Segfault with bivariate polynomial ring (promotion)

[thofma]

julia> R = ResidueRing(ZZ, 2)
Residue ring of Integer Ring modulo 2

julia> T, x = R["x"]
(Univariate Polynomial Ring in x over Residue ring of Integer Ring modulo 2,x)

julia> S, y = T["y"]
(Univariate Polynomial Ring in y over Univariate Polynomial Ring in x over Residue ring of Integer Ring modulo 2,y)

julia> zero(R)*y^0
Speicherzugriffsfehler (Speicherabzug geschrieben)

The error is a segfault, but I was too lazy to change languages.

I can reproduce it with the release and development version of julia.

It worked with an older version of Nemo, but I did not have time to do a bisect. It is probably due to the changed promotion system.

[thofma]

Here is the proper error message:

ERROR: StackOverflowError:                                                                                              
 in promote_rule(::Type{Nemo.GenRes{Nemo.fmpz}}, ::Type{Nemo.GenPoly{Nemo.nmod_poly}}) at /home/thofmann/.julia/v0.5/Nem
o/src/generic/Residue.jl:255 (repeats 80000 times)