Throw an error if trying to access unassigned data in Base.RefValue (#…

…45829)

Co-authored-by: Kristoffer Carlsson <kcarlsson89@gmail.com>

base/refvalue.jl

@@ -45,7 +45,10 @@ function unsafe_convert(P::Union{Type{Ptr{T}},Type{Ptr{Cvoid}}}, b::RefValue{T})
         # If it is actually an immutable, then we can't take it's pointer directly
         # Instead, explicitly load the pointer from the `RefValue`,
         # which also ensures this returns same pointer as the one rooted in the `RefValue` object.
-        p = pointerref(Ptr{Ptr{Cvoid}}(pointer_from_objref(b)), 1, Core.sizeof(Ptr{Cvoid}))
+        p = atomic_pointerref(Ptr{Ptr{Cvoid}}(pointer_from_objref(b)), :monotonic)
+    end
+    if p == C_NULL
+        throw(UndefRefError())
     end
     return p
 end

test/core.jl

@@ -7847,6 +7847,17 @@ import .Foo45350: x45350
 f45350() = (global x45350 = 2)
 @test_throws ErrorException f45350()
 
+@testset "Error behavior of unsafe_convert for RefValue" begin
+    b = Base.RefValue{Int}()
+    @test Base.unsafe_convert(Ptr{Int}, b) !== C_NULL
+    b = Base.RefValue{Base.RefValue{Int}}()
+    # throws because we hit `b.x`
+    @test_throws Core.UndefRefError Base.unsafe_convert(Ptr{Base.RefValue{Int}}, b)
+    # throws because we hit `b.x`
+    b = Base.RefValue{Integer}()
+    @test_throws Core.UndefRefError Base.unsafe_convert(Ptr{Integer}, b)
+end
+
 # #46503 - redefine `invoke`d methods
 foo46503(@nospecialize(a), b::Union{Vector{Any}, Float64, Nothing}) = rand()
 foo46503(a::Int, b::Nothing) = @invoke foo46503(a::Any, b)