Add many @req !is_trivial checks

Author: lgoettgens

docs/src/constructors.md

@@ -74,7 +74,7 @@ AbstractAlgebra.jl and explain what mathematical domains they represent.
 | $S = K((x))$ (to precision $n$)      | `S, x = laurent_series_field(K, n, :x)`               |
 | $S = R((x, y))$ (to precision $n$)   | `S, (x, y) = laurent_polynomial_ring(R, n, [:x, :y])` |
 | Puiseux series ring to precision $n$ | `S, x = puiseux_series_ring(R, n, :x)`                |
-| Puiseux series field to precision $n$| `S, x = puiseux_series_field(R, n, :x)`               |
+| Puiseux series field to precision $n$| `S, x = puiseux_series_field(K, n, :x)`               |
 | $S = K(x)(y)/(f)$                    | `S, y = function_field(f, :y)` with $f\in K(x)[t]$    |
 | $S = \mathrm{Frac}_R$                | `S = fraction_field(R)`                               |
 | $S = R/(f)$                          | `S, = residue_ring(R, f)`                              |

src/Fraction.jl

@@ -823,6 +823,7 @@ that it will always be returned by a call to the constructor when the same
 base ring $R$ is supplied.
 """
 function fraction_field(R::Ring; cached::Bool=true)
+   @req !is_trivial(R) "Zero rings are currently not supported as coefficient ring."
    return Generic.fraction_field(R; cached=cached)
 end
 

src/FreeAssociativeAlgebra.jl

@@ -270,6 +270,7 @@ function free_associative_algebra(
   s::Vector{Symbol};
   cached::Bool = true,
 )
+  @req !is_trivial(R) "Zero rings are currently not supported as coefficient ring."
   parent_obj = Generic.FreeAssociativeAlgebra{elem_type(R)}(R, s, cached)
   return (parent_obj, gens(parent_obj))
 end

