Html.RenderPartialAsync("") shows an error in editor

[DamianEdwards]

Using VS2017 d15prerel (15.3 26423.1-Preview)

Add the following to a Razor file:

@section Scripts {
    @{ await Html.RenderPartialAsync("_ValidationScriptsPartial"); }
}

You get a squigglie indicating the overload doesn't exist:

You can however "Go to definition" on the method and it finds it OK. Also, runtime works fine.

[DamianEdwards]

@NTaylorMullen @rynowak

[NTaylorMullen]

Super odd.... That extension methods exists in the same namespace as the base RenderPartialAsync method. I'll have to try it out once my VS updates.

[rynowak]

@NTaylorMullen - the error is on RenderAsyncDelegate in the generated code

[NTaylorMullen]

@NTaylorMullen - the error is on RenderAsyncDelegate in the generated code

Ooo i see. Ya gotta fix this guy.

[rynowak]

Can you figure out what the safe fix is for this for preview 1?

[NTaylorMullen]

Issue here is that our code generation is compatible with 1.0.0 Mvc but not 2.0.0 Mvc.

We render:

DefineSection("Foo", async (__razor_section_writer) => {
});

Which works in 1.0.0. However, in 2.0.0 our define section method looks like this:

public virtual void DefineSection(string name, RenderAsyncDelegate section)

Where RenderAsyncDelegate is:

public delegate Task RenderAsyncDelegate();

The most minimal fix for this for preview1 would be to create an overload to DefineSection in RazorPage.cs that took in a Func<object, Task> as its second parameter instead of RenderAsyncDelegate. If not, we'll have to tackle code gen based on version.

What do you guys think?

[DamianEdwards]

I'd vote for the minimal fix for preview1.

[rynowak]

I'd vote for the minimal fix for preview1.

This guy right here.

Is this a pages-specific issue or do we need to fix this for pages and views?

[NTaylorMullen]

Is this a pages-specific issue or do we need to fix this for pages and views?

Pages and Views

[rynowak]

So if I understand correctly, the fix here is to add a dummy public virtual void DefineSection(string name, Func<TextWriter, Text> section) to RazorPageBase. (Probably with [EditorBrowsableNever])

This will be targeted by the design time codegen, but will have no purpose at runtime.

[NTaylorMullen]

So if I understand correctly, the fix here is to add a dummy public virtual void DefineSection(string name, Func<TextWriter, Text> section) to RazorPageBase. (Probably with [EditorBrowsableNever])

This will be targeted by the design time codegen, but will have no purpose at runtime.

Exactly.

[NTaylorMullen]

IF we really wanted we could have the runtime impl do other stuff:

1. throw
2. call through to the primary DefineSection impl
3. Noop

[NTaylorMullen]

Went with option 2

[NTaylorMullen]

aspnet/Mvc@490f94d
aspnet/Mvc@e8c102a

[rynowak]

👍 🔥 🥈