Fix isdone for empty product iterators, fixes #43921 (#43947)

* Fix the issue #43921 * add a test Co-authored-by: Kristoffer <kcarlsson89@gmail.com> (cherry picked from commit b8a77da)
JuliaLang · Dec 14, 2022 · 44b24dd · 44b24dd
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commit 44b24dd
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diff --git a/base/iterators.jl b/base/iterators.jl
@@ -1041,6 +1041,7 @@ iterate(::ProductIterator{Tuple{}}, state) = nothing
     done1 === true || return done1 # false or missing
     return _pisdone(tail(iters), tail(states)) # check tail
 end
+@inline isdone(::ProductIterator{Tuple{}}, states) = true
 @inline isdone(P::ProductIterator, states) = _pisdone(P.iterators, states)
 
 @inline _piterate() = ()

diff --git a/test/iterators.jl b/test/iterators.jl
@@ -902,3 +902,11 @@ end
     @test last(Iterators.map(identity, 1:3)) == 3
     @test last(Iterators.filter(iseven, (Iterators.map(identity, 1:3)))) == 2
 end
+
+@testset "empty product iterators" begin
+    v = nothing
+    for (z,) in zip(Iterators.product())
+        v = z
+    end
+    @test v == ()
+end