dot crashes with assertion failed on graph with some combinations of duplicated edges

[Stéphane Gourichon]

When processing some source files with a number of duplicated edges (that is, there exist some nodes A and B such that several edges A->B are declared with various properties), dot fails to produce an output. Usual source files are processed correctly.

Bug exists upstream with detailed steps to reproduce on http://www.graphviz.org/mantisbt/view.php?id=2456 but I could not create an account there (or even login anonymously). This bug report on LaunchPad may be useful to confirm it affects multiple users.

I suspect the reason is duplicated edges because the only Google answer on the assertion failure message is on that Mantis page, and the graphs I was working on do have a number of duplicated edges.

1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu

LC_ALL=C lsb_release -rd

Description: Ubuntu 14.04.2 LTS
Release: 14.04

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center

apt-cache policy graphviz

graphviz:
  Installé : 2.36.0-0ubuntu3.1
  Candidat : 2.36.0-0ubuntu3.1
 Table de version :
 *** 2.36.0-0ubuntu3.1 0
        500 http://fr.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.36.0-0ubuntu3 0
        500 http://fr.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

3) What you expected to happen

A graphic file is generated.

4) What happened instead

Graphviz stops with message:

dot: class2.c:149: merge_chain: Assertion `(((Agedgeinfo_t*)(((Agobj_t*)(e))->data))->to_virt) == ((void *)0)' failed.

# Additional information

Also observed with graphviz-2.38 on Ubuntu 14.10.

Bug exists upstream with detailed steps to reproduce on http://www.graphviz.org/mantisbt/view.php?id=2456 but I could not create an account there (or even login anonymously). This bug report on LaunchPad may be useful to confirm it affects multiple users.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: graphviz 2.36.0-0ubuntu3.1
ProcVersionSignature: Ubuntu 3.13.0-35.62-generic 3.13.11.6
Uname: Linux 3.13.0-35-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.7
Architecture: amd64
Date: Wed Mar 18 12:01:27 2015
InstallationDate: Installed on 2014-05-15 (306 days ago)
InstallationMedia: Xubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: graphviz
UpgradeStatus: No upgrade log present (probably fresh install)

[Stéphane Gourichon (stephane-gourichon-lpad)]

Bug report for Ubuntu 14.04 is on #1433541
Bug report for Ubuntu 14.10 is on #1433540

[Stéphane Gourichon (stephane-gourichon-lpad)]

Bug report for Ubuntu 14.04 is on https://bugs.launchpad.net/ubuntu/+source/graphviz/+bug/1433541
Bug report for Ubuntu 14.10 is on https://bugs.launchpad.net/ubuntu/+source/graphviz/+bug/1433540

[Stéphane Gourichon (stephane-gourichon-lpad)]

Removing a "rank=same" constraint in the graph fixed the problem in practice for me, and also in the upstream steps to reproduce.
I encourage anyone stumbling on the same bug to at least add a comment here so that upstream author get to know that the bug affects users in real-world use and so needs to be fixed.