Typechecking error with `Vararg`

[goerch]

Reported on discourse:

Julia 1.6.5

julia> const FormArgs{T, K} = Vararg{T, K}
Vararg{T, K} where {T, K}

julia> FormArgs{Int, 2}
Vararg{Int64, 2}

Julia 1.7.2

julia> const FormArgs{T, K} = Vararg{T, K}
Vararg{Any}

julia> FormArgs{Int, 2}
ERROR: ArgumentError: apply_type: too many arguments (expected 2)
Stacktrace:
 [1] top-level scope
   @ REPL[2]:1

[JeffBezanson]

Vararg is subject to some extra normalizations since it's not really a type. If you want, you can work around this by making FormArgs a function.

We might be able to fix this by only doing the normalization when the Vararg is placed inside a tuple type, but I'd have to look into it.