Segfault from collecting a range of duals

[ChrisRackauckas]

MWE:

using ForwardDiff
function f(p)
    sum(collect(0.0:p[1]:p[2]))
end
ForwardDiff.gradient(f, [0.2,25.0])

[KristofferC]

Always good to check with segfaults:

> julia -q --check-bounds=yes

julia> using ForwardDiff

julia> function f(p)
           sum(collect(0.0:p[1]:p[2]))
       end
f (generic function with 1 method)

julia> ForwardDiff.gradient(f, [0.2,25.0])
ERROR: BoundsError: attempt to access 124-element Vector{ForwardDiff.Dual{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2}} at index [125]
Stacktrace:
 [1] setindex!
   @ ./array.jl:839 [inlined]
 [2] vcat(rs::StepRange{ForwardDiff.Dual{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2}, ForwardDiff.Dual{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2}})
   @ Base ./range.jl:1036
 [3] collect
   @ ./range.jl:1043 [inlined]
 [4] f(p::Vector{ForwardDiff.Dual{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2}})
   @ Main ./REPL[1]:2
 [5] vector_mode_dual_eval
   @ ~/.julia/packages/ForwardDiff/5gUap/src/apiutils.jl:37 [inlined]
 [6] vector_mode_gradient(f::typeof(f), x::Vector{Float64}, cfg::ForwardDiff.GradientConfig{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2, Vector{ForwardDiff.Dual{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2}}})
   @ ForwardDiff ~/.julia/packages/ForwardDiff/5gUap/src/gradient.jl:106
 [7] gradient(f::Function, x::Vector{Float64}, cfg::ForwardDiff.GradientConfig{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2, Vector{ForwardDiff.Dual{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2}}}, ::Val{true})
   @ ForwardDiff ~/.julia/packages/ForwardDiff/5gUap/src/gradient.jl:19
 [8] gradient(f::Function, x::Vector{Float64}, cfg::ForwardDiff.GradientConfig{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2, Vector{ForwardDiff.Dual{ForwardDiff.Tag{typeof(f), Float64}, Float64, 2}}}) (repeats 2 times)
   @ ForwardDiff ~/.julia/packages/ForwardDiff/5gUap/src/gradient.jl:17
 [9] top-level scope
   @ REPL[2]:1

[KristofferC]

julia> p = [0.2, 25.0];

julia> (r = 0.0:p[1]:p[2]) |> length
126

julia> pd = Dual.(p);

julia> (rd = 0.0:pd[1]:pd[2]) |> length
124

julia> last(r)
25.0

julia> last(rd)
Dual{Nothing}(24.8)

julia> Base.steprange_last(0.0, 0.2, 25.0)
ERROR: ArgumentError: StepRange should not be used with floating point
Stacktrace:
 [1] steprange_last(start::Float64, step::Float64, stop::Float64)
   @ Base ./range.jl:215
 [2] top-level scope
   @ REPL[4]:1

julia> Base.steprange_last(Dual(0.0), Dual(0.2), Dual(25.0))
Dual{Nothing}(24.8)

[KristofferC]

#549