Error on syntactically valid conditional with `is`

[maurobringolf]

Input:

public class ClassName {
    public void M() { 
        var x = y is y ? [] : z ?? [];
    }
}

Output:

error CS1513: } expected

Expected behavior:

formats without error

---

When replacing is with == it works fine.

[PetSerAl]

Is it syntactically valid? It seems that C# compiler want to parse ? in y ? [] as part of nullable type name (meaning y is array of y?), not as part of ternary operator. Writing it like this var x = (y is y) ? [] : z ?? []; or var x = y is (y) ? [] : z ?? []; make it syntactically valid. I presume Csharpier just use Roslyn to parse files, that means it exactly the same errors as C# compiler.

[PetSerAl]

It seems there are differences in how different compiler version parse that:

class C
{
    void M(object o)
    {
        int[]? a = o is int ? [] : null;
    }
}

That compiles in SDK 9.0.300 and 10.0.100-preview.4.25258.110, but on sharplab.io it fails with compile error.

[belav]

Looks like updating Microsoft.CodeAnalysis.CSharp allows csharpier to correctly parse that c#