Allow Attributes on Generic Type Parameters

[AdamSpeight2008]

It is possible to create an attribute (in VB) that can be used on generic parameter.

<AttributeUsage(AttributeTargets.GenericParameter)>
Public Class NumericAttribute : Inherits Attribute
    Public Sub New()
        MyBase.New()
    End Sub
End Class

Yet consuming that attribute in VB isn't permitted.

Public Structure NRange(Of <Numeric>Tx, Sx)
End Structure

produces the following errors on <

Identifier expected.
'As', comma or ')' expected.

We should remedy the issue, and allow them.

---

Currently syntax node TypeParameterSyntax doesn't support them (in C# in does), so will need to extend the definition. Or define another that inherits from TypeParameterSyntax.
Parsing should be relatively simple as parsing attributes is already implement, so adding an additional parsing step to parsing of a generic parameters should not be to hard.

[ghost]

This would be very powerful!

[AnthonyDGreen]

Just looks like an oversight that it was never supported.

[AnthonyDGreen]

Update: The 12/6/2017 LDM approved this idea in principle.

[AdamSpeight2008]

Was there a preferred implementation?

• Change the layout of TypeSyntax to unify against C#'s
• Inherit from TypeSyntax

[AnthonyDGreen]

An implementation should change TypeParameterSyntax to add the attribute list in the front as C# does. And this new capability should apply to type parameters of generic types and generic methods.

[AdamSpeight2008]

@KathleenDollard and @AnthonyDGreen
Prototyped in this branch: VB_AttributesOnGenericTypeParameters

Note: Isn't protected via a Feature Flag