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Re: [aether-users] Sort dependencies topologically
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Thanks for your tips! I was able to achieve what I want by playing with the DependencyGraphTransformers.
Cheers,
Jérémy
On Tue, Nov 15, 2011 at 7:38 PM, Benjamin Bentmann
<bentmann@xxxxxxxxxxxx> wrote:
Jérémy wrote:
I'm trying to sort the dependencies [...] in a topological way. I tried to
use the PreorderNodeListGenerator from Aether.
Let's start with some minor recap of graph theory. Unless your input DAG posses additional properties, there can be several topological orderings [0], so seeing a different output sequence when you change dependency declaration order in the POM can be expected. A reverse postordering of a DAG delivers a topological sorting [1]. A reverse postordering is not the same as a preordering. That said, it's not clear to me why you picked the PreorderNodeListGenerator for the task.
I have the feeling that PreorderNodeListGenerator sorts a reduced graph,
where the conflicts and so have already been resolved.
The PreorderNodeListGenerator like any other DependencyVisitor visits the graph that has been provided to it by the caller. In your case, this is the output of collectDependencies(). Using the default settings provided by Maven this produces a dependency tree (!) where conflicts have been resolved. Such a tree does no longer encode all dependency relationships and cannot be used as input for a topological sort.
To create the graph you need, you need to employ a custom DependencyGraphTransformer [2] (via a new DefaultRepositorySystemSession). See NearestVersionConflictResolver as an example which is the one resolving version conflicts and pruning the conflicting nodes from the graph.
Benjamin
[0] http://en.wikipedia.org/wiki/Topological_sorting#Uniqueness
[1] http://en.wikipedia.org/wiki/Depth-first_search#Output_of_a_depth-first_search
[2] https://docs.sonatype.org/display/AETHER/Introduction
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