Mono (C#) Tuple support

[jasonswearingen]

Godot version:
v3.2-beta4_mono_win64

OS/device including version:
Win10 (PC) using VSCode

Issue description:

Mono 6.x is supposed to support the C# 7.0 Tuple types, but it doesn't work. VSCode shows errors and trying to run the scene in Godot also errors with identical error messages.

When I try to paste in the example from https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7#tuples

(string Alpha, string Beta) namedLetters = ("a", "b");
Console.WriteLine($"{namedLetters.Alpha}, {namedLetters.Beta}");

VSCode outputs errors:

{
	"resource": "/c:/repos/godot/projects/Godot basic Move and Dodge Game CSharp/scripts/Steve.cs",
	"owner": "csharp",
	"code": "CS8137",
	"severity": 8,
	"message": "Cannot define a class or member that utilizes tuples because the compiler required type 'System.Runtime.CompilerServices.TupleElementNamesAttribute' cannot be found. Are you missing a reference? [Godot basic Move and Dodge Game CSharp]",
	"source": "csharp",
	"startLineNumber": 29,
	"startColumn": 3,
	"endLineNumber": 29,
	"endColumn": 30
}

//and
{
	"resource": "/c:/repos/godot/projects/Godot basic Move and Dodge Game CSharp/scripts/Steve.cs",
	"owner": "csharp",
	"code": "CS8179",
	"severity": 8,
	"message": "Predefined type 'System.ValueTuple`2' is not defined or imported [Godot basic Move and Dodge Game CSharp]",
	"source": "csharp",
	"startLineNumber": 29,
	"startColumn": 3,
	"endLineNumber": 29,
	"endColumn": 30
}

I looked in my Godot_v3.2-beta4_mono_win64\GodotSharp\Mono\lib\mono\4.5 folder and don't see a System.Runtime.CompilerServices.dll so maybe that's it? (though there is System.Runtime.CompilerServices.Unsafe.dll)

I'm sorry but I'm new to Godot and Mono so not sure if this is something I could workaround on my end (install my own version of Mono?) or if there is another problem.

I tried installing the System.ValueTuple Nuget package (another error mentioned) but that didn't help.

Steps to reproduce:

	public override void _Ready()
	{
		(string Alpha, string Beta) namedLetters = ("a", "b");
		Console.WriteLine($"{namedLetters.Alpha}, {namedLetters.Beta}");
}

Minimal reproduction project:

if you need a project, let me know, but as it's more regarding Mono+VSCode+Project I think that wouldn't help much.

[jasonswearingen]

Did some more research but I'm at a loss. However this comment by Mr Zagaeski [MSFT] might be helpful: https://developercommunity.visualstudio.com/solutions/121139/view.html

[jasonswearingen]

I got it working. it turns out I didn't follow the steps to install nuget packages properly.

What I did (That did not work) was:

1. Using VSCode's Nuget Package Manager Extension I added "System.ValueTuple" v4.5
2. from command prompt I ran dotnet restore (the extension recommended I do this to install the nuget package)
3. Adjust the <Version> tag as per: Adding a nuget package makes Godot not build #30970 (comment)

The problem is, dotnet restore seems to change the .csproj in some way that corrupts it for mono use. after doing this I couldn't get it building again (either in VSCode or Godot) so something about this is incompatable with Mono it seems. (I have a feeling it's something like CRLF or BOM tweaking)

This workflow WORKED:

1. Using VSCode's Nuget Package Manager Extension I added "System.ValueTuple" v4.5
2. downloaded the nuget.exe from it's website and ran nuget restore (which is NOT what VSCode suggests you do!)
3. Adjust the <Version> tag as per: Adding a nuget package makes Godot not build #30970 (comment)

Doing that, now Tuples are working in my project:

	public override void _Ready()
	{
		var tuple = (first: "hello", second: "godot!!!");
		var (third, fourth) = ("goodbye", "godot");
		GD.Print($"{tuple.first}, {tuple.second} .... {third} {fourth}");
	}

So maybe you can add some documentation telling people not to use dotnet restore (and the <Version> workaround) to this doc page? https://docs.godotengine.org/en/latest/getting_started/scripting/c_sharp/c_sharp_basics.html#using-nuget-packages-in-godot

EDIT: I submitted a pull request to update these docs.

[jasonswearingen]

admins: feel free to close this, just please consider mentioning the proper workflow in docs (see the last paragraph of my last comment)

Edit: (I submitted a pull request, as linked below)