Cannot backprop `x^a` when `x` is negative about diffrules.jl HOT 2 CLOSED

julia> Tracker.gradient((x,p) -> x^p, -2.0, 2)
ERROR: DomainError with -2.0:
log will only return a complex result if called with a complex argument. Try log(Complex(x)).

julia> Zygote.gradient((x,p) -> x^p, -2.0, 2)
(-4.0, 0.0)

julia> ForwardDiff.gradient(((x,p),) -> x^p, [-2.0, 2])
ERROR: DomainError with -2.0:
log will only return a complex result if called with a complex argument. Try log(Complex(x)).

julia> Tracker.gradient((x) -> x^2, -2.0)
(-4.0 (tracked),)

julia> Zygote.gradient((x) -> x^2, -2.0)
(-4.0,)

julia> ForwardDiff.derivative((x) -> x^2, -2.0)
-4.0