RNG: fix Sampler selection for GLOBAL_RNG (#33172)

Author: rfourquet

stdlib/Random/src/RNGs.jl

@@ -313,6 +313,9 @@ struct _GLOBAL_RNG <: AbstractRNG
     global const GLOBAL_RNG = _GLOBAL_RNG.instance
 end
 
+# GLOBAL_RNG currently represents a MersenneTwister
+typeof_rng(::_GLOBAL_RNG) = MersenneTwister
+
 copy!(dst::MersenneTwister, ::_GLOBAL_RNG) = copy!(dst, default_rng())
 copy!(::_GLOBAL_RNG, src::MersenneTwister) = copy!(default_rng(), src)
 copy(::_GLOBAL_RNG) = copy(default_rng())

stdlib/Random/src/Random.jl

@@ -136,8 +136,11 @@ the amount of precomputation, if applicable.
 *types* and *values*, respectively. [`Random.SamplerSimple`](@ref) can be used to store
 pre-computed values without defining extra types for only this purpose.
 """
-Sampler(rng::AbstractRNG, x, r::Repetition=Val(Inf)) = Sampler(typeof(rng), x, r)
-Sampler(rng::AbstractRNG, ::Type{X}, r::Repetition=Val(Inf)) where {X} = Sampler(typeof(rng), X, r)
+Sampler(rng::AbstractRNG, x, r::Repetition=Val(Inf)) = Sampler(typeof_rng(rng), x, r)
+Sampler(rng::AbstractRNG, ::Type{X}, r::Repetition=Val(Inf)) where {X} =
+    Sampler(typeof_rng(rng), X, r)
+
+typeof_rng(rng::AbstractRNG) = typeof(rng)
 
 Sampler(::Type{<:AbstractRNG}, sp::Sampler, ::Repetition) =
     throw(ArgumentError("Sampler for this object is not defined"))

stdlib/Random/test/runtests.jl

@@ -770,4 +770,7 @@ end
         B = fill!(B, 1.0)
         @test rand!(GLOBAL_RNG, A, x) === A == rand!(mt, B, x) === B
     end
+    # issue #33170
+    @test Sampler(GLOBAL_RNG, 2:4, Val(1)) isa SamplerRangeFast
+    @test Sampler(GLOBAL_RNG, 2:4, Val(Inf)) isa SamplerRangeFast
 end