Make PassthroughRNG dispatch survive overlay method-table shadowing

Project.toml

@@ -1,6 +1,6 @@
 name = "PoissonRandom"
 uuid = "e409e4f3-bfea-5376-8464-e040bb5c01ab"
-version = "0.4.7"
+version = "0.4.8"
 
 [deps]
 LogExpFunctions = "2ab3a3ac-af41-5b50-aa03-7779005ae688"

src/PoissonRandom.jl

@@ -13,6 +13,15 @@ Random.rand(rng::PassthroughRNG) = rand()
 Random.randexp(rng::PassthroughRNG) = randexp()
 Random.randn(rng::PassthroughRNG) = randn()
 
+# When an overlay method table (e.g. CUDA.jl's `@device_override
+# Random.randexp(::AbstractRNG)`) shadows the methods above, the overlay body
+# runs with rng::PassthroughRNG and may call `Random.rand(rng, UInt52Raw())`
+# or `Random.rand(rng, T)`. The stdlib Sampler chain bottoms out at
+# `_rand52(r, rng_native_52(r))` → `rand(r, UInt64)`; provide those so the
+# chain still reaches bare rand(T) and the device-side default_rng path.
+Random.rng_native_52(::PassthroughRNG) = UInt64
+Random.rand(rng::PassthroughRNG, ::Type{T}) where {T} = rand(T)
+
 count_rand(λ::Real) = count_rand(Random.default_rng(), λ)
 function count_rand(rng::AbstractRNG, λ::Real)
     n = 0

test/runtests.jl

@@ -116,6 +116,22 @@ end
     end
 end
 
+@testset "PassthroughRNG dispatch" begin
+    using Random: Random, UInt52Raw
+    prng = PassthroughRNG()
+    # The CUDA.jl @device_override Random.randexp(::AbstractRNG) shadows our
+    # specific Random.randexp(::PassthroughRNG) on the GPU because Julia's
+    # OverlayMethodTable returns overlay matches without consulting the base
+    # table when the overlay fully covers the signature. The override body
+    # then calls these against PassthroughRNG; if they MethodError, kernel
+    # compilation fails with InvalidIRError on jl_f_throw_methoderror.
+    @test Random.rng_native_52(prng) === UInt64
+    @test Random.rand(prng, UInt52Raw()) isa UInt64
+    @test Random.rand(prng, UInt64) isa UInt64
+    @test Random.rand(prng, Float32) isa Float32
+    @test Random.rand(prng, Float64) isa Float64
+end
+
 if get(ENV, "GROUP", "all") == "all" || get(ENV, "GROUP", "all") == "nopre"
     @testset "Allocation Tests" begin
         include("alloc_tests.jl")