From 2fae1a102e934b13a3ff0a43f77dbd5b548e4244 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=82=B9=E3=83=8E=E3=83=AB?= <s@sunoru.com>
Date: Tue, 5 Sep 2023 02:57:32 -0400
Subject: [PATCH] Correctly set zeros with `fill!(::SubArray)` and fix its
 return value (#433)

---
 src/sparsematrix.jl                        |  5 +++--
 test/sparsematrix_constructors_indexing.jl | 17 +++++++++++++++--
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/src/sparsematrix.jl b/src/sparsematrix.jl
index 1703c870..165a7046 100644
--- a/src/sparsematrix.jl
+++ b/src/sparsematrix.jl
@@ -3179,7 +3179,8 @@ function Base.fill!(V::SubArray{Tv, <:Any, <:AbstractSparseMatrixCSC{Tv}, <:Tupl
     else
         _spsetnz_setindex!(A, convert(Tv, x), I, J)
     end
-    return _checkbuffers(A)
+    _checkbuffers(A)
+    V
 end
 """
 Helper method for immediately preceding fill! method. For all (i,j) such that i in I and
@@ -3207,7 +3208,7 @@ function _spsetz_setindex!(A::AbstractSparseMatrixCSC,
                 kI > lengthI && break
                 entrykIrow = I[kI]
             else # entrykArow == entrykIrow
-                nonzeros(A)[kA] = 0
+                nonzeros(A)[kA] = zero(eltype(A))
                 kA += 1
                 kI += 1
                 (kA > coljAlastk || kI > lengthI) && break
diff --git a/test/sparsematrix_constructors_indexing.jl b/test/sparsematrix_constructors_indexing.jl
index 5aad5628..0278c4be 100644
--- a/test/sparsematrix_constructors_indexing.jl
+++ b/test/sparsematrix_constructors_indexing.jl
@@ -342,7 +342,7 @@ end
     A = rand(5,5)
     A´ = similar(A)
     Ac = copyto!(A, B)
-    @test Ac === A 
+    @test Ac === A
     @test A == copyto!(A´, Matrix(B))
     # Test copyto!(dense, Rdest, sparse, Rsrc)
     A = rand(5,5)
@@ -1363,7 +1363,9 @@ end
     a = sprand(10, 10, 0.2)
     b = copy(a)
     sa = view(a, 1:10, 2:3)
-    fill!(sa, 0.0)
+    sa_filled = fill!(sa, 0.0)
+    # `fill!` should return the sub array instead of its parent.
+    @test sa_filled === sa
     b[1:10, 2:3] .= 0.0
     @test a == b
     A = sparse([1], [1], [Vector{Float64}(undef, 3)], 3, 3)
@@ -1375,6 +1377,17 @@ end
         B[1, jj] = [4.0, 5.0, 6.0]
     end
     @test A == B
+
+    # https://github.com/JuliaSparse/SparseArrays.jl/pull/433
+    struct Foo
+       x::Int
+    end
+    Base.zero(::Type{Foo}) = Foo(0)
+    Base.zero(::Foo) = zero(Foo)
+    C = sparse([1], [1], [Foo(3)], 3, 3)
+    sC = view(C, 1:1, 1:2)
+    fill!(sC, zero(Foo))
+    @test C[1:1, 1:2] == zeros(Foo, 1, 2)
 end
 
 using Base: swaprows!, swapcols!