fix aliasing bugs with add!

src/arithmetic.jl

@@ -59,10 +59,9 @@ function add!(result::GroupRingElem, X::GroupRingElem, Y::GroupRingElem)
     result === X && return addeq!(result, Y)
     result === Y && return addeq!(result, X)
 
-    result = _dealias(result, X, Y)
-    @inbounds for i in eachindex(result.coeffs)
-        result.coeffs[i] = X.coeffs[i] + Y.coeffs[i]
-    end
+    result = zero!(result)
+    # @inbounds for i in eachindex(result.coeffs)
+    result.coeffs .= X.coeffs .+ Y.coeffs
     return result
 end
 
@@ -108,7 +107,7 @@ end
 
 function +(X::GroupRingElem{T, GR}, Y::GroupRingElem{T, GR}) where {T, GR<:GroupRing}
     # @assert parent(X) == parent(Y)
-    return add!(X, X, Y)
+    return add!(zero(parent(X)), X, Y)
 end
 
 function +(X::GroupRingElem{S}, Y::GroupRingElem{T}) where {S,T}
@@ -205,7 +204,7 @@ end
 
 # divisions
 (/)(X::GroupRingElem, a) = inv(a)*X
-(//)(X::GroupRingElem, a::Union{Integer, Rational}) = inv(a)*X
+(//)(X::GroupRingElem, a::Union{Integer, Rational}) = 1//a*X
 
 ###############################################################################
 #

test/runtests.jl

@@ -3,6 +3,7 @@ using Test
 using AbstractAlgebra
 using GroupRings
 using SparseArrays
+using LinearAlgebra
 
 include("AARing_interface_conformance.jl")
 

test/unittests.jl

@@ -1,5 +1,3 @@
-using LinearAlgebra
-
 @testset "Unit tests" begin
     R = AbstractAlgebra.zz
     G = PermGroup(4)
@@ -38,7 +36,7 @@ using LinearAlgebra
         @test length(X.coeffs.nzind) < k
         @test norm(X, 4) isa Float64
 
-        @test aug(X) isa Int
+        @test aug(X) isa elem_type(base_ring(RG))
         @test supp(X) isa Vector{elem_type(G)}
         @test [RG[g] for g in supp(X)] == X.coeffs.nzind
 
@@ -90,14 +88,15 @@ using LinearAlgebra
         for (inplace_op, op) in [(AbstractAlgebra.mul!, *),
                                (AbstractAlgebra.add!, +)]
             let X = X, Y = Y
-                @test inplace_op(X, X, Y) == op(X, Y)
-                @test inplace_op(X, Y, X) == op(Y, X)
+                @test op(X, Y) == inplace_op(X, X, Y)
+                @test op(Y, X) == inplace_op(X, Y, X)
 
-                Z = inplace_op(X, X, Y)
-                @test Z == op(X, Y)
 
-                Z = inplace_op(Z, Y, X)
-                @test Z == op(Y, X)
+                Z = op(X, Y)
+                @test Z == inplace_op(Z, X, Y)
+
+                Z = op(Y, X)
+                @test Z == inplace_op(Z, Y, X)
             end
         end