Fixing abs for Rational{<:Unsigned} (#29561)

* Fix abs for Rational{<:Unsigned}

* Add tests for abs(x::Rational)

(cherry picked from commit 4eb1a93)

base/rational.jl

@@ -226,6 +226,8 @@ signbit(x::Rational) = signbit(x.num)
 copysign(x::Rational, y::Real) = copysign(x.num,y) // x.den
 copysign(x::Rational, y::Rational) = copysign(x.num,y.num) // x.den
 
+abs(x::Rational) = Rational(abs(x.num), x.den)
+
 typemin(::Type{Rational{T}}) where {T<:Integer} = -one(T)//zero(T)
 typemax(::Type{Rational{T}}) where {T<:Integer} = one(T)//zero(T)
 

test/rational.jl

@@ -96,6 +96,11 @@ using Test
  @test !(1//3 < NaN)
  @test !(1//3 == NaN)
  @test !(1//3 > NaN)
+
+ # PR 29561
+ @test abs(one(Rational{UInt})) === one(Rational{UInt})
+ @test abs(one(Rational{Int})) === one(Rational{Int})
+ @test abs(-one(Rational{Int})) === one(Rational{Int})
 end
 
 @testset "Rational methods" begin