Change findfirst and findlast to return cartesian indices with HasShape iterators

This represents better the shape of the iterator, and makes generators over
arrays consistent with their input array. Keep returning linear indices with
HasShape{1} iterators for consistency with vectors.

Author: nalimilan

base/array.jl

@@ -1500,7 +1500,9 @@ cat(n::Integer, x::Integer...) = reshape([x...], (ntuple(x->1, n-1)..., length(x
 
 _pairs(A::Union{AbstractArray, AbstractDict, AbstractString, Tuple, NamedTuple}) = pairs(A)
 _pairs(iter) = _pairs(IteratorSize(iter), iter)
-_pairs(::Union{HasLength, HasShape}, iter) = zip(1:length(iter), iter)
+# includes HasShape{1} for consistency with keys(::AbstractVector)
+_pairs(::Union{HasLength, HasShape{1}}, iter) = zip(1:length(iter), iter)
+_pairs(::HasShape, iter) = zip(CartesianIndices(size(iter)), iter)
 _pairs(::Union{SizeUnknown, IsInfinite}, iter) = zip(Iterators.countfrom(1), iter)
 
 """

test/arrayops.jl

@@ -498,9 +498,9 @@ end
     @test findlast(equalto(2), g2) === nothing
 
     g3 = (i % 2 for i in 1:10, j in 1:2)
-    @test findall(!iszero, g3) == 1:2:19
-    @test findfirst(!iszero, g3) == 1
-    @test findlast(!iszero, g3) == 19
+    @test findall(!iszero, g3) == findall(!iszero, collect(g3))
+    @test findfirst(!iszero, g3) == CartesianIndex(1, 1)
+    @test findlast(!iszero, g3) == CartesianIndex(9, 2)
     @test findfirst(equalto(2), g3) === nothing
     @test findlast(equalto(2), g3) === nothing
 end