fix #37199, indexing for 1-d views with offset ranges (#37204)

We had been assuming that IdentityUnitRange matched the indices of the parent (like Slices) but they define their own offset axes. Further, other `AbstractRanges` may be similarly offset. We do not need to consider other offset `AbstractArrays` as this code only applies to `IndexLinear` `SubArray`s.

Author: mbauman

base/subarray.jl

@@ -366,17 +366,20 @@ end
 # The running sum is `f`; the cumulative stride product is `s`.
 # If the parent is a vector, then we offset the parent's own indices with parameters of I
 compute_offset1(parent::AbstractVector, stride1::Integer, I::Tuple{AbstractRange}) =
-    (@_inline_meta; first(I[1]) - first(axes1(I[1]))*stride1)
+    (@_inline_meta; first(I[1]) - stride1*first(axes1(I[1])))
 # If the result is one-dimensional and it's a Colon, then linear
-# indexing uses the indices along the given dimension. Otherwise
-# linear indexing always starts with 1.
+# 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.
 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{Union{Slice, IdentityUnitRange}}, I::Tuple) =
+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
-
 function compute_linindex(parent, I::NTuple{N,Any}) where N
     @_inline_meta
     IP = fill_to_length(axes(parent), OneTo(1), Val(N))

test/subarray.jl

@@ -656,6 +656,33 @@ end
     @test _test_27632(view(ones(Int64, (1, 1, 1)), 1, 1, 1)) === nothing
 end
 
+@testset "issue #37199: 1-d views with offset range indices" begin
+    b = zeros(6, 3)
+    b[Base.IdentityUnitRange(4:6), 2] .= 3
+    @test b == [zeros(6, 1) [0,0,0,3,3,3] zeros(6,1)]
+    b[4, Base.IdentityUnitRange(2:3)] .= 4
+    @test b == [zeros(6,1) [0,0,0,4,3,3] [0,0,0,4,0,0]]
+    b[Base.IdentityUnitRange(2:3), :] .= 5
+    @test b == [zeros(1, 3); fill(5, 2, 3); [zeros(3) [4,3,3] [4,0,0]]]
+    b[:, Base.IdentityUnitRange(3:3)] .= 6
+    @test b == [[zeros(1, 2); fill(5, 2, 2); [zeros(3) [4,3,3]]] fill(6, 6)]
+
+    A = reshape(1:5*7*11, 11, 7, 5)
+    inds = (1:4, 2:5, 2, :, fill(3))
+    offset(x) = x
+    offset(r::UnitRange) = Base.IdentityUnitRange(r)
+    for i1 in inds
+        for i2 in inds
+            for i3 in inds
+                vo = @view A[offset(i1), offset(i2), offset(i3)]
+                v = @view A[i1, i2, i3]
+                @test first(vo) == first(v) == first(A[i1, i2, i3])
+                @test collect(A[i1, i2, i3]) == collect(vo) == collect(v)
+            end
+        end
+    end
+end
+
 @testset "issue #29608; contiguousness" begin
     @test Base.iscontiguous(view(ones(1), 1))
     @test Base.iscontiguous(view(ones(10), 1:10))