Specialize union for OneTo (#35577)

Author: goretkin

base/range.jl

@@ -762,6 +762,7 @@ function ==(r::AbstractRange, s::AbstractRange)
 end
 
 intersect(r::OneTo, s::OneTo) = OneTo(min(r.stop,s.stop))
+union(r::OneTo, s::OneTo) = OneTo(max(r.stop,s.stop))
 
 intersect(r::AbstractUnitRange{<:Integer}, s::AbstractUnitRange{<:Integer}) = max(first(r),first(s)):min(last(r),last(s))
 

test/ranges.jl

@@ -1232,6 +1232,7 @@ end
             @test i == (k += 1)
         end
         @test intersect(r, Base.OneTo(2)) == Base.OneTo(2)
+        @test union(r, Base.OneTo(4)) == Base.OneTo(4)
         @test intersect(r, 0:5) == 1:3
         @test intersect(r, 2) === intersect(2, r) === 2:2
         @test findall(in(r), r) === findall(in(1:length(r)), r) ===