget Microsoft.Bcl.AsyncInterfaces. This package is not required starting with .NET Standard 2.1, .NET Core 3.0 (and higher).

The possible solution:

<PropertyGroup>
    <TargetFrameworks>net462;netstandard2.0;net6.0</TargetFrameworks>
    <!-- It is important to use C# 8.0 -->
    <LangVersion>8.0</LangVersion> 
</PropertyGroup>

<ItemGroup Condition="'$(TargetFramework)'=='net462' or '$(TargetFramework)'=='netstandard2.0' ">
    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="7.0.0" />
</ItemGroup>

To be honest, I don't like the solution from PR #907. IMO we should choose one of the following options:

1. Expose IAsyncEnumerable version of the ListDirectoryAsync method using the Microsoft.Bcl.AsyncInterfaces Nuget. There is only one problem. IAsyncEnumerable requires C# 8.0 which is not officially supported in .NET 4.6.2 and .NET Standard 2.0. So users will have to set <LangVersion>8.0</LangVersion> if they want to use ListDirectoryAsync method. There is more information: https://stackoverflow.com/a/57020770/4809321
2. Add support for .NET Standard 2.1 and expose IAsyncEnumerable version of the ListDirectoryAsync method only for .NET 6 and .NET Standard 2.1. For older .NET 4.6.2 and .NET Standard 2.0 just remove this method.

The more I think about it, the more I'm in favor of option 2.

[drieseng]

@WojciechNagorski, I also favor the second option.