Correctly set zeros with fill!(::SubArray) and fix its return value

[sunoru]

This PR includes two fixes:

1

It is a simple obvious fix to the problem when one tries to do something like the following

using SparseArrays, StaticArrays
const Vec2 = SVector{2, Float64}
A = rand(Vec2, 2, 2) |> sparse
fill!(view(A, :, :), zero(Vec2))

Without the fix, it throws

ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type SVector{2, Float64}

Closest candidates are:
  convert(::Type{T}, ::Factorization) where T<:AbstractArray
   @ LinearAlgebra /usr/share/julia/stdlib/v1.9/LinearAlgebra/src/factorization.jl:59
  convert(::Type{SVector{N, T}}, ::CartesianIndex{N}) where {N, T}
   @ StaticArrays ~/.julia/packages/StaticArrays/jA1zK/src/SVector.jl:13
  convert(::Type{SA}, ::Tuple) where SA<:StaticArray
   @ StaticArrays ~/.julia/packages/StaticArrays/jA1zK/src/convert.jl:179
  ...

Stacktrace:
 [1] setindex!(A::Vector{SVector{2, Float64}}, x::Int64, i1::Int64)
   @ Base ./array.jl:969
 [2] _spsetz_setindex!
   @ /usr/share/julia/stdlib/v1.9/SparseArrays/src/sparsematrix.jl:3033 [inlined]
 [3] fill!(V::SubArray{SVector{2, Float64}, 1, SparseMatrixCSC{SVector{2, Float64}, Int64}, Tuple{Base.Slice{Base.OneTo{Int64}}, Int64}, false}, x::SVector{2, Float64})
   @ SparseArrays /usr/share/julia/stdlib/v1.9/SparseArrays/src/sparsematrix.jl:3001
 [4] top-level scope
   @ REPL[61]:1

2

fill!(A, ...) should always return A, but without the fix, it returns A.parent for sub arrays of the sparse arrays, if zeros are being set.

[codecov]

Codecov Report

Merging #433 (5b32f28) into main (4e6776a) will increase coverage by 0.78%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #433      +/-   ##
==========================================
+ Coverage   92.42%   93.20%   +0.78%     
==========================================
  Files          12       12              
  Lines        7667     7668       +1     
==========================================
+ Hits         7086     7147      +61     
+ Misses        581      521      -60     

Files Changed	Coverage Δ
src/sparsematrix.jl	95.68% <100.00%> (+<0.01%)	⬆️

... and 2 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[dkarrasch]

Do you think you could add a test for this case? Maybe there is some number type that is not convertible to from an integer 0? Perhaps some unitful number type should work?

[sunoru]

OK I will try to add the tests.

Actually I just found another issue related to the fill! function for sub arrays that it should always returns the given array (the first argument) instead of the parent of that array. Should I submit another PR or can I also fix it here since I think they are both small fixes?

[sunoru]

There is no number type except Irrational that is not convertible to from an integer 0, but it also doesn't have a zero value.

The only common use case I can imagine is for SVectors, but for the test purpose I can just declare a custom struct.

[dkarrasch]

Actually I just found another issue related to the fill! function for sub arrays

Fix here, but for easier review, please submit first a commit with a test that currently fails, and then another commit with the fix.