Add coercion to QQ for all number fields (thofma#1152)

.github/workflows/CILong.yml

@@ -43,7 +43,7 @@ jobs:
         uses: julia-actions/cache@v1
       - name: "Build package"
         uses: julia-actions/julia-buildpkg@latest
-      - run: julia --color=yes --project -e 'using Pkg; Pkg.add(PackageSpec(name="GAP")); Pkg.add(PackageSpec(name="Polymake"));'
+      - run: julia --color=yes --project -e 'using Pkg; Pkg.add(PackageSpec(name="Polymake")); Pkg.add(PackageSpec(name="GAP"));'
         #- run: julia --color=yes --project -e 'using Pkg; Pkg.add(PackageSpec(name="Polymake"));'
       - name: "Run long tests"
         uses: julia-actions/julia-runtest@latest

Project.toml

@@ -1,6 +1,6 @@
 name = "Hecke"
 uuid = "3e1990a7-5d81-5526-99ce-9ba3ff248f21"
-version = "0.18.15"
+version = "0.18.16"
 
 [deps]
 AbstractAlgebra = "c3fe647b-3220-5bb0-a1ea-a7954cac585d"

src/NumField/NfAbs/NfAbs.jl

@@ -1320,5 +1320,5 @@ function force_coerce_cyclo(a::AnticNumberField, b::nf_elem, throw_error::Type{V
 end
 
 (::QQField)(a::nf_elem) = (is_rational(a) && return coeff(a, 0)) || error("not a rational")
-(::ZZRing)(a::nf_elem) = (isinteger(a) && return numerator(coeff(a, 0))) || error("not an integer")
 
+(::ZZRing)(a::nf_elem) = (is_integer(a) && return numerator(coeff(a, 0))) || error("not an integer")

src/NumField/NfAbs/NonSimple.jl

@@ -1238,3 +1238,14 @@ end
 function Base.hash(a::NfAbsNSElem, h::UInt)
   return Base.hash(a.data, h)
 end
+
+################################################################################
+#
+#  Coercion
+#
+################################################################################
+
+function (K::QQField)(a::NfAbsNSElem)
+  @req is_constant(a.data) "Element must be rational"
+  return constant_coefficient(a.data)
+end

src/NumField/NfRel/NfRel.jl

@@ -483,6 +483,12 @@ function in(a::NfRelElem{nf_elem}, K::AnticNumberField)
   return true
 end
 
+function (K::QQField)(a::NfRelElem)
+  for i in 2:degree(parent(a))
+    @req iszero(coeff(a, i - 1)) "Element must be rational"
+  end
+  return QQ(coeff(a, 0))
+end
 
 ################################################################################
 #

src/NumField/NfRel/NfRelNS.jl

@@ -838,3 +838,14 @@ end
 
 absolute_discriminant(K::NfRelNS) = discriminant(K, FlintQQ)
 
+################################################################################
+#
+#  Coercion
+#
+################################################################################
+
+function (K::QQField)(a::NfRelNSElem)
+  d = data(a)
+  @req is_constant(d) "Element must be rational"
+  return QQ(constant_coefficient(d))
+end

test/NfAbs/NonSimple.jl

@@ -170,4 +170,10 @@
     @test is_isomorphic(L, K)
   end
 
+  @testset "coercion" begin
+    Qx, x = FlintQQ["x"]
+    K, (a, b) = number_field([x^2 - 2, x^3 - 3])
+    @test (@inferred QQ(2*a^0)) == 2*one(QQ)
+    @test_throws ArgumentError QQ(a)
+  end
 end

test/NfRel/NfRel.jl

@@ -110,4 +110,15 @@
       @test chip == sum([x^i for i=0:p-1])
     end
   end
+
+  @testset "coercion" begin
+    K, a = Hecke.rationals_as_number_field()
+    Kt, t = K["t"]
+    L, b = number_field(t - 1, "b")
+    Lt, t = L["t"]
+    M, o = number_field(t^3 + 2, "o")
+    @test QQ(2*b^0) == 2*one(QQ)
+    @test QQ(2*o^0) == 2*one(QQ)
+    @test_throws ArgumentError QQ(o)
+  end
 end

test/NfRel/NonSimple.jl

@@ -16,5 +16,9 @@
     @test string(a) isa String
   end
 
-
+  @testset "coercion" begin
+    @test QQ(2*a^0) == 2*one(QQ)
+    @test_throws ArgumentError QQ(a)
+    @test_throws ErrorException QQ(gen(K) * a^0)
+  end
 end