[jira] [Created] (FELIX-5601) issues resolving with substitutable exports when the export is the last available provider

["Thomas Watson (JIRA)" <ji...@apache.org>]

Thomas Watson created FELIX-5601:
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             Summary: issues resolving with substitutable exports when the export is the last available provider
                 Key: FELIX-5601
                 URL: https://issues.apache.org/jira/browse/FELIX-5601
             Project: Felix
          Issue Type: Bug
          Components: Resolver
            Reporter: Thomas Watson
            Assignee: Thomas Watson


Substitutable exports that are used by other exported packages can cause a case where a valid solution cannot be found when one exists.  The issue only can occur when a substitutable export is the only valid candidate left for a resources mandatory requirement and the resolver decides to permute the substitutable requirement becaused of a used blame.  Something like the following resources

resource A1
  provides pkg X v1
  provides pkg Y v1 uses->X
  provides pkg Z v1 uses->Y

resource A2
  provides pkg X v2
  provides pkg Y v2 uses->X
  provides pkg Z v2 uses->Y
  import pkg X v[2,4)
  import pkg Y v[2,4)
  import pkg Z v[2,4)

resource A3
  provides pkg X v3
  provides pkg Y v3 uses->X
  provides pkg Z v3 uses->Y
  import pkg X v[2,4)
  import pkg Y v[2,4)
  import pkg Z v[2,4)

resource B1
  provides pkg W v1 uses->Z
  import pkg Z v[1,4)

resource C1
  imports pkg X v[3,4)

Resolve all resources A1, A2, A3, B1, C1 as mandatory resources.  This will result in resolution error for B1 because it is exposed to two versions of X through two uses blame chains.  The reason this fails is because the resolver first chooses to permute the substitutable requirement from A3 for X which causes X v3 to no longer be available for C1 to import.  This causes an error and the permutation fails and all other permutations based off that permutation will be ignored.  If instead the resolver would not permute the requirement for X from A3 the resolver would find a valid solution.



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