Explicitly compute stride in unaliascopy for SubArray (#54102)

Fix #54100 by computing the
stride and offset explicitly. This is unlikely to be a performance
concern, so we don't need to hard-code this.

(cherry picked from commit 159f4d7)

base/subarray.jl

@@ -115,11 +115,14 @@ function unaliascopy(V::SubArray{T,N,A,I,LD}) where {T,N,A<:Array,I<:Tuple{Varar
     trimmedpind = _trimmedpind(V.indices...)
     vdest = trimmedpind isa Tuple{Vararg{Union{Slice,Colon}}} ? dest : view(dest, trimmedpind...)
     copyto!(vdest, view(V, _trimmedvind(V.indices...)...))
-    SubArray{T,N,A,I,LD}(dest, map(_trimmedindex, V.indices), 0, Int(LD))
+    indices = map(_trimmedindex, V.indices)
+    stride1 = LD ? compute_stride1(dest, indices) : 0
+    offset1 = LD ? compute_offset1(dest, stride1, indices) : 0
+    SubArray{T,N,A,I,LD}(dest, indices, offset1, stride1)
 end
 # Get the proper trimmed shape
 _trimmedshape(::ScalarIndex, rest...) = (1, _trimmedshape(rest...)...)
-_trimmedshape(i::AbstractRange, rest...) = (maximum(i), _trimmedshape(rest...)...)
+_trimmedshape(i::AbstractRange, rest...) = (isempty(i) ? zero(eltype(i)) : maximum(i), _trimmedshape(rest...)...)
 _trimmedshape(i::Union{UnitRange,StepRange,OneTo}, rest...) = (length(i), _trimmedshape(rest...)...)
 _trimmedshape(i::AbstractArray{<:ScalarIndex}, rest...) = (length(i), _trimmedshape(rest...)...)
 _trimmedshape(i::AbstractArray{<:AbstractCartesianIndex{0}}, rest...) = _trimmedshape(rest...)

test/subarray.jl

@@ -826,6 +826,25 @@ end
     @test @inferred(Base.unaliascopy(V))::typeof(V) == V == A[i1, 1:5, i2, i3]
     V = view(A, i1, 1:5, i3, i2)
     @test @inferred(Base.unaliascopy(V))::typeof(V) == V == A[i1, 1:5, i3, i2]
+
+    @testset "custom ranges" begin
+        struct MyStepRange{T} <: OrdinalRange{T,T}
+            r::StepRange{T,T}
+        end
+
+        for f in (:first, :last, :step, :length, :size)
+            @eval Base.$f(r::MyStepRange) = $f(r.r)
+        end
+        Base.getindex(r::MyStepRange, i::Int) = r.r[i]
+
+        a = rand(6)
+        V = view(a, MyStepRange(2:2:4))
+        @test @inferred(Base.unaliascopy(V))::typeof(V) == V
+
+        # empty range
+        V = view(a, MyStepRange(2:2:1))
+        @test @inferred(Base.unaliascopy(V))::typeof(V) == V
+    end
 end
 
 @testset "issue #27632" begin