Ensure that collect(::AbstractArray) always returns an Array (#21257)

The docstring specifies that the return type is `Array`, but `similar` isn't guaranteed to return an `Array`. (Exceptions include AxisArrays, OffsetArrays, etc.)

Author: timholy

base/array.jl

@@ -383,6 +383,8 @@ julia> collect(1:2:13)
 """
 collect(itr) = _collect(1:1 #= Array =#, itr, iteratoreltype(itr), iteratorsize(itr))
 
+collect(A::AbstractArray) = _collect_indices(indices(A), A)
+
 collect_similar(cont, itr) = _collect(cont, itr, iteratoreltype(itr), iteratorsize(itr))
 
 _collect(cont, itr, ::HasEltype, isz::Union{HasLength,HasShape}) =
@@ -396,6 +398,14 @@ function _collect(cont, itr, ::HasEltype, isz::SizeUnknown)
     return a
 end
 
+_collect_indices(::Tuple{}, A) = copy!(Array{eltype(A)}(), A)
+_collect_indices(indsA::Tuple{Vararg{OneTo}}, A) =
+    copy!(Array{eltype(A)}(length.(indsA)), A)
+function _collect_indices(indsA, A)
+    B = Array{eltype(A)}(length.(indsA))
+    copy!(B, CartesianRange(indices(B)), A, CartesianRange(indsA))
+end
+
 if isdefined(Core, :Inference)
     _default_eltype(itrt::ANY) = Core.Inference.return_type(first, Tuple{itrt})
 else

test/offsetarray.jl

@@ -281,6 +281,7 @@ v = OffsetArray(v0, (-3,))
 @test endof(v) == 1
 @test v ≈ v
 @test indices(v') === (Base.OneTo(1),-2:1)
+@test parent(v) == collect(v)
 rv = reverse(v)
 @test indices(rv) == indices(v)
 @test rv[1] == v[-2]
@@ -294,6 +295,7 @@ A = OffsetArray(rand(4,4), (-3,5))
 @test A ≈ A
 @test indices(A') === (6:9, -2:1)
 @test parent(A') == parent(A)'
+@test collect(A) == parent(A)
 @test maximum(A) == maximum(parent(A))
 @test minimum(A) == minimum(parent(A))
 @test extrema(A) == extrema(parent(A))