Fix sparse Subarray fill! (JuliaLang#38021)

Co-authored-by: Matt Bauman <[email protected]>

stdlib/SparseArrays/src/sparsematrix.jl

@@ -2588,7 +2588,7 @@ function Base.fill!(V::SubArray{Tv, <:Any, <:AbstractSparseMatrixCSC{Tv}, <:Tupl
     end
 end
 """
-Helper method for immediately preceding setindex! method. For all (i,j) such that i in I and
+Helper method for immediately preceding fill! method. For all (i,j) such that i in I and
 j in J, assigns zero to A[i,j] if A[i,j] is a presently-stored entry, and otherwise does nothing.
 """
 function _spsetz_setindex!(A::AbstractSparseMatrixCSC,
@@ -2624,7 +2624,7 @@ function _spsetz_setindex!(A::AbstractSparseMatrixCSC,
     end
 end
 """
-Helper method for immediately preceding setindex! method. For all (i,j) such that i in I
+Helper method for immediately preceding fill! method. For all (i,j) such that i in I
 and j in J, assigns x to A[i,j] if A[i,j] is a presently-stored entry, and allocates and
 assigns x to A[i,j] if A[i,j] is not presently stored.
 """
@@ -2704,7 +2704,7 @@ function _spsetnz_setindex!(A::AbstractSparseMatrixCSC{Tv}, x::Tv,
                                 resize!(nzvalA, nnzA)
                             end
                             r = rowidx:(rowidx+(new_stop-new_ptr))
-                            rowvalA[r] .= I[new_ptr:new_stop]
+                            rowvalA[r] .= I isa Number ? I : I[new_ptr:new_stop]
                             for rr in r
                                 nzvalA[rr] = x
                             end

stdlib/SparseArrays/test/sparse.jl

@@ -1057,6 +1057,12 @@ end
     @test a[1,:] == sparse([1; 1; 3:10])
     a[1:0,2] .= 1
     @test a[:,2] == sparse([1:10;])
+    a[3,2:3] .= 1 # one stored, one new value
+    @test a[3,2:3] == sparse([1; 1])
+    a[5:6,1] .= 1 # only new values
+    @test a[:,1] == sparse([1; 0; 0; 0; 1; 1; 0; 0; 0; 0;])
+    a[2:4,2:3] .= 3 # two ranges
+    @test nnz(a) == 24
 
     @test_throws BoundsError a[:,11] = spzeros(10,1)
     @test_throws BoundsError a[11,:] = spzeros(1,10)