From c3fc5ad1747141229339dc3e898665a96d390e51 Mon Sep 17 00:00:00 2001
From: jishnub <jishnub@users.noreply.github.com>
Date: Sat, 29 May 2021 14:40:20 +0400
Subject: [PATCH] indexing OneTo with IdentityUnitRange preserves axes

---
 base/indices.jl |  4 ++++
 test/ranges.jl  | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/base/indices.jl b/base/indices.jl
index 462e62c6d8883..ef9e2c52ca6a3 100644
--- a/base/indices.jl
+++ b/base/indices.jl
@@ -400,6 +400,10 @@ getindex(S::IdentityUnitRange, i::StepRange{<:Integer}) = (@_inline_meta; @bound
 show(io::IO, r::IdentityUnitRange) = print(io, "Base.IdentityUnitRange(", r.indices, ")")
 iterate(S::IdentityUnitRange, s...) = iterate(S.indices, s...)
 
+# For OneTo, the values and indices of the values are identical, so this may be defined in Base.
+# In general such an indexing operation would produce offset ranges
+getindex(S::OneTo, I::IdentityUnitRange{<:AbstractUnitRange{<:Integer}}) = (@_inline_meta; @boundscheck checkbounds(S, I); I)
+
 """
     LinearIndices(A::AbstractArray)
 
diff --git a/test/ranges.jl b/test/ranges.jl
index eb4fadfac6253..b06bae88b02a7 100644
--- a/test/ranges.jl
+++ b/test/ranges.jl
@@ -1933,3 +1933,13 @@ end
     @test (10:-1:1) * 0.1 == 1:-0.1:0.1
     @test 0.2 * (-2:2:2) == [-0.4, 0, 0.4]
 end
+
+@testset "Indexing OneTo with IdentityUnitRange" begin
+    for endpt in Any[10, big(10), UInt(10)]
+        r = Base.OneTo(endpt)
+        inds = Base.IdentityUnitRange(3:5)
+        rs = r[inds]
+        @test rs === inds
+        @test_throws BoundsError r[Base.IdentityUnitRange(-1:100)]
+    end
+end