Fix a promote issue for AbsMSeries over Poly tower (#2061)

Author: lgoettgens

src/generic/AbsMSeries.jl

@@ -670,6 +670,10 @@ end
 #
 ###############################################################################
 
+function (R::AbsMSeriesRing)(x::RingElement)
+  return R(base_ring(R)(x))
+end
+
 function (R::AbsMSeriesRing{T, S})(x::S, prec::Vector{Int}) where
                           {T <: RingElement, S <: AbstractAlgebra.MPolyRingElem{T}}
     for v in prec

src/generic/AbsSeries.jl

@@ -307,7 +307,7 @@ end
 #
 ###############################################################################
 
-function (a::AbsPowerSeriesRing{T} where T <: RingElement)(b::RingElement)
+function (a::AbsPowerSeriesRing)(b::RingElement)
    return a(base_ring(a)(b))
 end
 

test/generic/AbsMSeries-test.jl

@@ -642,3 +642,10 @@ end
       @test evaluate(f, [y], [h]) == evaluate(f, [x, h])
    end
 end
+
+@testset "Generic.AbsMSeries.#2060" begin
+   R, a = polynomial_ring(QQ, :a)
+   F, x = polynomial_ring(R, :x)
+   S, (eps,) = power_series_ring(F, 4, [:ϵ])
+   @test coefficients(eps + a) == [a, 1]
+end