cumsum for Ones has inconsistent output type depending on element type

[mtfishman]

For example using FillArrays v1.9.3:

julia> using FillArrays

julia> cumsum(Ones{Int64}(4))
Base.OneTo(4)

julia> cumsum(Ones{Int32}(4))
4-element Vector{Int32}:
 1
 2
 3
 4

I believe the issue is this line: https://github.com/JuliaArrays/FillArrays.jl/blob/v1.9.3/src/FillArrays.jl#L578.

It may in fact be an issue with convert of Base.OneTo:

julia> convert(AbstractVector{Int64}, Base.OneTo(4))
Base.OneTo(4)

julia> convert(AbstractVector{Int32}, Base.OneTo(4))
4-element Vector{Int32}:
 1
 2
 3
 4

i.e. it seems like it should preserve that it is Base.OneTo and just change the element type. A workaround could be to use:

cumsum(x::AbstractOnesVector{II}) where II<:Integer = convert(AbstractVector{II}, oneto(II(length(x))))

[mtfishman]

I raised an issue here: JuliaLang/julia#53806

[dlfivefifty]

Using this might be a work around: https://github.com/putianyi889/EltypeExtensions.jl

cf #352

[jishnub]

On a longer term, I think JuliaLang/julia#48894 should fix many of these issues. I'll try to push that.