multi-edges generate error on non-strict digraph

[LeoAlex0]

Version

github.com/goccy/go-graphviz v0.0.9

Example Code

package main

import (
	"os"

	"github.com/goccy/go-graphviz"
)

func main() {
	graph := graphviz.New()
	g, _ := graph.Graph(graphviz.Directed, graphviz.Name("G"))

	n1, _ := g.CreateNode("1")
	n2, _ := g.CreateNode("2")
	g.CreateEdge("e1", n1, n2)
	g.CreateEdge("re1", n2, n1)

	g.CreateEdge("e2", n1, n2)
	g.CreateEdge("re2", n2, n1)

	graph.Render(g, graphviz.Format(graphviz.DOT), os.Stdout)
}

Real Output

digraph G {
	graph [bb="0,0,54,108"];
	node [label="\N"];
	1	 [height=0.5,
		pos="27,90",
		width=0.75];
	2	 [height=0.5,
		pos="27,18",
		width=0.75];
	1 -> 2 [key=e1,
	pos="e,21.105,35.593 21.084,72.202 20.28,64.181 20.057,54.523 20.416,45.596"];
2 -> 1 [key=re1,
pos="e,32.916,72.202 32.895,35.593 33.709,43.586 33.942,53.236 33.593,62.176"];
}

Expect

As the graphviz doc, a non-strict graph should allow multi-edges without merging them.

so it should output something like:

digraph G {
	graph [bb="0,0,54,108"];
	node [label="\N"];
	1	 [height=0.5,
		pos="27,90",
		width=0.75];
	2	 [height=0.5,
		pos="27,18",
		width=0.75];
	1 -> 2 [key=e1,
	pos="e,21.105,35.593 21.084,72.202 20.28,64.181 20.057,54.523 20.416,45.596"];
  1 -> 2 [key=e2,
	pos="e,21.105,35.593 21.084,72.202 20.28,64.181 20.057,54.523 20.416,45.596"];
2 -> 1 [key=re1,
pos="e,32.916,72.202 32.895,35.593 33.709,43.586 33.942,53.236 33.593,62.176"];
2 -> 1 [key=re2,
pos="e,32.916,72.202 32.895,35.593 33.709,43.586 33.942,53.236 33.593,62.176"];
}

[nevivurn]

I was facing a similar issue, I believe this is a bug in upstream graphviz that has been fixed right after 2.40.1 (in dbe61e9fe), which is what this library uses.

I'm not too familiar with writing cgo wrappers, how hard would it be to update this library to use a more recent graphviz release? Also see #42.

[triztian]

@goccy This is a wonderful package, thank you!

I've also encountered this issue and would like to take a jab at updating the GraphViz version. In #42 you'd mentioned providing a make update/graphviz/<VERSION> command. Is there any documentation of how to do it? I don't see a Makefile in the master branch, alternatively if you have any general instructions or pointers of how to the the migration manually I'd be happy to go over them.

Many thanks in advance!

[mcrakhman]

Hi @goccy! The library is great, but multi-edges fix would be greatly appreciated :-) Any news on updating graphviz or making Makefile available?

Thanks!

[ankon]

I'd also love to have multi-edges work, but it seems updating the cgraph library here might be a major project (probably first sync with 2.50.1, and then go to 3.0.0?)

But, for the fun of it I tried to simply apply the referenced change directly, and that works just fine.

git clone https://github.com/goccy/go-graphviz
cd go-graphviz
wget -qO - https://gitlab.com/graphviz/graphviz/-/commit/dbe61e9fe.diff | patch internal/ccall/cgraph/edge.c

And in your own project modify go.mod to use a replace.

@goccy would you accept a PR applying this change?