sum(f, op, a; dims) unexpectedly applies f to zero element

[martinholters]

Julia 0.6:

julia> sum(x -> x+1, [1], 1)
1-element Array{Int64,1}:
 2

Julia 0.7:

julia> sum(x -> x+1, [1], dims=1) # should give same result according to deprecation
1-element Array{Int64,1}:
 3

I think the problem is that mapreduce with a dims keyword arg applies f to the implied v0:

julia> mapreduce(x -> (println(x); x+1), +, [1], dims=1)
0
1
1-element Array{Int64,1}:
 3

Compare to

julia> mapreduce(x -> (println(x); x+1), +, [1])
1  # output from println
2  # return value