kron(a::Diagonal, b) ref #24980

[abraunst]

Should kron(::Diagonal, ::Union{SparseVector, SparseMatrix}) (and viceversa) return SparseMatrixCSC? (IMHO yes)
Should kron(::Diagonal, ::Matrix) (and viceversa) return SparseMatrixCSC? (this would be consistent with the recently merged #24980 in which sparse times dense gives sparse -- but currently there is an implementation for Diagonal times dense returning dense so I'm not so sure)

[andreasnoack]

Should kron(::Diagonal, ::Union{SparseVector, SparseMatrix}) (and viceversa) return SparseMatrixCSC?

Yes, I definitely think it should.

...but currently there is an implementation for Diagonal times dense returning dense so I'm not so sure)

This case is a bit complicated because of the dependency structure. To return a sparse matrix, SparseArrays would have to be a dependency of LinearAlgebra.

[abraunst]

I will close this since the first issue is resolved, and the second probably won't be,