Fix assignment to 0-dim array indexed by CartesianIndices{0} (#34893)

* Fix assignment to 0-dim array indexed by CartesianIndices{0}

* Fix assigning element into ≥1-dim arrays from 0-dim array

base/multidimensional.jl

@@ -384,6 +384,9 @@ module IteratorsMD
     # When used as indices themselves, CartesianIndices can simply become its tuple of ranges
     @inline to_indices(A, inds, I::Tuple{CartesianIndices, Vararg{Any}}) =
         to_indices(A, inds, (I[1].indices..., tail(I)...))
+    # but preserve CartesianIndices{0} as they consume a dimension.
+    @inline to_indices(A, inds, I::Tuple{CartesianIndices{0},Vararg{Any}}) =
+        (first(I), to_indices(A, inds, tail(I))...)
 
     @inline function in(i::CartesianIndex{N}, r::CartesianIndices{N}) where {N}
         _in(true, i.I, first(r).I, last(r).I)

test/arrayops.jl

@@ -2684,6 +2684,30 @@ end
     end
     @test !checkbounds(Bool, rand(3,3,3), :, CartesianIndex(0,0):CartesianIndex(1,1))
     @test !checkbounds(Bool, rand(3,3,3), CartesianIndex(0,0):CartesianIndex(1,1), :)
+
+    CI0 = CartesianIndices(())
+    # 0-dimensional
+    @test setindex!(fill(0.0), fill(1.0), CI0) == fill(1.0)
+    @test setindex!(fill(0.0), fill(1.0), CI0, CI0) == fill(1.0)
+    @test setindex!(fill(0.0), fill(1.0), :, CI0) == fill(1.0)
+    @test setindex!(fill(0.0), fill(1.0), CI0, :) == fill(1.0)
+    @test setindex!(fill(0.0), fill(1.0), :, CI0, CI0) == fill(1.0)
+    @test setindex!(fill(0.0), fill(1.0), CI0, :, CI0) == fill(1.0)
+    @test setindex!(fill(0.0), fill(1.0), CI0, CI0, :) == fill(1.0)
+    @test setindex!(fill(fill(0.0)), fill(fill(1.0)), CI0) == fill(fill(1.0))
+    # 1-dimensional
+    @test setindex!(zeros(2), ones(2), :, CI0) == ones(2)
+    @test setindex!(zeros(2), ones(2), CI0, :) == ones(2)
+    @test setindex!(zeros(2), ones(2), :, CI0, CI0) == ones(2)
+    @test setindex!(zeros(2), ones(2), CI0, :, CI0) == ones(2)
+    @test setindex!(zeros(2), ones(2), CI0, CI0, :) == ones(2)
+    @test setindex!([fill(0.0)], fill(1.0), 1) == [fill(1.0)]
+    # 0-dimensional assigment into ≥1-dimensional arrays
+    @test setindex!(zeros(2), fill(1.0), 1, CI0) == [1.0, 0.0]
+    @test setindex!(zeros(2), fill(1.0), CI0, 1) == [1.0, 0.0]
+    @test setindex!(zeros(2,2), fill(1.0), 1, 1, CI0) == [1.0 0.0; 0.0 0.0]
+    @test setindex!(zeros(2,2), fill(1.0), 1, CI0, 1) == [1.0 0.0; 0.0 0.0]
+    @test setindex!(zeros(2,2), fill(1.0), CI0, 1, 1) == [1.0 0.0; 0.0 0.0]
 end
 
 # Throws ArgumentError for negative dimensions in Array