access to undefined reference

[mhauru]

julia> module MWE

       using Libtask

       obs = Any[:a,:b]

       produce_wrapper(x) = Libtask.produce(x)
       Libtask.might_produce(::Type{<:Tuple{typeof(produce_wrapper),Any}}) = true

       function f(obs)
           for o in obs
               produce_wrapper(o)
           end
           return nothing
       end

       tt = Libtask.TapedTask(nothing, f, obs)
       for i in 1:length(obs)
           println(Libtask.consume(tt))
       end

       end
a
ERROR: UndefRefError: access to undefined reference
Stacktrace:
  [1] getproperty
    @ ./Base.jl:49 [inlined]
  [2] getindex
    @ ./refvalue.jl:59 [inlined]
  [3] get_ref_at
    @ ~/.julia/packages/Libtask/7zdQp/src/copyable_task.jl:1074 [inlined]
  [4] produce_wrapper
    @ ./REPL[2]:7 [inlined]
  [5] (::Tuple{Base.RefValue{Symbol}, Base.RefValue{Int32}})(none::typeof(Main.MWE.produce_wrapper), none::Symbol)
    @ Base.Experimental ./<missing>:0
  [6] (::MistyClosures.MistyClosure{Core.OpaqueClosure{Tuple{typeof(Main.MWE.produce_wrapper), Symbol}, Union{Symbol, Libtask.ProducedValue{Symbol}}}})(::Function, ::Symbol)
    @ MistyClosures ~/.julia/packages/MistyClosures/4rFSA/src/MistyClosures.jl:22
  [7] (::Libtask.DynamicCallable{Dict{Any, Any}})(::Function, ::Symbol)
    @ Libtask ~/.julia/packages/Libtask/7zdQp/src/copyable_task.jl:1153
  [8] f
    @ ./REPL[2]:11 [inlined]
  [9] (::Tuple{…})(none::typeof(Main.MWE.f), none::Vector{…})
    @ Base.Experimental ./<missing>:0
 [10] consume(t::Libtask.TapedTask{Nothing, Tuple{typeof(Main.MWE.f), Vector{Any}}, MistyClosures.MistyClosure{Core.OpaqueClosure{Tuple{typeof(Main.MWE.f), Vector{Any}}, Union{Nothing, Libtask.ProducedValue}}}})
    @ Libtask ~/.julia/packages/Libtask/7zdQp/src/copyable_task.jl:347
 [11] top-level scope
    @ ./REPL[2]:19
Some type information was truncated. Use `show(err)` to see complete types.

That obs = Any[:a,:b] has eltype Any seems to be significant, as is the fact that at least some of the values are symbols or strings. This works as expected for e.g. obs = [:a,:b,:c,:d] and obs = Any[1,2,true,0.3].

Any hints as to what this could possibly be about are very welcome. I'll have a look, but I don't have an idea for where to start currently.

[yebai]

I looked at the code but didn't see anything obvious that could lead to this bug.

[mhauru]

I think the problem might be that functions that do return Libtask.produce(...) don't get the ref for the return value set, and then when we continue execution after a produce statement and try to return, the modified IR tries to access a ref that is undefined.

[mhauru]

#191 fixes the crash, but the same MWE now fails in a different way. Namely, it only produces :a:

julia> module MWE

       using Libtask

       obs = Any[:a,:b]

       produce_wrapper(x) = Libtask.produce(x)
       Libtask.might_produce(::Type{<:Tuple{typeof(produce_wrapper),Any}}) = true

       function f(obs)
           for o in obs
               produce_wrapper(o)
           end
           return nothing
       end

       tt = Libtask.TapedTask(nothing, f, obs)
       for i in 1:length(obs)
           println(Libtask.consume(tt))
       end

       end
a
nothing

This is the behaviour I originally saw in TuringLang/Turing.jl#2585, and that this MWE was trying to minimise in the first place.

[yebai]

Fixed by #191 and #192