Fix stride(A, i) for 0-dim inputs (#44090)

Fixes #44087

Author: N5N3

base/abstractarray.jl

@@ -546,7 +546,13 @@ julia> stride(A,3)
 function stride(A::AbstractArray, k::Integer)
     st = strides(A)
     k ≤ ndims(A) && return st[k]
-    return sum(st .* size(A))
+    ndims(A) == 0 && return 1
+    sz = size(A)
+    s = st[1] * sz[1]
+    for i in 2:ndims(A)
+        s += st[i] * sz[i]
+    end
+    return s
 end
 
 @inline size_to_strides(s, d, sz...) = (s, size_to_strides(s * d, sz...)...)

base/reinterpretarray.jl

@@ -149,6 +149,8 @@ StridedMatrix{T} = StridedArray{T,2}
 StridedVecOrMat{T} = Union{StridedVector{T}, StridedMatrix{T}}
 
 strides(a::Union{DenseArray,StridedReshapedArray,StridedReinterpretArray}) = size_to_strides(1, size(a)...)
+stride(A::Union{DenseArray,StridedReshapedArray,StridedReinterpretArray}, k::Integer) =
+    k ≤ ndims(A) ? strides(A)[k] : length(A)
 
 function strides(a::ReshapedReinterpretArray)
     ap = parent(a)

test/abstractarray.jl

@@ -1584,6 +1584,19 @@ end
     end
 end
 
+@testset "stride for 0 dims array #44087" begin
+    struct Fill44087 <: AbstractArray{Int,0}
+        a::Int
+    end
+    # `stride` shouldn't work if `strides` is not defined.
+    @test_throws MethodError stride(Fill44087(1), 1)
+    # It is intentionally to only check the return type. (The value is somehow arbitrary)
+    @test stride(fill(1), 1) isa Int
+    @test stride(reinterpret(Float64, fill(Int64(1))), 1) isa Int
+    @test stride(reinterpret(reshape, Float64, fill(Int64(1))), 1) isa Int
+    @test stride(Base.ReshapedArray(fill(1), (), ()), 1) isa Int
+end
+
 @testset "to_indices inference (issue #42001 #44059)" begin
     @test (@inferred to_indices([], ntuple(Returns(CartesianIndex(1)), 32))) == ntuple(Returns(1), 32)
     @test (@inferred to_indices([], ntuple(Returns(CartesianIndices(1:1)), 32))) == ntuple(Returns(Base.OneTo(1)), 32)