False ambiguity with Union

[timholy]

julia> module A
       foo{T<:Union{Int,Int64}}(x::AbstractUnitRange{T}) = 1
       foo{T<:Union{UInt,UInt64}}(x::AbstractUnitRange{T}) = 2
       end
A

julia> Base.Test.detect_ambiguities(A)
1-element Array{Tuple{Method,Method},1}:
 (foo{T<:Int64}(x::AbstractUnitRange{T}) in A at REPL[10]:2,foo{T<:UInt64}(x::AbstractUnitRange{T}) in A at REPL[10]:3)

[timholy]

xref #19998

[yuyichao]

I think this is why we want a version of ambiguity detection that ignores Union{}?

[Keno]

Yes

[timholy]

Assuming the goal is to restore the ambiguity tests before 0.6 is out, it's going to be necessary to fix this, so I added a milestone label.

[timholy]

Hmm, it looks like this was fixed in e101000, though it's not the default. Presumably we should either make it the default or change

julia/test/ambiguous.jl

Line 137 in 0e970f0

@test_broken detect_ambiguities(Core, Base; imported=true) == []

to include allow_bottom=false?

EDIT: oh, I see, the fix is only partial.