New JSImport / JSExport attribute support

[linkdotnet]

I am creating a discussion before creating a useless issue, because I am not 100% sure about the stuff I will write in a second.

To give a bit context, I will talk about the following API Proposal: JavaScript interop with [JSImport] and [JSExport] attributes and Roslyn

In its current state it will be public with .net7.0.

The idea is to use Roslyn to create importable or exportable JS-Interop functions.

The simple example:

// here we bind to well known console.log on the blobal JS namespace
[JSImport("console.log")]
// there is no return value marshaling, but exception would be marshaled
internal static partial void Log(
    // this one will marshal C# string to JavaScript native string by value (with some optimizations)
    string message);

Will give an easy way of having a strongly types C# function which calls JS-code.
This scenario is right now not supported by bUnit. Or at least I don't see how. As I understand this function this will be widely used as it makes interop trivial in a lot of scenarios. At the moment this is limited to wasm.

If that makes sense to you @egil I will transform this into a reasonable feature request :D

EDIT: This is also the reason our nightly build is failing as the "old" way got flagged obsolete: #788

[egil]

FFS did they forget about testing again?

Is this not using IJSRuntime under the hood? If yes, then things just works. If this is a new interop API entirely then, yeah.

[linkdotnet]

Only had a short look, but it looks like the latter:

public static partial class JavaScript
{
    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Interop.JavaScript.JSImportGenerator", "7.0.6.36704")]
    internal static partial void Log(string message)
    {
        if (__signature_Log_271308160 == null)
        {
            __signature_Log_271308160 = global::System.Runtime.InteropServices.JavaScript.JSFunctionBinding.BindJSFunction("console.log", null, new global::System.Runtime.InteropServices.JavaScript.JSMarshalerType[]{global::System.Runtime.InteropServices.JavaScript.JSMarshalerType.Discard, global::System.Runtime.InteropServices.JavaScript.JSMarshalerType.String});
        }

        global::System.Span<global::System.Runtime.InteropServices.JavaScript.JSMarshalerArgument> __arguments_buffer = stackalloc global::System.Runtime.InteropServices.JavaScript.JSMarshalerArgument[3];
        ref global::System.Runtime.InteropServices.JavaScript.JSMarshalerArgument __arg_exception = ref __arguments_buffer[0];
        __arg_exception.Initialize();
        ref global::System.Runtime.InteropServices.JavaScript.JSMarshalerArgument __arg_return = ref __arguments_buffer[1];
        __arg_return.Initialize();
        // Setup - Perform required setup.
        ref global::System.Runtime.InteropServices.JavaScript.JSMarshalerArgument __message_native__js_arg = ref __arguments_buffer[2];
        __message_native__js_arg.ToJS(message);
        global::System.Runtime.InteropServices.JavaScript.JSFunctionBinding.InvokeJS(__signature_Log_271308160, __arguments_buffer);
    }

    [global::System.ThreadStaticAttribute]
    static global::System.Runtime.InteropServices.JavaScript.JSFunctionBinding __signature_Log_271308160;
}

This is the result of the console.log example above. Dissambling InvokeJS will just show me this:

[Versioning.SupportedOSPlatformAttribute("browser")]
[CLSCompliant(false)]
[System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
public sealed class JSFunctionBinding
{
    public static void InvokeJS(JSFunctionBinding signature, Span<JSMarshalerArgument> arguments) { throw new System.PlatformNotSupportedException(System.SR.SystemRuntimeInteropServicesJavaScript_PlatformNotSupported);  }
    public static JSFunctionBinding BindJSFunction(string functionName, string moduleName, ReadOnlySpan<JSMarshalerType> signatures) { throw new System.PlatformNotSupportedException(System.SR.SystemRuntimeInteropServicesJavaScript_PlatformNotSupported);  }
    public static JSFunctionBinding BindManagedFunction(string fullyQualifiedName, int signatureHash, ReadOnlySpan<JSMarshalerType> signatures) { throw new System.PlatformNotSupportedException(System.SR.SystemRuntimeInteropServicesJavaScript_PlatformNotSupported);  }
}

Which might be really not implemented at the moment, see here (you have to go to JSFunctionBinding.cs).

So let's keep an eye on it.

[egil]

I asked about the testability of this in the original proposal. Let's see what they respond with.

[egil]

Ok some input. It's basically not something we need to deal with, see dotnet/runtime#70133 (comment).

What we should do is add a section to the docs where we tell users they should not use JSImport directly in their components but in a test controllable type.

[linkdotnet]

Perfect. To be fair I stumbled over this in the pre-release notes... so kind of not officially communicated and therefore unsure what the plan of the dotnet team was or is.