handle the condition in in when step(r::AbstractRange) equals 0 (#41974)

* handle the condition in `in` when `step` equals 0

Using `in` when `step(r::AbstractRange) == 0` results in an error.

Handle this case by using boolean logic for both the definitions to
which this case applies (`x::Real` and `x::AbstractChar`).
First, check if the step equals zero and if `x` (the value) equals the
reference value before performing the invalid `mod` operation.

Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>

* add tests for `StepRangeLen` when step equals 0

Add two tests (one which passes and another which fails) each,
for `in` with `StepRangeLen` that has step = 0, where `x` is of
type `Real` and `AbstractChar`.

Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>

Author: thazhemadam

base/range.jl

@@ -1382,11 +1382,13 @@ in(x::T, r::AbstractRange{T}) where {T} = _in_range(x, r)
 in(x::Integer, r::AbstractUnitRange{<:Integer}) = (first(r) <= x) & (x <= last(r))
 
 in(x::Real, r::AbstractRange{T}) where {T<:Integer} =
-    isinteger(x) && !isempty(r) && x >= minimum(r) && x <= maximum(r) &&
-        (mod(convert(T,x),step(r))-mod(first(r),step(r)) == 0)
+    isinteger(x) && !isempty(r) &&
+    (iszero(step(r)) ? x == first(r) : (x >= minimum(r) && x <= maximum(r) &&
+        (mod(convert(T,x),step(r))-mod(first(r),step(r)) == 0)))
 in(x::AbstractChar, r::AbstractRange{<:AbstractChar}) =
-    !isempty(r) && x >= minimum(r) && x <= maximum(r) &&
-        (mod(Int(x) - Int(first(r)), step(r)) == 0)
+    !isempty(r) &&
+    (iszero(step(r)) ? x == first(r) : (x >= minimum(r) && x <= maximum(r) &&
+        (mod(Int(x) - Int(first(r)), step(r)) == 0)))
 
 # Addition/subtraction of ranges
 

test/ranges.jl

@@ -2164,3 +2164,20 @@ end
 @test length(range(1, 100, length=big(100)^100)) == big(100)^100
 @test length(range(big(1), big(100)^100, length=big(100)^100)) == big(100)^100
 @test length(0 * (1:big(100)^100)) == big(100)^100
+
+@testset "issue #41784" begin
+    # tests `in` when step equals 0
+    # test for Int
+    x = 41784
+    @test (x in StepRangeLen(x, 0, 0)) == false
+    @test (x in StepRangeLen(x, 0, rand(1:100))) == true
+    @test ((x - 1) in StepRangeLen(x, 0, rand(1:100))) == false
+    @test ((x + 1) in StepRangeLen(x, 0, rand(1:100))) == false
+
+    # test for Char
+    x = 'z'
+    @test (x in StepRangeLen(x, 0, 0)) == false
+    @test (x in StepRangeLen(x, 0, rand(1:100))) == true
+    @test ((x - 1) in StepRangeLen(x, 0, rand(1:100))) == false
+    @test ((x + 1) in StepRangeLen(x, 0, rand(1:100))) == false
+end