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https://issues.apache.org/jira/browse/MRESOLVER-62?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17520113#comment-17520113
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wei cai commented on MRESOLVER-62:
----------------------------------
This issue should be resolved by the Skipper. Like below, the ^x dependent by
y:1 would be simply skipped as x:1 is already resolved before with a shallower
depth.
{noformat}
+- gid:a:1
| \- gid:x:1 (x)
| \- gid:y:1
| \- ^x{noformat}
However the tests did not pass though (applied the patch). This is because:
* In my ticket, we use skipper to resolve the least tree (with conflicts
skipped) and then delegate to ConflictResolver to resolve conflicts. This means
Skipper handles most of the conflicts (except the scope conflicts among
duplicate nodes) in advance for ConflictResolver.
* For this ticket, it is expecting a fix in ConflictResolver. And the tests
provided in this ticket is testing NearestVersionSelector which is part of
ConflictResolver.
[~michael-o]
This might be still an issue in ConflictResolver, If skipper is proved to be
helpful for the issue in this post, then we can say skipper may workaround such
issues however the fault/bug might be still there in ConflictResolver.
May I know your concern? If you need my help to prove Skipper can fix issue in
this post, then I can modify the tests patch provided in this post.
> 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: Critical
> Labels: intern
> 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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