Fix linear indexing for 0D views of OffsetVectors (#39404)

* Fix linear indexing for views of OffsetVectors

* update comments

Co-authored-by: Matt Bauman <[email protected]>

Author: jishnub

base/subarray.jl

@@ -380,19 +380,19 @@ compute_offset1(parent::AbstractVector, stride1::Integer, I::Tuple{AbstractRange
 # indexing uses the indices along the given dimension.
 # If the result is one-dimensional and it's a range, then linear
 # indexing might be offset if the index itself is offset
-# Otherwise linear indexing always starts with 1.
+# Otherwise linear indexing always matches the parent.
 compute_offset1(parent, stride1::Integer, I::Tuple) =
     (@_inline_meta; compute_offset1(parent, stride1, find_extended_dims(1, I...), find_extended_inds(I...), I))
 compute_offset1(parent, stride1::Integer, dims::Tuple{Int}, inds::Tuple{Slice}, I::Tuple) =
     (@_inline_meta; compute_linindex(parent, I) - stride1*first(axes(parent, dims[1])))  # index-preserving case
 compute_offset1(parent, stride1::Integer, dims, inds::Tuple{AbstractRange}, I::Tuple) =
     (@_inline_meta; compute_linindex(parent, I) - stride1*first(axes1(inds[1]))) # potentially index-offsetting case
 compute_offset1(parent, stride1::Integer, dims, inds, I::Tuple) =
-    (@_inline_meta; compute_linindex(parent, I) - stride1)  # linear indexing starts with 1
+    (@_inline_meta; compute_linindex(parent, I) - stride1)
 function compute_linindex(parent, I::NTuple{N,Any}) where N
     @_inline_meta
     IP = fill_to_length(axes(parent), OneTo(1), Val(N))
-    compute_linindex(1, 1, IP, I)
+    compute_linindex(first(LinearIndices(parent)), 1, IP, I)
 end
 function compute_linindex(f, s, IP::Tuple, I::Tuple{ScalarIndex, Vararg{Any}})
     @_inline_meta

test/offsetarray.jl

@@ -110,6 +110,15 @@ let a1 = [11,12,13], a2 = [1 2; 3 4]
     @test_throws BoundsError i2[1:2:5]
 end
 
+# issue #37274
+let a = 1:3
+    oa = OffsetArray(a, 0:2)
+    b = @view oa[0]
+    @test b[] == b[1] == b[1,1] == 1
+    @test_throws BoundsError b[0]
+    @test_throws BoundsError b[2]
+end
+
 # logical indexing
 @test A[A .> 2] == [3,4]
 @test_throws BoundsError h[trues(2)]