Vararg constructor is bad news for compiling big types (regression vs 0.5)

[SimonDanisch]

Julia 0.6 rc3:

module VisualizeTypes
abstract type Composable end
(::Type{T}){T <: Composable, N}(c::Vararg{Pair, N}) = T(c) # Remove the varar
type Window{T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18} <: Composable
    Area::T1
    Open::T2
    EnteredWindow::T3
    Focused::T4
    MouseInside::T5
    MouseButtons::T6
    MousePosition::T7
    MouseScroll::T8
    MouseDrag::T9
    KeyboardButtons::T10
    KeyboardUnicode::T11
    DroppedFiles::T12
    NativeWindow::T13
    Camera::T14
    Renderlist::T15
    Scene::T16
    Color::T17
    Light::T18
end

end 

This module takes ~40s to compile. Remove the Vararg and change it to anything else will make the compilation time go down to 0.4s.

[vtjnash]

Reducible to:

julia> @time typeintersect(Tuple{Vararg{Pair}}, Tuple{T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18} where {T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18})
  4.325776 seconds (7.08 M allocations: 2.250 GiB, 1.44% gc time)
Tuple{T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18} where {T1<:Pair, T2<:Pair, T3<:Pair, T4<:Pair, T5<:Pair, T6<:Pair, T7<:Pair, T8<:Pair, T9<:Pair, T10<:Pair, T11<:Pair, T12<:Pair, T13<:Pair, T14<:Pair, T15<:Pair, T16<:Pair, T17<:Pair, T18<:Pair}

Would be interesting to know if there is a simple fix here, but not sure it would be a general performance improvement. Just avoid adding constraints to your function parameters and life will quite often be good or at least better.