LinearAlgebra: Don't assume AbstractVector supports deleteat! (#46672)

stdlib/LinearAlgebra/src/LinearAlgebra.jl

@@ -469,6 +469,10 @@ _evview(S::SymTridiagonal) = @view S.ev[begin:begin + length(S.dv) - 2]
 _zeros(::Type{T}, b::AbstractVector, n::Integer) where {T} = zeros(T, max(length(b), n))
 _zeros(::Type{T}, B::AbstractMatrix, n::Integer) where {T} = zeros(T, max(size(B, 1), n), size(B, 2))
 
+# convert to Vector, if necessary
+_makevector(x::Vector) = x
+_makevector(x::AbstractVector) = Vector(x)
+
 # append a zero element / drop the last element
 _pushzero(A) = (B = similar(A, length(A)+1); @inbounds B[begin:end-1] .= A; @inbounds B[end] = zero(eltype(B)); B)
 _droplast!(A) = deleteat!(A, lastindex(A))

stdlib/LinearAlgebra/src/bidiag.jl

@@ -206,8 +206,9 @@ similar(B::Bidiagonal, ::Type{T}) where {T} = Bidiagonal(similar(B.dv, T), simil
 similar(B::Bidiagonal, ::Type{T}, dims::Union{Dims{1},Dims{2}}) where {T} = zeros(T, dims...)
 
 function kron(A::Diagonal, B::Bidiagonal)
- kdv = kron(diag(A), B.dv)
- kev = _droplast!(kron(diag(A), _pushzero(B.ev)))
+ # `_droplast!` is only guaranteed to work with `Vector`
+ kdv = _makevector(kron(diag(A), B.dv))
+ kev = _droplast!(_makevector(kron(diag(A), _pushzero(B.ev))))
  Bidiagonal(kdv, kev, B.uplo)
 end
 

stdlib/LinearAlgebra/src/diagonal.jl

@@ -605,9 +605,10 @@ function kron(A::Diagonal, B::SymTridiagonal)
  SymTridiagonal(kdv, kev)
 end
 function kron(A::Diagonal, B::Tridiagonal)
- kd = kron(diag(A), B.d)
- kdl = _droplast!(kron(diag(A), _pushzero(B.dl)))
- kdu = _droplast!(kron(diag(A), _pushzero(B.du)))
+ # `_droplast!` is only guaranteed to work with `Vector`
+ kd = _makevector(kron(diag(A), B.d))
+ kdl = _droplast!(_makevector(kron(diag(A), _pushzero(B.dl))))
+ kdu = _droplast!(_makevector(kron(diag(A), _pushzero(B.du))))
  Tridiagonal(kdl, kd, kdu)
 end
 

stdlib/LinearAlgebra/test/diagonal.jl

@@ -462,13 +462,36 @@ end
  @test kron(Ad, Ad).diag == kron([1, 2, 3], [1, 2, 3])
 end
 
-@testset "kron (issue #46456)" begin
- A = Diagonal(randn(10))
- BL = Bidiagonal(randn(10), randn(9), :L)
- BU = Bidiagonal(randn(10), randn(9), :U)
- C = SymTridiagonal(randn(10), randn(9))
- Cl = SymTridiagonal(randn(10), randn(10))
- D = Tridiagonal(randn(9), randn(10), randn(9))
+# Define a vector type that does not support `deleteat!`, to ensure that `kron` handles this
+struct SimpleVector{T} <: AbstractVector{T}
+ vec::Vector{T}
+end
+SimpleVector(x::SimpleVector) = SimpleVector(Vector(x.vec))
+SimpleVector{T}(::UndefInitializer, n::Integer) where {T} = SimpleVector(Vector{T}(undef, n))
+Base.:(==)(x::SimpleVector, y::SimpleVector) = x == y
+Base.axes(x::SimpleVector) = axes(x.vec)
+Base.convert(::Type{Vector{T}}, x::SimpleVector) where {T} = convert(Vector{T}, x.vec)
+Base.convert(::Type{Vector}, x::SimpleVector{T}) where {T} = convert(Vector{T}, x)
+Base.convert(::Type{Array{T}}, x::SimpleVector) where {T} = convert(Vector{T}, x)
+Base.convert(::Type{Array}, x::SimpleVector) = convert(Vector, x)
+Base.copyto!(x::SimpleVector, y::SimpleVector) = (copyto!(x.vec, y.vec); x)
+Base.eltype(::Type{SimpleVector{T}}) where {T} = T
+Base.getindex(x::SimpleVector, ind...) = getindex(x.vec, ind...)
+Base.kron(x::SimpleVector, y::SimpleVector) = SimpleVector(kron(x.vec, y.vec))
+Base.promote_rule(::Type{<:AbstractVector{T}}, ::Type{SimpleVector{U}}) where {T,U} = Vector{promote_type(T, U)}
+Base.promote_rule(::Type{SimpleVector{T}}, ::Type{SimpleVector{U}}) where {T,U} = SimpleVector{promote_type(T, U)}
+Base.setindex!(x::SimpleVector, val, ind...) = (setindex!(x.vec, val, ind...), x)
+Base.similar(x::SimpleVector, ::Type{T}) where {T} = SimpleVector(similar(x.vec, T))
+Base.similar(x::SimpleVector, ::Type{T}, dims::Dims{1}) where {T} = SimpleVector(similar(x.vec, T, dims))
+Base.size(x::SimpleVector) = size(x.vec)
+
+@testset "kron (issue #46456)" for repr in Any[identity, SimpleVector]
+ A = Diagonal(repr(randn(10)))
+ BL = Bidiagonal(repr(randn(10)), repr(randn(9)), :L)
+ BU = Bidiagonal(repr(randn(10)), repr(randn(9)), :U)
+ C = SymTridiagonal(repr(randn(10)), repr(randn(9)))
+ Cl = SymTridiagonal(repr(randn(10)), repr(randn(10)))
+ D = Tridiagonal(repr(randn(9)), repr(randn(10)), repr(randn(9)))
  @test kron(A, BL)::Bidiagonal == kron(Array(A), Array(BL))
  @test kron(A, BU)::Bidiagonal == kron(Array(A), Array(BU))
  @test kron(A, C)::SymTridiagonal == kron(Array(A), Array(C))