BoundsError in 2d comprehension

[andreasnoack]

From MAT.jl's test suite

julia> Any[v for _ in 1:1, v in (1.0, 2.01, "string", Any["string1" "string2"])]
ERROR: BoundsError: attempt to access 1×4 Array{Any,2} at index [5]
Stacktrace:
 [1] copy!(::Array{Any,2}, ::Base.Generator{Base.Iterators.Prod2{UnitRange{Int64},Tuple{Float64,Float64,String,Array{Any,2}}},##1#2}) at ./abstractarray.jl:499
 [2] _collect(::Type{Any}, ::Base.Generator{Base.Iterators.Prod2{UnitRange{Int64},Tuple{Float64,Float64,String,Array{Any,2}}},##1#2}, ::Base.HasShape) at ./array.jl:313
 [3] collect(::Type{Any}, ::Base.Generator{Base.Iterators.Prod2{UnitRange{Int64},Tuple{Float64,Float64,String,Array{Any,2}}},##1#2}) at ./array.jl:310

Bisection blames #18457

cc: @JeffBezanson

[yuyichao]

This seems to be caused by Base.product with a heterogeneous tuple input. It causes a infinite loop in

for x in Base.product(1:1, (1, "2"))
end

[yuyichao]

It's also important that the first iterator has a single element so probably a wrong handling of edge case there?

[yuyichao]

I think the issue is likely

julia> oftype(Nullable{Int}(), nothing)
Nullable{Int64}()

julia> oftype(Nullable{Any}(), nothing)
Nullable{Any}(nothing)

I assume using typeof(nv2)() should work?

[tkelman]

that nothing conversion method seems more dangerous than useful in terms of hitting corner cases like this. can we deprecate it?

[nalimilan]

I wouldn't deprecate it now if we expect Nullable to be replaced with Union{T, Void} soon. I think we just need a new method for convert(Nullable{Any}, ...).

[JeffBezanson]

That workaround is safe, but there's a more general specificity problem. Type{Nullable{T}}, Void used to be more specific than Type{Nullable{T}}, T, and isn't anymore. That should be fixable.

[yuyichao]

Is Type{Nullable{T}}, Void actually more specific though? It matches Type{Nullable{Int}}, Void where as the second one doesn't.

[JeffBezanson]

True, but I think for any arguments where both definitions match, the one that explicitly names Void is arguably more specific.