Base.show fails with structural matrices with non-number elements

[longemen3000]

Some matrices (SparseMatrixCSC and Diagonal, as far as i know) depend on a type defining iszero(x::T) and zero(Type{T}) to work. a MWE:

show(IOBuffer(),MIME"text/plain"(),Diagonal(fill(nothing,3)))

version info.

julia> versioninfo()
Julia Version 1.9.1
Commit 147bdf428c (2023-06-07 08:27 UTC)
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: 8 × Intel(R) Core(TM) i7-4720HQ CPU @ 2.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-14.0.6 (ORCJIT, haswell)
  Threads: 4 on 8 virtual cores
Environment:
  JULIA_NUM_THREADS = 4

related:

korsbo/Latexify.jl#269

[longemen3000]

this could be solved by:

1. defining Base.isstored(A::Diagonal,i::Int,j::Int) == i == j ? isstored(A.diag,i) : false

2. Replacing the code in arrayshow.jl:

   julia/base/arrayshow.jl

   Lines 67 to 72 in 36e188f

   	for i in rows # plumb down and see what largest element sizes are
   	if isassigned(X,i,j)
   	aij = alignment(io, X[i,j])::Tuple{Int,Int}
   	else
   	aij = undef_ref_alignment
   	end

to:

if isstored(X,i,j) && isassigned(X,i,j)
    aij = alignment(io, X[i,j])::Tuple{Int,Int}
else
    aij = undef_ref_alignment
end

[vtjnash]

I am not certain about the proposed fix there, since the code expects getindex to work, and then calls Base.replace_in_print_matrix to call Base.replace_with_centered_mark on the resulting element repr.

[longemen3000]

The issue is not fixed with #50391, but defines the necessary functions to work on a fix

[vtjnash]

Right, github got confused by the text there, but my uncertainty remains over the proposed answer here

[longemen3000]

Yeah, I will need to see what to do about that, but at least there is now a way to detect if an element of a matrix is stored or not

[vtjnash]

Yeah, that seemed to be the goal of a5e032e (#33821), which originally started to add that.