MetaGraph to DOT seems buggy

[tecosaur]

MWE

julia> using MetaGraphsNext # v0.6.0

julia> struct Foo end

julia> g2 = MetaGraph(DiGraph(), label_type=Int, vertex_data_type=Foo)
Meta graph based on a SimpleDiGraph{Int64} with vertex labels of type Int64, vertex metadata of type Foo, edge metadata of type Nothing, graph metadata given by nothing, and default weight 1.0

julia> savegraph("data.dot", g2, DOTFormat())
ERROR: MethodError: no method matching length(::Foo)

Closest candidates are:
  length(::LibGit2.GitStatus)
   @ LibGit2 ~/.julia/juliaup/julia-1.10.0-rc1+0.x64.linux.gnu/share/julia/stdlib/v1.10/LibGit2/src/status.jl:21
  length(::Tables.DictRowTable)
   @ Tables ~/.julia/packages/Tables/NSGZI/src/dicts.jl:118
  length(::Base.MethodSpecializations)
   @ Base reflection.jl:1164
  ...

Stacktrace:
 [1] show_meta_list(io::IOStream, meta::Foo)
   @ MetaGraphsNext ~/.julia/packages/MetaGraphsNext/YvA1m/src/persistence.jl:31
 [2] savedot(io::IOStream, meta_graph::MetaGraph{…})
   @ MetaGraphsNext ~/.julia/packages/MetaGraphsNext/YvA1m/src/persistence.jl:76
 [3] #32
   @ ~/.julia/packages/MetaGraphsNext/YvA1m/src/persistence.jl:100 [inlined]
 [4] open(::MetaGraphsNext.var"#32#33"{MetaGraph{…}}, ::String, ::Vararg{String}; kwargs::@Kwargs{})
   @ Base ./io.jl:396
 [5] open
   @ Base ./io.jl:393 [inlined]
 [6] savegraph(file::String, meta_graph::MetaGraph{…}, ::DOTFormat)
   @ MetaGraphsNext ~/.julia/packages/MetaGraphsNext/YvA1m/src/persistence.jl:99
 [7] top-level scope
   @ REPL[13]:1
Some type information was truncated. Use `show(err)` to see complete types.

[gdalle]

It's not clear to me how custom Julia types should be serialized as part of the DOT format.

https://en.m.wikipedia.org/wiki/DOT_(graph_description_language)

Perhaps JLD and friends are better options for this use case?

[tecosaur]

In this case, I'm just serialising to DOT to try it as an alternative for plotting. Perhaps a better behaviour than current would be either:

• Ignoring the vertex data
• Using a custom vertex data serialisor keyword argument

[gdalle]

That sounds reasonable, if you want to open a PR because it serves your use case I'll be happy to try and review