Separate dispatch for dropping trailing 1s (fixes for non-1 based arrays)

Author: timholy

base/abstractarray.jl

@@ -853,10 +853,15 @@ _to_subscript_indices{T}(A::AbstractArray{T,0}, i::Int) = () # TODO: REMOVE FOR
 _to_subscript_indices{T}(A::AbstractArray{T,0}, I::Int...) = () # TODO: DEPRECATE FOR #14770
 function _to_subscript_indices{T,N}(A::AbstractArray{T,N}, I::Int...) # TODO: DEPRECATE FOR #14770
     @_inline_meta
-    J, _ = IteratorsMD.split(I, Val{N})    # (maybe) drop any trailing indices
-    sz = _remaining_size(J, size(A))       # compute trailing size (overlapping the final index)
+    J, Jrem = IteratorsMD.split(I, Val{N})
+    _to_subscript_indices(A, J, Jrem)
+end
+function _to_subscript_indices(A::AbstractArray, J::Tuple, Jrem::Tuple{})
+    @_inline_meta
+    sz = _remaining_size(J, indices(A))    # compute trailing size (overlapping the final index)
     (front(J)..., _unsafe_ind2sub(sz, last(J))...) # (maybe) extend the last index
 end
+_to_subscript_indices(A, J::Tuple, Jrem::Tuple) = J # already bounds-checked, safe to drop
 _to_subscript_indices{T,N}(A::AbstractArray{T,N}, I::Vararg{Int,N}) = I
 _remaining_size(::Tuple{Any}, t::Tuple) = t
 _remaining_size(h::Tuple, t::Tuple) = (@_inline_meta; _remaining_size(tail(h), tail(t)))

test/offsetarray.jl

@@ -22,12 +22,14 @@ S = OffsetArray(view(A0, 1:2, 1:2), (-1,2))   # LinearSlow
 @test_throws ErrorException size(A, 1)
 
 # Scalar indexing
-@test A[0,3] == A[1] == S[0,3] == S[1] == 1
-@test A[1,3] == A[2] == S[1,3] == S[2] == 2
-@test A[0,4] == A[3] == S[0,4] == S[3] == 3
-@test A[1,4] == A[4] == S[1,4] == S[4] == 4
+@test A[0,3] == A[1] == A[0,3,1] == S[0,3] == S[1] == S[0,3,1] == 1
+@test A[1,3] == A[2] == A[1,3,1] == S[1,3] == S[2] == S[1,3,1] == 2
+@test A[0,4] == A[3] == A[0,4,1] == S[0,4] == S[3] == S[0,4,1] == 3
+@test A[1,4] == A[4] == A[1,4,1] == S[1,4] == S[4] == S[1,4,1] == 4
 @test_throws BoundsError A[1,1]
 @test_throws BoundsError S[1,1]
+@test_throws BoundsError A[0,3,2]
+@test_throws BoundsError S[0,3,2]
 
 # Vector indexing
 @test A[:, 3] == S[:, 3] == OffsetArray([1,2], (A.offsets[1],))