Disallow ranges with Integer eltype but non-integer step (JuliaLang#3…

…2439)

NEWS.md

@@ -113,6 +113,7 @@ New library features
 Standard library changes
 ------------------------
 
+* It is no longer possible to create a `LinRange`, `StepRange`, or `StepRangeLen` with a `<: Integer` eltype but non-integer step ([#32439]).
 * `pkg> precompile` is now parallelized through depth-first precompilation of dependencies. Errors will only throw for
  direct dependencies listed in the `Project.toml`.
 * `pkg> precompile` is now automatically triggered whenever Pkg changes the active manifest. Auto-precompilation will

base/range.jl

@@ -214,6 +214,9 @@ function steprange_last(start::T, step, stop) where T
  if isa(start,AbstractFloat) || isa(step,AbstractFloat)
  throw(ArgumentError("StepRange should not be used with floating point"))
  end
+ if isa(start,Integer) && !isinteger(start + step)
+ throw(ArgumentError("StepRange{<:Integer} cannot have non-integer step"))
+ end
  z = zero(step)
  step == z && throw(ArgumentError("step cannot be zero"))
 
@@ -351,6 +354,9 @@ struct StepRangeLen{T,R,S} <: AbstractRange{T}
  offset::Int # the index of ref
 
  function StepRangeLen{T,R,S}(ref::R, step::S, len::Integer, offset::Integer = 1) where {T,R,S}
+ if T <: Integer && !isinteger(ref + step)
+ throw(ArgumentError("StepRangeLen{<:Integer} cannot have non-integer step"))
+ end
  len >= 0 || throw(ArgumentError("length cannot be negative, got $len"))
  1 <= offset <= max(1,len) || throw(ArgumentError("StepRangeLen: offset must be in [1,$len], got $offset"))
  new(ref, step, len, offset)
@@ -410,7 +416,11 @@ struct LinRange{T} <: AbstractRange{T}
  start == stop || throw(ArgumentError("range($start, stop=$stop, length=$len): endpoints differ"))
  return new(start, stop, 1, 1)
  end
- new(start,stop,len,max(len-1,1))
+ lendiv = max(len-1, 1)
+ if T <: Integer && !iszero(mod(stop-start, lendiv))
+ throw(ArgumentError("LinRange{<:Integer} cannot have non-integer step"))
+ end
+ new(start,stop,len,lendiv)
  end
 end
 

test/ranges.jl

@@ -1002,6 +1002,15 @@ end
  @test eltype(['a':'z', 1:2]) == (StepRange{T,Int} where T)
 end
 
+@testset "Ranges with <:Integer eltype but non-integer step (issue #32419)" begin
+ @test eltype(StepRange(1, 1//1, 2)) === Int
+ @test_throws ArgumentError StepRange(1, 1//2, 2)
+ @test eltype(StepRangeLen{Int}(1, 1//1, 2)) === Int
+ @test_throws ArgumentError StepRangeLen{Int}(1, 1//2, 2)
+ @test eltype(LinRange{Int}(1, 5, 3)) === Int
+ @test_throws ArgumentError LinRange{Int}(1, 5, 4)
+end
+
 @testset "LinRange ops" begin
  @test 2*LinRange(0,3,4) == LinRange(0,6,4)
  @test LinRange(0,3,4)*2 == LinRange(0,6,4)