Bug (?) in MPolyFactor when coefficients are are not in a field

[fingolfin]

julia> R,(x,y) = ZZ[:x,:y]
(Multivariate polynomial ring in 2 variables over integers, AbstractAlgebra.Generic.MPoly{BigInt}[x, y])

julia> f = AbstractAlgebra.MPolyFactor.mfactor_char_zero((2*x+x)^2)
9 * x^2

Looking at the code, I think what effectively happens is that f.unit is set to the content of the polynomial. But really that should also be factorized.

So in this case I'd expect an error to be thrown because we don't implement factor for BigInt.

One can now quibble whether this is a bug, after all AbstractAlgebra.MPolyFactor.mfactor_char_zero is not factor and could just declare that it doesn't handle factorization in the coefficient ring. In that interpretation, it simply alllows itself to abuse the unit field of type Fac to store a non-unit.