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https://issues.apache.org/jira/browse/MRESOLVER-62?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sylwester Lachiewicz reassigned MRESOLVER-62:
---------------------------------------------
Assignee: (was: Sylwester Lachiewicz)
> Resolver can skip cyclic dependencies underneath removed nodes
> --------------------------------------------------------------
>
> Key: MRESOLVER-62
> URL: https://issues.apache.org/jira/browse/MRESOLVER-62
> Project: Maven Resolver
> Issue Type: Bug
> Components: resolver
> Affects Versions: Maven Artifact Resolver 1.1.1
> Reporter: Toby Hammett
> Priority: Minor
> Attachments: maven-resolver-cycle-underneath-removed-node.patch
>
>
> While updating dependencies in one of my company's Maven projects, I got a
> StackOverflowError involving infinite recursion at
> {{org.apache.maven.RepositoryUtils#toArtifacts}}. After some investigation, I
> believe I have traced the issue to a bug in ConflictResolver which can occur
> when encountering multiple dependency cycles. Specifically, I think the
> criteria for failure are:
> * One cycle appears nearer to the root than the other cycle as a child of a
> node that will be removed.
> * That cycle is also a child of the other cycle elsewhere in the dependency
> graph.
> For example, here is a dependency graph analogous to the one I was working
> with when I encountered the StackOverflowError:
> {noformat}
> (null)
> +- gid:a:1
> | \- gid:x:1 (x)
> | \- gid:y:1
> | \- ^x
> +- gid:a:2
> +- gid:b:1
> | +- gid:c:1
> | \- gid:d:1 (d)
> | \- ^x
> \- gid:m:1
> \- gid:n:1
> +- gid:p:1
> | \- gid:q:1
> \- gid:q:2
> \- gid:p:2
> \- ^d
> {noformat}
> This graph has a cycle ({{x}} and {{y}}) underneath a node that is removed
> from the tree ({{a:1}}). This cycle also appears as a child of another cycle.
> Specifically, {{q}} and {{p}} depends on {{d}}, which depends on {{x}}.
> After conflicts are resolved in this graph, the node for {{gid:y:1}} still
> has a reference to {{gid:x:1}}, although I believe it should have been
> removed. This cycle in the graph led to the StackOverflowError I observed.
> Another example, derived from the first, shows a slightly different problem:
> {noformat}
> (null)
> +- gid:a:1
> | \- gid:x:1 (x)
> | \- gid:y:1
> | \- ^x
> +- gid:a:2
> \- gid:m:1
> \- gid:n:1
> +- gid:p:1
> | \- gid:q:1
> \- gid:q:2
> |- gid:p:2
> \- ^x
> {noformat}
> In this case, as with the first, there is a cycle underneath a node that will
> be removed. That cycle ({{x}} and {{y}}) is also a dependency of node
> {{gid:q:2}}, which is itself a member of a cycle with {{p}}. When conflicts
> are resolved in this case, the resulting graph does not contain {{gid:x:1}}
> at all!
>
> A potential workaround for this issue is to declare a direct dependency on
> one of the artifacts in the cycle that is not handled correctly.
>
> I have attached a patch for maven-resolver-util which adds both of the
> preceding examples as unit tests. Please let me know if there's any other
> information I can provide.
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