Error involving SIGNATURES and UnionAll type arguments

[tkoolen]

Thanks for the great package!

I found an annoying issue on 0.6 related to UnionAll types. If you use SIGNATURES as follows:

using DocStringExtensions
"""
$(SIGNATURES)
"""
function f(::Type{T}) where {T}
    T
end

then ?f results in

ERROR: type UnionAll has no field parameters
Stacktrace:
 [1] to_tuple_type(::Any) at ./reflection.jl:468
 [2] methods(::Any, ::Any) at ./reflection.jl:583
 [3] getmethods!(::Array{Method,1}, ::Function, ::Type{T} where T) at /home/twan/code/RigidBodyDynamics/v0.6/DocStringExtensions/src/utilities.jl:86
 [4] #methodgroups#3(::Bool, ::Function, ::Function, ::Type{T} where T, ::Module) at /home/twan/code/RigidBodyDynamics/v0.6/DocStringExtensions/src/utilities.jl:24
 [5] format(::DocStringExtensions.MethodSignatures, ::Base.AbstractIOBuffer{Array{UInt8,1}}, ::Base.Docs.DocStr) at /home/twan/code/RigidBodyDynamics/v0.6/DocStringExtensions/src/abbreviations.jl:290
 [6] formatdoc(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::Base.Docs.DocStr, ::DocStringExtensions.MethodSignatures) at /home/twan/code/RigidBodyDynamics/v0.6/DocStringExtensions/src/abbreviations.jl:25
 [7] formatdoc(::Base.Docs.DocStr) at ./docs/Docs.jl:178
 [8] parsedoc(::Base.Docs.DocStr) at ./docs/Docs.jl:186
 [9] _collect(::Array{Base.Docs.DocStr,1}, ::Base.Generator{Array{Base.Docs.DocStr,1},Base.Docs.#parsedoc}, ::Base.EltypeUnknown, ::Base.HasShape) at ./array.jl:454
 [10] doc(::Base.Docs.Binding, ::Type{T} where T) at ./docs/Docs.jl:312
 [11] doc(::Base.Docs.Binding) at ./docs/Docs.jl:280

This is because the sig passed into getmethods! is Union{Tuple{Type{T}}, Tuple{T}} where T, which is a UnionAll, not a Union.

[tkoolen]

Ref: JuliaLang/julia#20872.