Add Navbar shape for Liquid

[MikeAlhayek]

Fix #15148

[MikeAlhayek]

@sebastienros with this change, I am expecting to be able to add the following in a Layout.liquid file

{% assign navbarShape = Navbar | shape_render %}

Then later in the same file, I want to print out the rendered shape like this

{{ navbarShape }}

However, this is not working as expected. Any idea why Navbar is not rendering using Liquid?

[MikeAlhayek]

If I add use filter it works but I should not have to use filter.

Here is how it works using filters. First I register the temporary filter services.AddLiquidFilter<NavbarShapeFilter>("navbar_new");.
Then in the Layout.liquid I add {% assign navbarShape = "" | navbar_new | shape_render %} then render it later using
{{ navbarShape }}

@sebastienros @lahma

Beside the following, what else do I need to do so that Liquid recognize Navbar as a value that us constructed using the callback?

 services.Configure<TemplateOptions>(o =>
 {
     o.Scope.SetValue(nameof(Navbar), new ObjectValue(new NavbarAccessor()));
     o.MemberAccessStrategy.Register<NavbarAccessor, FluidValue>(async (obj, name, ctx) =>
     {
         if (ctx is LiquidTemplateContext context)
         {
             var displayManager = context.Services.GetRequiredService<IDisplayManager<Navbar>>();
             var updateModelAccessor = context.Services.GetRequiredService<IUpdateModelAccessor>();

             var shape = await displayManager.BuildDisplayAsync(updateModelAccessor.ModelUpdater);

             return FluidValue.Create(shape, ctx.Options);
         }

         return NilValue.Instance;
     });

     o.MemberAccessStrategy.Register<Navbar, FluidValue>((navbar, name, context) =>
     {
         return name switch
         {
             nameof(Navbar.Properties) => new ObjectValue(navbar.Properties),
             _ => NilValue.Instance
         };
     });
 });

[sebastienros]

I think it's not possible right now, because there is no way to evaluate a FluidValue (Navbar) lazily and asynchronously. It's possible to evaluate it lazily by creating a custom FluidValue whose ToObjectValue() will return something on demand, but in your case you want it to be a shape that is built asynchronously.

Only property accessors are asynchronous (ValueTask<FluidValue> GetValueAsync(string name, TemplateContext context)) which are used by the Register method. So doing Navbar.Something | filter can be asynchonous, but not Navbar | filter.

An alternative could be to create a custom Function and register it like this:

o.Scope.SetValue(nameof(Navbar), new FunctionValue((args, context) => 
{
   if (ctx is LiquidTemplateContext context)
   {
       var displayManager = context.Services.GetRequiredService<IDisplayManager<Navbar>>();
       var updateModelAccessor = context.Services.GetRequiredService<IUpdateModelAccessor>();

       var shape = await displayManager.BuildDisplayAsync(updateModelAccessor.ModelUpdater);

       return FluidValue.Create(shape, ctx.Options);
   }

   return NilValue.Instance;
}));

And then use it this way:

{{ Navbar() }}

NB: It could even take arguments