src/LaurentPoly.jl

@@ -39,5 +39,7 @@ julia> rand(R, -3:3, -9:9)
 -3*x^2 - 8*x + 4 + 3*x^-1 - 6*x^-2 + 9*x^-3
 ```
 """
-laurent_polynomial_ring(R::Ring, s::VarName; cached::Bool = true) =
-   Generic.laurent_polynomial_ring(R, Symbol(s); cached)
+function laurent_polynomial_ring(R::Ring, s::VarName; cached::Bool = true)
+   @req !is_trivial(R) "Zero rings are currently not supported as coefficient ring."
+   return Generic.laurent_polynomial_ring(R, Symbol(s); cached)
+end

src/LaurentSeries.jl

@@ -24,8 +24,10 @@ object `S` will be cached so that supplying the same base ring, string and
 precision in future will return the same parent object and generator. If
 caching of the parent object is not required, `cached` can be set to `false`.
 """
-laurent_series_ring(R::Ring, prec::Int, s::VarName; cached::Bool=true) =
-   Generic.laurent_series_ring(R, prec, Symbol(s); cached)
+function laurent_series_ring(R::Ring, prec::Int, s::VarName; cached::Bool=true)
+   @req !is_trivial(R) "Zero rings are currently not supported as coefficient ring."
+   return Generic.laurent_series_ring(R, prec, Symbol(s); cached)
+end
 
 @doc raw"""
     laurent_series_field(R::Field, prec::Int, s::VarName; cached::Bool=true)

src/MPoly.jl

@@ -1508,5 +1508,7 @@ true
 Like [`polynomial_ring(R::Ring, s::Vector{Symbol})`](@ref) but return only the
 multivariate polynomial ring.
 """
-polynomial_ring_only(R::T, s::Vector{Symbol}; internal_ordering::Symbol=:lex, cached::Bool=true) where T<:Ring =
-   mpoly_ring_type(T)(R, s, internal_ordering, cached)
+function polynomial_ring_only(R::T, s::Vector{Symbol}; internal_ordering::Symbol=:lex, cached::Bool=true) where T<:Ring
+   @req !is_trivial(R) "Zero rings are currently not supported as coefficient ring."
+   return mpoly_ring_type(T)(R, s, internal_ordering, cached)
+end

src/MatRing.jl

@@ -441,5 +441,6 @@ Return parent object corresponding to the ring of $n\times n$ matrices over
 the ring $R$.
 """
 function matrix_ring(R::NCRing, n::Int)
-   Generic.matrix_ring(R, n)
+   @req !is_trivial(R) "Zero rings are currently not supported as base ring."
+   return Generic.matrix_ring(R, n)
 end

src/Matrix.jl

@@ -6633,6 +6633,7 @@ randmat_with_rank(S::MatSpace{T}, rank::Int, v...) where {T <: RingElement} =
 Constructs the matrix over $R$ with entries as in `arr`.
 """
 function matrix(R::NCRing, arr::AbstractMatrix{T}) where {T}
+   @req !is_trivial(R) "Zero rings are currently not supported as base ring."
    if elem_type(R) === T && all(e -> parent(e) === R, arr)
       z = Generic.MatSpaceElem{elem_type(R)}(R, arr)
       return z
@@ -6643,6 +6644,7 @@ function matrix(R::NCRing, arr::AbstractMatrix{T}) where {T}
 end
 
 function matrix(R::NCRing, arr::MatElem)
+   @req !is_trivial(R) "Zero rings are currently not supported as base ring."
    return map_entries(R, arr)
 end
 
@@ -6681,6 +6683,7 @@ Constructs the $r \times c$ matrix over $R$, where the entries are taken
 row-wise from `arr`.
 """
 function matrix(R::NCRing, r::Int, c::Int, arr::AbstractVecOrMat{T}) where T
+   @req !is_trivial(R) "Zero rings are currently not supported as base ring."
    _check_dim(r, c, arr)
    ndims(arr) == 2 && return matrix(R, arr)
    if elem_type(R) === T && all(e -> parent(e) === R, arr)
@@ -7062,6 +7065,7 @@ the ring $R$.
 function matrix_space(R::NCRing, r::Int, c::Int; cached::Bool = true)
   # TODO: the 'cached' argument is ignored and mainly here for backwards compatibility
   # (and perhaps future compatibility, in case we need it again)
+  @req !is_trivial(R) "Zero rings are currently not supported as base ring."
   (r < 0 || c < 0) && error("Dimensions must be non-negative")
   T = elem_type(R)
   return MatSpace{T}(R, r, c)

src/NCPoly.jl

@@ -764,8 +764,10 @@ end
 Like [`polynomial_ring(R::NCRing, s::Symbol)`](@ref) but return only the
 polynomial ring.
 """
-polynomial_ring_only(R::T, s::Symbol; cached::Bool=true) where T<:NCRing =
-   dense_poly_ring_type(T)(R, s, cached)
+function polynomial_ring_only(R::T, s::Symbol; cached::Bool=true) where T<:NCRing
+   @req !is_trivial(R) "Zero rings are currently not supported as coefficient ring."
+   return dense_poly_ring_type(T)(R, s, cached)
+end
 
 # Simplified constructor
 

src/PuiseuxSeries.jl

@@ -24,8 +24,11 @@ object `S` will be cached so that supplying the same base ring, string and
 precision in future will return the same parent object and generator. If
 caching of the parent object is not required, `cached` can be set to `false`.
 """
-puiseux_series_ring(R::Ring, prec::Int, s::VarName; cached::Bool=true) =
-   Generic.PuiseuxSeriesRing(R, prec, Symbol(s); cached)
+function puiseux_series_ring(R::Ring, prec::Int, s::VarName; cached::Bool=true)
+   @req !is_trivial(R) "Zero rings are currently not supported as coefficient ring."
+   return Generic.PuiseuxSeriesRing(R, prec, Symbol(s); cached)
+end
 
-puiseux_series_field(R::Field, prec::Int, s::VarName; cached::Bool=true) =
-   Generic.PuiseuxSeriesField(R, prec, Symbol(s); cached)
+function puiseux_series_field(R::Field, prec::Int, s::VarName; cached::Bool=true)
+   return Generic.PuiseuxSeriesField(R, prec, Symbol(s); cached)
+end