Fix type stability in multiset_permutations

Author: FedericoStra

src/permutations.jl

@@ -287,7 +287,7 @@ julia> collect(multiset_permutations([1,1,2], 3))
 """
 function multiset_permutations(a, t::Integer)
     m = unique(collect(a))
-    f = [sum([c == x for c in a]) for x in m]
+    f = [sum(c == x for c in a)::Int for x in m]
     multiset_permutations(m, f, t)
 end
 

test/permutations.jl

@@ -71,6 +71,7 @@ end
     # derangements
     @test length(collect(derangements(1:4))) == 9
     @test length(collect(derangements(1:8))) == derangement(8) == 14833
+    @test collect(derangements([])) == [[]]
     @test collect(derangements(Int[])) == [Int[]]
     @test collect(derangements([1])) == Vector{Int}[]
     @test collect(derangements([1, 1])) == Vector{Int}[]