Can't deserialize something from an anonymous module

[quinnj]

It seems like this should be able to work?

julia> using Serialization

julia> module Foo; foo() = "hey"; end
Main.Foo

julia> io = IOBuffer()
IOBuffer(data=UInt8[...], readable=true, writable=true, seekable=true, append=false, size=0, maxsize=Inf, ptr=1, mark=-1)

julia> serialize(io, Foo.foo)

julia> seekstart(io)
IOBuffer(data=UInt8[...], readable=true, writable=true, seekable=true, append=false, size=30, maxsize=Inf, ptr=1, mark=-1)

julia> deserialize(io)
foo (generic function with 1 method)

julia> m = Module()
Main.anonymous

julia> Core.eval(m, :(foo() = "hey"))
foo (generic function with 1 method)

julia> io = IOBuffer()
IOBuffer(data=UInt8[...], readable=true, writable=true, seekable=true, append=false, size=0, maxsize=Inf, ptr=1, mark=-1)

julia> serialize(io, m.foo)

julia> seekstart(io)
IOBuffer(data=UInt8[...], readable=true, writable=true, seekable=true, append=false, size=36, maxsize=Inf, ptr=1, mark=-1)

julia> deserialize(io)
ERROR: UndefVarError: `anonymous` not defined
Stacktrace:
  [1] deserialize_module(s::Serializer{IOBuffer})
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:996
  [2] handle_deserialize(s::Serializer{IOBuffer}, b::Int32)
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:895
  [3] deserialize(s::Serializer{IOBuffer})
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:813
  [4] deserialize_datatype(s::Serializer{IOBuffer}, full::Bool)
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:1389
  [5] handle_deserialize(s::Serializer{IOBuffer}, b::Int32)
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:866
  [6] deserialize(s::Serializer{IOBuffer})
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:813
  [7] handle_deserialize(s::Serializer{IOBuffer}, b::Int32)
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:873
  [8] deserialize(s::Serializer{IOBuffer})
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:813
  [9] handle_deserialize(s::Serializer{IOBuffer}, b::Int32)
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:919
 [10] deserialize
    @ ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:813 [inlined]
 [11] deserialize(s::IOBuffer)
    @ Serialization ~/juliax/usr/share/julia/stdlib/v1.10/Serialization/src/Serialization.jl:800
 [12] top-level scope
    @ REPL[12]:1

[quinnj]

Or perhaps this is expected since Main.anonymous isn't really referring to a specific module, and how can serialize know which anonymous module you're referring to exactly?

[Seelengrab]

If you do julia> const anonymous = 1, you also hit a type assert (rightly so):

julia> deserialize(io)
ERROR: TypeError: in typeassert, expected Module, got a value of type Int64
Stacktrace:

So either serialize needs to preserve the information that the parent module was anonymous and recreate it somehow, or serialization of functions in an anonymous module drops that information (or we disallow it entirely, seeing as we can't correctly deserialize this now, I don't think anyone is relying on this working right now without a bug coming for them later on).

[JeffBezanson]

If we can detect an anonymous module (which we probably can by seeing that its binding doesn't exist or doesn't point to it), we could handle its functions like anonymous functions in Main, i.e. serialize them by contents instead of name. Would that be useful in this situation?

[quinnj]

Ah yeah, that would be helpful.

[ablaom]

Yeah, I think this would also resolve the Documenter.jl error cross-referenced above, thanks.