Fix could not import Graphs.prufer_decode warning

[simonschoelly]

There was an incorrect import statement for prufer_code in the SimpleGraphs submodule. This PR removes it.

[simonschoelly]

@SimonCoste would you mind doing a quick review?

[codecov]

Codecov Report

Merging #215 (228262d) into master (c4360cf) will not change coverage.
The diff coverage is n/a.

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[SimonCoste]

How did you get this warning ?
Indeed I don't understand why the import statement is not correct. Shouldn't I import prufer_decode since I use it in the generator uniform_tree ?

[simonschoelly]

Usually one does not notice, but when Graphs.jl gets precompiled there is a warning:

julia> using Graphs
[ Info: Precompiling Graphs [86223c79-3864-5bf0-83f7-82e725a168b6]
WARNING: could not import Graphs.prufer_decode into SimpleGraphs

I did't realize it, when I made this PR, but I think the reason is, that in src/Graphs.jl we first include src/SimpleGraphs/SimpleGraphs.jl and only afterwards src/trees/prufer.jl - so then the prufer_decode symbol simply does not exist.
But including src/trees/prufer.jl before would also not help, because that file relies on the definition of SimpleGraph.

I can't think of any pretty solution to that - but maybe we should simply move all the code into the SimpleGraphs submodule? Another solution would probably be, to declare an function without methods with

    function prufer_decode end

right before including src/SimpleGraphs/SimpleGraphs.jl - this is also not very nice though, because then we would keep the cyclic dependency.

[SimonCoste]

I feel like including prufer_decode and other tree-related functions inside SimpleGraphs is really odd, since there are almost no other functions/algorithms implemented in SimpleGraphs.

What about modifying trees/prufer.jl so that it does not rely on SimpleGraphs ? It only uses the SimpleGraph{T} type in two places :

• as a return type annotation for prufer_decode in

  Graphs.jl/src/trees/prufer.jl

  Line 40 in c4360cf

  function prufer_decode(code::AbstractVector{T})::SimpleGraph{T} where {T<:Integer}

• as a type annotation in prufer_encode in

  Graphs.jl/src/trees/prufer.jl

  Line 74 in c4360cf

  function prufer_encode(G::SimpleGraph{T})::Vector{T} where {T<:Integer}

Maybe the simplest thing is to get rid of those in a consistent manner, by replacing them with Graph .