Fix setting block to zero with broadcasting notation

NDTensors/src/lib/BlockSparseArrays/src/abstractblocksparsearray/wrappedabstractblocksparsearray.jl

@@ -185,7 +185,22 @@ function Base.setindex!(a::BlockSparseArrayLike{<:Any,1}, value, I::Block{1})
   return a
 end
 
+function Base.fill!(a::AbstractBlockSparseArray, value)
+  if iszero(value)
+    # This drops all of the blocks.
+    sparse_zero!(blocks(a))
+    return a
+  end
+  blocksparse_fill!(a, value)
+  return a
+end
+
 function Base.fill!(a::BlockSparseArrayLike, value)
+  # TODO: Even if `iszero(value)`, this doesn't drop
+  # blocks from `a`, and additionally allocates
+  # new blocks filled with zeros, unlike
+  # `fill!(a::AbstractBlockSparseArray, value)`.
+  # Consider changing that behavior when possible.
   blocksparse_fill!(a, value)
   return a
 end

NDTensors/src/lib/BlockSparseArrays/src/blocksparsearrayinterface/blocksparsearrayinterface.jl

@@ -96,11 +96,6 @@ function blocksparse_setindex!(
 end
 
 function blocksparse_fill!(a::AbstractArray, value)
-  if iszero(value)
-    # This drops all of the blocks.
-    sparse_zero!(blocks(a))
-    return a
-  end
   for b in BlockRange(a)
     # We can't use:
     # ```julia

NDTensors/src/lib/BlockSparseArrays/test/test_basics.jl

@@ -92,6 +92,16 @@ include("TestBlockSparseArraysUtils.jl")
     @test block_nstored(a) == 1
     @test nstored(a) == 2 * 4
 
+    a = BlockSparseArray{elt}([2, 3], [3, 4])
+    a[Block(1, 2)] .= 0
+    @test eltype(a) == elt
+    @test iszero(a[Block(1, 1)])
+    @test iszero(a[Block(2, 1)])
+    @test iszero(a[Block(1, 2)])
+    @test iszero(a[Block(2, 2)])
+    @test block_nstored(a) == 1
+    @test nstored(a) == 2 * 4
+
     a = BlockSparseArray{elt}(undef, ([2, 3], [3, 4]))
     @views for b in [Block(1, 2), Block(2, 1)]
       a[b] = randn(elt, size(a[b]))