Add test and fix case for multiplying size 0 arrays

Author: lkdvos

src/abstractsparsearrayinterface.jl

@@ -156,6 +156,7 @@ end
 @interface interface::AbstractSparseArrayInterface function Base.map!(
   f, a_dest::AbstractArray, as::AbstractArray...
 )
+  isempty(a_dest) && return a_dest # special case to avoid trying to access empty array
   indices = if !preserves_unstored(f, a_dest, as...)
     eachindex(a_dest)
   elseif any(a -> a_dest !== a, as)

test/test_linalg.jl

@@ -24,4 +24,22 @@ const rng = StableRNG(123)
     check2 = mul!(Array(C), Array(A), Array(B), α, β)
     @test mul!(copy(C), A, B, α, β) ≈ check2
   end
+
+  # test empty matrix
+  szA = (2, 0)
+  szB = (0, 2)
+  szC = (szA[1], szB[2])
+  for density in 0.0:0.25:1
+    C = sparserand(rng, T, szC; density)
+    A = sparserand(rng, T, szA; density)
+    B = sparserand(rng, T, szB; density)
+
+    check1 = mul!(Array(C), Array(A), Array(B))
+    @test mul!(copy(C), A, B) ≈ check1
+
+    α = rand(rng, T)
+    β = rand(rng, T)
+    check2 = mul!(Array(C), Array(A), Array(B), α, β)
+    @test mul!(copy(C), A, B, α, β) ≈ check2
+  end
 end