Enhance Console.ReadLine() to return at Tab

[iSazonov]

AB#1115512
On Windows PowerShell implements tab completions in command line (without PSReadline).
https://github.com/PowerShell/PowerShell/blob/0f7efddd22a4a44f61a2f22de86f5d6b6aa47564/src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleControl.cs#L753

On Unix PowerShell can not do this because Console API doesn't support read line complete when the Tab button is pressed.
https://github.com/dotnet/corefx/blob/a10890f4ffe0fadf090c922578ba0e606ebdd16c/src/System.Console/src/System/IO/StdInReader.cs#L149

Once feature request is implemented, in PowerShell repo we can use the same code on all systems, enhance supported features on Unix and remove explicit P/Invokes.

Feature request

Enhance Console API so that Console.ReadLine() works like Windows ReadConsole:

• can returns when the Tab (others?) button is pressed.
• accepts InitialChars such as Windows ReadConsole.

Additional

Bash benefits from Readline library https://en.wikipedia.org/wiki/GNU_Readline

[stephentoub]

Enhance Console API so that Console.ReadKey() can returns when the Tab (others?) button is pressed.

I don't understand the request. Console.ReadKey() does return a ConsoleKeyInfo for Tab when Tab is pressed. You can see it's explicitly handled here:
https://github.com/dotnet/corefx/blob/b58eb14dd8694d5142d63fde7b89e9f6a9bf32b1/src/System.Console/src/System/IO/StdInReader.cs#L232-L233
The code you linked to is the implementation of Console.ReadLine, not ReadKey.

When I run this:

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Ready...");
        while (true)
        {
            ConsoleKeyInfo k = Console.ReadKey(intercept: true);
            Console.WriteLine(k.Key + ": " + (int)k.KeyChar);
        }
    }
}

and then type a bunch of tabs, I see:

stoub@stoubdesktop:~/tmpapp$ dotnet run -c Release
Ready...
Tab: 9
Tab: 9
Tab: 9
Tab: 9
Tab: 9
Tab: 9
Tab: 9

[iSazonov]

Using search I got into the file https://github.com/dotnet/corefx/blob/c7a4807728206d959e1878242c0bd6d35948fc2d/src/System.Console/src/System/ConsolePal.Unix.cs#L91
Is it wrong?

[stephentoub]

Is it wrong?

I'm not sure what you're asking. That ReadKey method you linked to in that file calls StdinReader.ReadKey:
https://github.com/dotnet/corefx/blob/c7a4807728206d959e1878242c0bd6d35948fc2d/src/System.Console/src/System/IO/StdInReader.cs#L351
which contains the Tab handling.

[iSazonov]

@stephentoub Thanks for clarify! I really confused ReadKey and Readline methods in CoreFX repo.

[iSazonov]

I corrected my request.

[wfurt]

This seems like weird request as TAB does not constitute end of line e.g. if the function returns it would give less than line.
It seems like if handling of special keys is needed best approach would be reading keys into buffer and adding handlers for TAB or any other special keys (like '?').

[iSazonov]

@wfurt It seems you say about implementing a power line editor class which allows customizations and hooks/handlers. Looks good to me.

[eiriktsarpalis]

So it would seem like implementing a modified variant of StreamReader.ReadLine() on top of either System.Console.ReadKey() or System.Console.In might be an acceptable workaround for your use case?

Assuming you would like to see this functionality added to System.Console, I'm curious what shape you were thinking this might have? Clearly we cannot make a breaking change to Console.ReadLine(), so I suppose it would have to be a new method?

[iSazonov]

I'm curious what shape you were thinking this might have?

Ideally extensible line editor.

[Akarinnnnn]

Yes. #35063 meant this. The "TAB" in C++ STL is called "delim" so I used that name.

[jeffhandley]

We have discussed this potential feature again and concluded that we are going to close the request. Features related to tab/word completion and/or other key handling behaviors are commonly needed in shells, and that is the layer where we think the feature is best implemented. With the Unix Console.ReadKey rewrite (#72193) complete in .NET 7.0, we expect that key-level functionality should now be much more reliable to implement upstack as well. Upstack implementations would be wrappers around Console.ReadKey() loops that allow special-case handling of specific keys.

[iSazonov]

/cc @SteveL-MSFT @daxian-dbw for information. It seems we could to unify PowerShell ReadLine method.