Disallow ranges with Integer eltype but non-integer step

NEWS.md

@@ -131,6 +131,8 @@ New library features
 Standard library changes
 ------------------------
 * A 1-d `Zip` iterator (where `Base.IteratorSize` is `Base.HasShape{1}()`) with defined length of `n` has now also size of `(n,)` (instead of throwing an error with truncated iterators) ([#29927]).
+* It is no longer possible to create a `LinRange`, `StepRange`, or `StepRangeLen` with a
+  `<: Integer` eltype but non-integer step ([#32439]).
 * The `@timed` macro now returns a `NamedTuple` ([#34149])
 * New `supertypes(T)` function returns a tuple of all supertypes of `T` ([#34419]).
 * Sorting-related functions such as `sort` that take the keyword arguments `lt`, `rev`, `order`

base/range.jl

@@ -211,6 +211,9 @@ 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(step)
+        throw(ArgumentError("StepRange{<:Integer} cannot have non-integer step"))
+    end
     z = zero(step)
     step == z && throw(ArgumentError("step cannot be zero"))
 
@@ -344,6 +347,9 @@ 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(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 $offset"))
         new(ref, step, len, offset)
@@ -403,7 +409,11 @@ struct LinRange{T} <: AbstractRange{T}
             start == stop || throw(ArgumentError("range($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

@@ -997,6 +997,15 @@ 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)) <: Integer
+    @test_throws ArgumentError StepRange(1, 1//2, 2)
+    @test eltype(StepRangeLen{Int}(1, 1//1, 2)) <: Integer
+    @test_throws ArgumentError StepRangeLen{Int}(1, 1//2, 2)
+    @test eltype(LinRange{Int}(1, 5, 3)) <: Integer
+    @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)
@@ -1324,6 +1333,7 @@ Base.:+(x, y::NotReal) = x + y.val
 Base.zero(y::NotReal) = zero(y.val)
 Base.rem(x, y::NotReal) = rem(x, y.val)
 Base.isless(x, y::NotReal) = isless(x, y.val)
+Base.isinteger(y::NotReal) = isinteger(y.val)
 @test (:)(1, NotReal(1), 5) isa StepRange{Int,NotReal}
 
 isdefined(Main, :Furlongs) || @eval Main include("testhelpers/Furlongs.jl")