"tuple must be non-empty" when iterating two nested `Iterators.product`

[fjarri]

The code:

using Base.Iterators: product
println(collect(product(product())))

Expected:

(ProductIterator{Tuple{}}(()),)

(or something of that sort, in the real code I have

iters = product(product(...))
for x in iters
    for y in x
        ...
    end
end

)

Got:

ERROR: LoadError: ArgumentError: tuple must be non-empty
Stacktrace:
 [1] first(::Tuple{}) at ./tuple.jl:74
 [2] _pisdone at ./iterators.jl:803 [inlined]
 [3] isdone at ./iterators.jl:810 [inlined]
 [4] _pisdone at ./iterators.jl:804 [inlined]
 [5] isdone at ./iterators.jl:810 [inlined]
 [6] iterate at ./iterators.jl:842 [inlined]
 [7] copyto!(::Array{Tuple{Tuple{}},0}, ::Base.Iterators.ProductIterator{Tuple{Base.Iterators.ProductIterator{Tuple{}}}}) at ./abstractarray.jl:650
 [8] _collect(::UnitRange{Int64}, ::Base.Iterators.ProductIterator{Tuple{Base.Iterators.ProductIterator{Tuple{}}}}, ::Base.HasEltype, ::Base.HasShape{0}) at ./array.jl:563
 [9] collect(::Base.Iterators.ProductIterator{Tuple{Base.Iterators.ProductIterator{Tuple{}}}}) at ./array.jl:557
 [10] top-level scope at none:0
 [11] include at ./boot.jl:317 [inlined]
 [12] include_relative(::Module, ::String) at ./loading.jl:1038
 [13] include(::Module, ::String) at ./sysimg.jl:29
 [14] exec_options(::Base.JLOptions) at ./client.jl:229
 [15] _start() at ./client.jl:421

versioninfo():

Julia Version 1.0.0
Commit 5d4eaca (2018-08-08 20:58 UTC)
Platform Info:
OS: macOS (x86_64-apple-darwin14.5.0)
CPU: Intel(R) Core(TM) i7-4870HQ CPU @ 2.50GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.0 (ORCJIT, haswell)

[barucden]

This issue seems to have been fixed by #43947.